Almabrok, MH, McLaughlan, R, Vessalas, K & Thomas, P 2019, 'Effect of oil contaminated aggregates on cement hydration', American Journal of Engineering Research (AJER), vol. 8, no. 5, pp. 81-89.
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Canola oil, refined mineral oil, and crude oil additions up to 10% of the aggregate mass inPortland cement mortars were found to decrease the 28-day compressive strength by 71%, 75% and 50%,respectively, and retard setting times. There was a progressive impact upon cement hydration as the oil contentincreased in mortars. Only in the case of vegetable oil and refined mineral oil could strength loss be attributedin part to cement hydration inhibition, as evidenced by reduced total evolved heat. It is likely thatmicrostructural effects were also a key factor in strength loss for all mortars particularly for those containingcrude oil.
Aslani, F, Hou, L, Nejadi, S, Sun, J & Abbasi, S 2019, 'Experimental analysis of fiber‐reinforced recycled aggregate self‐compacting concrete using waste recycled concrete aggregates, polypropylene, and steel fibers', Structural Concrete, vol. 20, no. 5, pp. 1670-1683.
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AbstractSelf‐compacting concrete (SCC) is a cementitious composite which serves complex formworks without mechanical vibrations with superior deformability and high resistance to segregation. Besides, the recycled aggregate concrete (RAC) is also developing rapidly and along with the ever‐increasing sustainable demand for infrastructure. The combination of the fibers, RAC, and SCC may create advantages for the construction industry. In this study, the polypropylene (PP) fiber at 0.1, 0.15, 0.2, and 0.25% volume fractions and steel fibers at 0.25, 0.5, 0.75, and 1% volume fractions are introduced into fiber‐reinforced recycled aggregate self‐compacting concrete (FR‐RASCC). Both fresh property and hardened mechanical performance, comprising compressive and tensile strengths and modulus of elasticity are analyzed. The fibers validate the optimal 0.1% volume fraction for PP fiber and 0.75% volume fraction for steel fiber. In addition, the results are proved to enhance the mechanical properties and reduce cracking despite the negative impact on the fresh property. Moreover, the experimental outcomes are compared with previous researches to establish the linear model, demonstrating the relationship between fiber fraction and the mechanical properties.
Aung, Y, Khabbaz, H & Fatahi, B 2019, 'Mixed hardening hyper-viscoplasticity model for soils incorporating non-linear creep rate – H-creep model', International Journal of Plasticity, vol. 120, pp. 88-114.
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© 2019 Elsevier Ltd. This paper focuses on the deformation of soils considering the time-dependent stress-strain evolution. In this paper, a new mixed hardening hyper-viscoplasticity model is proposed for the derivation of the time-dependent constitutive behaviour of soils, with the intention to capture the variation in the shapes of the yield loci by pursuing non-associated flow rules and accounting for kinematic hardening effects. The distinctive departure from the existing viscoplasticity models is the application of thermodynamics, based upon the use of internal variables, to postulate free-energy and dissipation potential functions, from which the corresponding yield locus, isotropic and kinematic hardening laws, flow rules and the elasticity law are deduced in a systematic procedure. The kinematic hardening behaviour of the yield locus is considered using the shift stress, resulting from the additional plastic component of the free-energy function. A non-linear creep formulation is postulated to address the limitation of over-estimating long-term settlement and incorporated into the model for more reliable predictions. The major parameters required for the model are identified, along with the summary of descriptions on how the model parameters can readily be determined. Non-associated behaviour is found to be a natural consequence of this approach, whenever the division between dissipated and stored plastic work is not equal. This study aims to provide a theoretical background and a numerical implementation for those who are interested in the advancement of constitutive modelling of soil behaviour under the framework of hyperplasticity. Validity and versatility of the proposed constitutive model are evaluated against triaxial and oedometer test results available in literature.
Chen, W, Zhang, Y, Wang, D & Wu, C 2019, 'Investigation on damage development of AP1000 nuclear power plant in strong ground motions with numerical simulation', Nuclear Engineering and Technology, vol. 51, no. 6, pp. 1669-1680.
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© 2019 Seismic safety is considered to be one of the key design objectives of AP1000 nuclear power plant (NPP) in strong earthquakes. Dynamic behavior, damage development and aggravation effect are studied in this study for the three main components of AP1000 NPP, namely reinforced concrete shield building (RCSB), steel vessel containment (SVC) and reinforced concrete auxiliary building (RCAB). Characteristics including nonlinear concrete tension and compressive constitutions with plastic damage are employed to establish the numerical model, which is further validated by existing studies. The author investigates three earthquakes and eight input levels with the maximum magnitude of 2.4 g and the results show that the concrete material of both RCSB and RCAB have suffered serious damage in intense earthquakes. Considering RCAB in the whole NPP, significant damage aggravation effect can be detected, which is mainly concentrated at the upper intersection between RCSB and RCAB. SVC and reinforcing bar demonstrate excellent seismic performance with no obvious damage.
Dackermann, U, Smith, WA, Alamdari, MM, Li, J & Randall, RB 2019, 'Cepstrum-based damage identification in structures with progressive damage', Structural Health Monitoring, vol. 18, no. 1, pp. 87-102.
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This article aims at developing a new framework to identify and assess progressive structural damage. The method relies solely on output measurements to establish the frequency response functions of a structure using cepstrum-based operational modal analysis. Two different damage indicative features are constructed using the established frequency response functions. The first damage feature takes the residual frequency response function, defined as the difference in frequency response function between evolving states of the structure, and then reduces its dimension using principle component analysis; while in the second damage indicator, a new feature based on the area under the residual frequency response function curve is proposed. The rationale behind this feature lies in the fact that damage often affects a number of modes of the system, that is, it affects the frequency response function over a wide range of frequencies; as a result, this quantity has higher sensitivity to any structural change by combining all contributions from different frequencies. The obtained feature vectors serve as inputs to a novel multi-stage neural network ensemble designed to assess the severity of damage in the structure. The proposed method is validated using extensive experimental data from a laboratory four-girder timber bridge structure subjected to gradually progressing damage at various locations with different severities. In total, 13 different states of the structure are considered, and it is demonstrated that the new damage feature outperforms the conventional principle component analysis–based feature. The contribution of the work is threefold: first, the application of cepstrum-based operational modal analysis in structural health monitoring is further validated, which has potential for real-life applications where only limited knowledge of the input is available; second, a new damage feature is proposed and its superior performance is demonstrated;...
Dadzie, J, Runeson, G & Ding, G 2019, 'Assessing determinants of sustainable upgrade of existing buildings', Journal of Engineering, Design and Technology, vol. 18, no. 1, pp. 270-292.
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PurposeEstimates show that close to 90% of the buildings we will need in 2050 are already built and occupied. The increase in the existing building stock has affected energy consumption thereby negatively impacting the environment. The purpose of this paper is to assess determinants of sustainable upgrade of existing buildings through the adoption and application of sustainable technologies. The study also ranks sustainable technologies adopted by the professionals who participated in the survey with an in-built case study.Design/methodology/approachAs part of the overall methodology, a detailed literature review on the nature and characteristics of sustainable upgrade and the sustainable technologies adopted was undertaken. A survey questionnaire with an in-built case study was designed to examine all the sustainable technologies adopted to improve energy consumption in Australia. The survey was administered to sustainability consultants, architects, quantity surveyors, facility managers and engineers in Australia.FindingsThe results show a total of 24 technologies which are mostly adopted to improve energy consumption in existing buildings. A factor analysis shows the main components as: lighting and automation, heating, ventilation and air conditioning (HAVC) systems and equipment, envelope, renewable energy and passive technologies.Originality/valueThe findings bridge the gap in the literature on the adoption and application of sustainable technologies to upgrade existing buildings. The technologies can be adopted to reduce the excessive energy consumption patterns in ex...
Dash, SK, Saikia, R & Nimbalkar, S 2019, 'Contact Pressure Distribution on Subgrade Soil Underlying Geocell Reinforced Foundation Beds', Frontiers in Built Environment, vol. 5.
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© Copyright © 2019 Dash, Saikia and Nimbalkar. High contact stresses generated in the foundation soil, owing to increased load, causes distress, instability, and large settlements. Present days, geocell reinforcement is being widely used for the performance improvement of foundation beds. Pressure distribution on subgrade soil in geocell reinforced foundation beds is studied through model tests and numerical analysis. The test data indicates that with provision of geocell reinforcement the contact pressure on the subgrade soil reduces significantly. Consequently, the subgrade soil tends to remain intact until large loadings on the foundation leading to significant performance improvement. Through numerical analysis it is observed that the geocells in the region under the footing were subjected to compression and beyond were in tension. This indicates that the geocell reinforcement right under the footing directly sustains the footing loading through mobilization of its compressive stiffness and bending rigidity. Whereas, the end portions of the geocell reinforcement, contribute to the performance improvement in a secondary manner through mobilization of anchorage derived from soil passive resistance and friction.
De Carvalho Gomes, S, Zhou, JL, Li, W & Long, G 2019, 'Progress in manufacture and properties of construction materials incorporating water treatment sludge: A review', Resources, Conservation and Recycling, vol. 145, pp. 148-159.
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© 2019 Elsevier B.V. Water treatment sludge (WTS) management is a growing global problem for water treatment plants (WTPs) and governments. Considering the scarcity of raw materials in many parts of the planet and unique properties of WTS, extensive research has been conducted on the application of WTS in the production of construction materials such as roof tiles, bricks, lightweight aggregates, cement, concrete and geopolymers. This paper critically reviews the progress in the application of WTS in construction materials, by synthesizing results from recent studies. Research findings have revealed that incorporation of ≤10% alum-based sludge in ceramic bricks is satisfactory with a small reduction of mechanical performance. Using the iron-based sludge, the bricks presented better mechanical strength than the reference clay-bricks. Concerning WTS application in concrete, 5% replacement of cement or sand by WTS was considered as the ideal value for the application in a variety of structural and non-structural concrete without adverse effect on concrete mechanical performance. Furthermore, this paper discusses sludge-amended concrete in terms of durability, potential leaching of toxic elements and cost, and suggests topics for future research on the sustainable management of WTS.
Ding, G & Ying, X 2019, 'Embodied and operating energy assessment of existing buildings – Demolish or rebuild', Energy, vol. 182, pp. 623-631.
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© 2019 Addressing climate change and energy efficiency of buildings challenge governments. Research studies to improve the efficiency of new buildings are many, but the potential of existing buildings to alleviate environmental problems is yet to be recognised. The economic development in China triggered the rapid growth of population and urbanisation. The government has experienced severe environmental problems due, among other things, to an increasing demand for housing. The demand for housing and environmental degradation have compelled the government to demolish historic houses for the construction of more efficient residential buildings. Nevertheless, the consumption of natural resources is essential considerations for redevelopment. The research has selected a south China town to conduct multiple case studies to analyse and compare the energy efficiency of historic and modern dwellings. The research reveals that modern building overall outperforms the historic houses in energy consumption for heating but consumes much higher energy for cooling over a 12-month period. However, the historic houses outperform the modern building in the embodied energy and carbon analysis. If these historic houses are to be replaced with energy efficient buildings, it will take approximately 18–41 years to recover the embodied energy invested in the materials for the new buildings.
Dong, W, Li, W, Lu, N, Qu, F, Vessalas, K & Sheng, D 2019, 'Piezoresistive behaviours of cement-based sensor with carbon black subjected to various temperature and water content', Composites Part B: Engineering, vol. 178, pp. 107488-107488.
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© 2019 Elsevier Ltd Cement-based sensor possesses unique properties for structural health monitoring (SHM) applications, such as low cost, high durability, adaptability and excellent sensitivity. The piezoresistivity of cement-based sensor possesses is often affected by working environments, which may limit its real potentials. In this study, the piezoresistive sensitivity and repeatability of cement-based sensors with carbon black (CB) under various environmental conditions were investigated. Under various temperatures ranging from −20 °C to 100 °C, the piezoresistive sensitivity and repeatability were almost unchanged when eliminating the effects by thermal exchanges. The water content of cementitious composites caused significant fluctuations on the resistivity and piezoresistivity, and the optimal water content for cement-based sensor possesses was found to be approximately 8%. Subjected to freeze-thaw cycles, dry CB/cementitious composites slightly reduced the piezoresistive sensitivity. However, the saturated composites presented dramatic piezoresistivity reduction by 30.7%, due to the microstructural damages caused by the volume expansion and shrinkage of pore solution. The related outcomes provide scientific framework for the adoption of CB/cementitious composites sensors for the SHM of concrete infrastructures under various environmental conditions.
Dong, W, Li, W, Shen, L & Sheng, D 2019, 'Piezoresistive behaviours of carbon black cement-based sensors with layer-distributed conductive rubber fibres', Materials & Design, vol. 182, pp. 108012-108012.
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© 2019 Conductive rubber fibres filled carbon black (CB)/cementitious composites were developed to achieve the cement-based sensors with excellent piezoresistivity in this study. Ameliorations on the conductivity and piezoresistive sensitivity of CB filled composites were mainly explored with conductive rubber fibres embedded. Their compressive strengths were investigated to evaluate the practical application possibility. The results indicated that the composites with CB content <4.0 wt% possessed acceptable compressive strengths. In terms of conductivity and piezoresistivity, both conductivity and piezoresistivity of composites filled with 0.5 wt% CB increased with the rubber content, and their gauge factor raised to 91 when embedded with 80 rubber fibres (1.27 vol%). Moreover, phenomenon of “piezoresistive percolation” was observed by sharp fractional changes of resistivity for the composites filled with 1.0 wt% CB, where existed highest gauge factor reaching 482 when embedded with same rubber fibres. However, because of the excellent conductivity of 2.0 wt% CB filled composites, the gauge factor firstly increased but then slightly decreased around 100 with increase of rubber fibre content. Overall, conductive rubber fibres can significantly improve the piezoresistivity of CB/cementitious composites by the increased gauge factor.
Dong, W, Li, W, Tao, Z & Wang, K 2019, 'Piezoresistive properties of cement-based sensors: Review and perspective', Construction and Building Materials, vol. 203, pp. 146-163.
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© 2019 Elsevier Ltd Cement-based sensors are increasingly used in smart concrete to self-sense and monitor the damages and cracks through the measurements of concrete electrical resistivity. The fundamental concepts, key components, manufacturing process, piezoresistivity measurements, and primary applications of cement-based sensors are reviewed in this paper. Various materials, mechanical and environmental factors affecting concrete piezoresistive properties are explicated. Some contradictory results from different studies are reported and discussed. Future perspectives of piezoresistive cement-based sensors are also delineated. The review reveals that there is an optimal conductor content, below which the sensor would perform more like plain concrete with high resistivity and low sensitivity, while excessively higher than which, the dispersion of the conductive phase could become difficult, thus increasing resistivity. The manufacturing process, such as the dispersion method of conductors and curing condition, plays a significant role in conductor distribution, matrix density and pore structure of the sensors, which, together with rheology of the sensor composite, consequently alters the piezoresistive properties of the sensors. In addition to responding to mechanical loading, cement-based piezoresistive sensor also has a great potential for monitoring behaviour of concrete under freeze-thaw cycling. It is expected that this review will provide not only an orientation for new researchers to explore and engage in related studies but also an insight for experienced researchers to perform transformational examinations into cement-based piezoresistive sensors.
Fang, J, Wu, C, Li, J, Liu, Q, Wu, C, Sun, G & Li, Q 2019, 'Phase field fracture in elasto-plastic solids: Variational formulation for multi-surface plasticity and effects of plastic yield surfaces and hardening', International Journal of Mechanical Sciences, vol. 156, pp. 382-396.
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© 2019 Elsevier Ltd The phase field modelling has been extended from brittle fracture to ductile fracture by incorporating plasticity. However, the effects of plastic yield functions and hardening on the fracture behaviour have not been examined systematically to date. The phase field fracture coupled with multi-surface plasticity is formulated in the variational framework for the unified yield criterion, which is able to facilitate the study on different yield surfaces. First, the homogeneous solutions of fracture in elasto-plastic solids are derived analytically for 1D and 2D cases. The results show that a greater hardening modulus would lead to an ascending branch of the stress versus strain curve; and the yield function may significantly affect the stress state and phase field damage. Second, the finite element (FE) technique is implemented for modelling the phase field fracture in elasto-plastic solids, in which the stress update and consistent tangent modular matrix are derived for the unified yield criterion. Finally, three numerical examples are presented to explore the effects of the yield function and material hardening. It is found that the yield function and material hardening could significantly affect the crack propagation and the final fracture pattern. In particular, the Tresca yield function tends to create a straight crack path orthogonal to the first principal stress, while the other yield functions show no sizeable difference in their crack paths.
Fang, J, Wu, C, Liu, Q, Sun, G & Li, Q 2019, 'Implicit Integration of the Unified Yield Criterion in the Principal Stress Space', Journal of Engineering Mechanics, vol. 145, no. 7, pp. 04019041-04019041.
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© 2019 American Society of Civil Engineers. An implicit numerical integration algorithm is presented for the unified yield criterion, which could encompass most other yield criteria. The modification matrix, which is used to convert the continuum tangent modular matrix into the consistent tangent modular matrix, is derived for the return to planes, lines, and the apex of the unified yield criterion with multisurface plasticity with discontinuities. The stress update and consistent tangent modular matrix are first derived in closed form in the principal stress space, and then they are transformed back into the general stress space by coordinate transformation. Three numerical examples are used to demonstrate the effectiveness of the presented algorithm. The correctness of the developed algorithm is validated by the analytical solution and ABAQUS solution with the built-in Mohr-Coulomb model. The developed algorithm is also demonstrated to be least twice more efficient than the ABAQUS built-in algorithm. The presented algorithm for the unified yield criterion can facilitate the understanding of the effect the intermediate principal stress. With the increase in b, the force versus deflection curve at the midspan increases for the beam under three-point bending, and the critical radius of the elastoplastic interface decreases (i.e., the plastic zone becomes small) for the circular tunnel under hydrostatic pressure.
Fang, J, Wu, C, Rabczuk, T, Wu, C, Ma, C, Sun, G & Li, Q 2019, 'Phase field fracture in elasto-plastic solids: Abaqus implementation and case studies', Theoretical and Applied Fracture Mechanics, vol. 103, pp. 102252-102252.
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© 2019 Elsevier Ltd Phase field modelling for fracture has been extended from elastic solids to elasto-plastic solids. In this study, we present the implementation procedures of a staggered scheme for phase field fracture of elasto-plastic solids in commercial finite element software Abaqus using subroutines UEL and UMAT. The UMAT is written for the constitutive behaviour of elasto-plastic solids, while the UEL is written for the phase field fracture. The phase field and displacement field are solved separately using the Newton-Raphson iteration method. In each iteration, one field is computed by freezing the other field at the last loading increment. A number of benchmark examples are tested from one single element up to 3D problems. The correctness of the staggered scheme is verified analytically in terms of the stress-strain curve and the evolution of the phase field in the one single element example. In the 2D and 3D problems, the fracture behaviour of elasto-plastic solids can be reproduced in terms of reaction force curve and crack propagation, which exhibit good agreement with the experimental observations and numerical results in literature. Not only can the proposed implementation help attract more academic researchers, but also engineering practitioners to take the advantages of phase field modelling for fracture in elasto-plastic solids. The Abaqus subroutine codes can be downloaded online from Mendeley data repository linked to this work (The link is provided in Supplementary material).
Fatahi, B 2019, 'Editorial', Proceedings of the Institution of Civil Engineers - Ground Improvement, vol. 172, no. 1, pp. 1-2.
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Gao, H, Liu, Z, Yang, Y, Wu, C & Geng, J 2019, 'Blast-resistant performance of aluminum foam-protected reinforced concrete slabs', Baozha Yu Chongji/Explosion and Shock Waves, vol. 39, no. 2.
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n order to study the blast-resistant protective effect of the aluminum foam slab as porous energy absorbing material on the engineering structure, using an outdoor explosion test, the dynamic response and failure modes of reinforced concrete (RC) slabs with different aluminum foam protective layers under blast loading were studied, and the finite element model was established by using the LS-DYNA software. Through comparison with the test, the feasibility of the model was verified. The dynamic responses of RC slabs with or without aluminum foam protective layers were compared and analyzed, and the effects of aluminum foam density gradient distribution and longitudinal reinforcement ratio were analyzed. The results show that the finite element model can accurately describe the dynamic response of RC slabs with aluminum foam protective layers. Aluminum foam protective layers can effectively reduce the deflection of reinforced concrete slabs and reduce the damage of specimens. The aluminum foam density increases from bottom to top, which has the best blast-resistant performance on RC slabs. Moreover, increasing the reinforcement ratio can improve the blast-resistant performance of aluminum foam-protected RC slabs.
Gowripalan, N, Cao, J, Sirivivatnanon, V & South, W 2019, 'Accelerated autoclave test for determining alkali silica reaction of concrete', Concrete in Australia, vol. Volume 45, no. No 2, pp. 37-40.
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Alkali silica reaction (ASR) in concrete is a deleterious reaction which occurs due to the reaction between alkalis in the pore solution and reactive forms of silica found in some aggregates. ASR results in expansion and cracking which reduce the mechanical properties of the concrete. An ultra-accelerated autoclave test method has been used to test concrete prisms with and without alkali boosting. In this method, expansion and deterioration caused by ASR in concrete was investigated using an autoclave to simulate long-term deterioration. Test parameters such as temperature, pressure, duration of autoclaving and alkali boosting were investigated. Results obtained within a short period, clearly show large expansions and deterioration levels for concrete made with reactive aggregates.
Gowripalan, N, Nguyen, T, Yang, Y, Li, J & Sirivivatnanon, V 2019, 'Evaluation of elastic modulus reduction due to ASR', Concrete in Australia, vol. 45, no. 2, pp. 47-52.
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Evaluation of reduction in modulus of elasticity of concrete undergoing alkali silica reaction is carried out using an artificial neural network
Gu, X, Yu, Y, Li, Y, Li, J, Askari, M & Samali, B 2019, 'Experimental study of semi-active magnetorheological elastomer base isolation system using optimal neuro fuzzy logic control', Mechanical Systems and Signal Processing, vol. 119, pp. 380-398.
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© 2018 Elsevier Ltd In this paper, a “smart” base isolation strategy is proposed in this study utilising a semi-active magnetorheological elastomer (MRE) isolator whose stiffness can be controlled in real-time and reversible fashion. By modulating the applied current, the horizontal stiffness of the MRE isolator can be controlled and thus the control action can be generated for the isolated structure. To overcome the inherent nonlinearity and hysteresis of the MRE isolator, radial basis function neural network based fuzzy logic control (RBF-NFLC) was developed due to its inherent robustness and capability in coping with uncertainties. The NFLC was optimised by a non-dominated sorting genetic algorithm type II (NSGA-II) for better suited fuzzy control rules as well as most appropriate parameters for the membership functions. To evaluate the effectiveness of the proposed smart base isolation system, four scenarios are tested under various historical earthquake excitations, i.e. bare building with no isolation, passive isolated structure, MRE isolated structure with Bang-Bang control, MRE isolated structure with proposed NFLC. A three-storey shear building model was adopted as the testing bed. Through the testing results, limited performance of passive isolation system was revealed. In contrast, the adaptability of the proposed isolation strategy was demonstrated and it is proven that the smart MRE base isolation system is able to provide satisfactory protection for both structural and non-structural elements of the system over a wide range of hazard dynamic loadings.
Ha, Q & Phung, MD 2019, 'IoT‐enabled dependable control for solar energy harvesting in smart buildings', IET Smart Cities, vol. 1, no. 2, pp. 61-70.
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Ha, QP, Yen, L & Balaguer, C 2019, 'Robotic autonomous systems for earthmoving in military applications', Automation in Construction, vol. 107, pp. 102934-102934.
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© 2019 Elsevier B.V. Along with increasing innovations in frontier engineering sciences, the advancement in Robotic Autonomous Systems (RAS) has brought about a new horizon in earthmoving processes for construction. In the military domain, there is also an increasing interest in utilising RAS technologies. In particular, ground-based forces are frequently called upon to conduct earthmoving tasks as part of military operations, tasks which could be partially or fully aided by the employment of RAS technologies. There have been rapid developments in military construction automation using high-mobility ground-based platforms, human-machine and machine-machine interfaces, teleoperation and control systems, data transmission systems, machine perception and manipulation capabilities, as well as advances in networked robotics and cyberphysical systems. Given these developments it is timely to undertake a comprehensive overview on the topic of interest to the research community and the authority. This paper presents an overview of the RAS development for platform-centric earthworks together with an analysis of the technical feasibility, maturity, key technical challenges, and future directions for the application of RAS technologies to earthmoving tasks of interest to the army.
Hassoun, M & Fatahi, B 2019, 'Novel integrated ground anchor technology for the seismic protection of isolated segmented cantilever bridges', Soil Dynamics and Earthquake Engineering, vol. 125, pp. 105709-105709.
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© 2019 Elsevier Ltd An external restraining system which is anchoring the bridge superstructure to the embankment backfill is proposed in this study for the seismic protection of isolated bridges. The restraining system is employed to reduce the seismic demands of the bridge deck by utilising the otherwise inactive ground behind the abutment back-walls. The system can be described as fastening the bridge end-diaphragms to the rocky strata that lie beneath the abutment backfill. The anchoring is achieved through a series of steel strands grouted to the rock to achieve a strong anchoring capacity. Indeed, the proposed anchor is flexible enough to allow the thermal, creep and shrinkage serviceability movements of the deck. A parametric study conducted in this paper shows that the ground anchor external restraining system is truly effective in reducing the seismic demands of the bridge deck.
He, L-X, Wu, C & Li, J 2019, 'Post-earthquake evaluation of damage and residual performance of UHPSFRC piers based on nonlinear model updating', Journal of Sound and Vibration, vol. 448, pp. 53-72.
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© 2019 Elsevier Ltd This paper presents an innovative approach for damage and residual performance evaluation of ultra-high performance steel fiber reinforced concrete (UHPSFRC) piers after earthquakes utilizing low-level vibration tests. A nonlinear fiber section element model is constructed in OpenSees to simulate the hysteretic behavior of a UHPSFRC bridge pier. Experimental data from a UHPSFRC column is utilized to verify the accuracy of the nonlinear numerical model. Based on the nonlinear fiber section element model, a new technique of nonlinear finite element model updating involving two updating stages is developed. This new method is designed to incorporate the maximum and minimum strains of section fibers as the updating parameters. By forming the objective function from the modal information, the damage parameters related to the nonlinear material model can be updated by solving the constrained optimization problem. To validate the efficiency of this updating approach, it has been applied to a numerically simulated UHPSFRC pier. With using the updated nonlinear finite element model, the residual axial loading capacity and post-seismic performance of the UHPSFRC pier are examined. The numerical results indicate that the updated nonlinear finite element model can be used not only to assess the current damage state of the UHPSFRC pier but also to predict its future performance after an earthquake. Finally, the noise effect on the proposed method is also investigated. The results reveal that the post-earthquake evaluation approach for UHPSFRC piers based on this study's updating algorithm is robust to noise.
Hu, Y, Tang, Z, Li, W, Li, Y & Tam, VWY 2019, 'Physical-mechanical properties of fly ash/GGBFS geopolymer composites with recycled aggregates', Construction and Building Materials, vol. 226, pp. 139-151.
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© 2019 Elsevier Ltd The properties of fly ash and ground granulated blast furnace slag (GGBFS) combination based geopolymer composites containing recycled aggregate are investigated in this study, which obtained from construction and demolition wastes. The effects of recycled aggregate replacement and GGBFS inclusion on the physical and mechanical properties of geopolymer composites were investigated in this study. The scanning electron microscopic (SEM) were conducted to provide a thorough insight into the characterization of microstructures. The results reveal that using recycled aggregate has an insignificant impact on workability and setting time, while it causes a reduction in physical and mechanical properties. The inclusion of GGBFS reduces workability and setting time. However, improved physical and mechanical properties can be achieved in the geopolymer composites after the incorporation of GGBFS, and this effect is more prominent in the geopolymer composites containing recycled aggregates. The water absorption and sorptivity exhibit a strong correlation with the volume of permeable voids of geopolymer composites. Besides, very good relationships were established between the compressive strength and other mechanical properties, and these relationships fitted reasonably well with the other predictions.
Huang, L, Liu, Z, Wu, C & Liang, J 2019, 'The scattering of plane P, SV waves by twin lining tunnels with imperfect interfaces embedded in an elastic half-space', Tunnelling and Underground Space Technology, vol. 85, pp. 319-330.
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© 2018 Elsevier Ltd A viscous-slip interface model is employed to simulate the contact between the tunnels lining and the surrounding rock, and the scattering of P, SV waves by twin shallowly buried lining tunnels is investigated with the indirect boundary integral equation method (IBIEM). The amplification effect of the dynamic stress concentration of the lining and the surface displacement near the tunnels is examined. It is evident that the slipping-stiffness coefficient and viscosity coefficient at the lining-surrounding rock interface have a significant influence on the dynamic stress distribution and the nearby surface displacement response of the lining tunnel, while the influence characteristics strongly depend on the incident wave type, frequency and angle. Under the incidence of low frequency wave, as a whole, with the increase of the sliding stiffness, the hoop stress increases gradually for plane P and SV waves; while in the resonance frequency (the incident wave frequency is consistent with the natural frequency of the soil column above the tunnels), specially for high-frequency band, the dynamic stress concentration effect is more significant for smaller sliding stiffness. With the increase of viscosity coefficient, the dynamic stress concentration factor inside the lining gradually decreases. Also, the tunnels with viscous-slip interfaces have a more significant amplification effect on the nearby surface displacement amplitude. Moreover, the hoop stress of the twin tunnels may be obviously larger than that of single tunnel in most cases. The dynamic analysis of the underground structure under the actual strong dynamic loading should consider the influence of the slip effect between the lining and surrounding rock interface.
Jahandari, S, Saberian, M, Tao, Z, Mojtahedi, SF, Li, J, Ghasemi, M, Rezvani, SS & Li, W 2019, 'Effects of saturation degrees, freezing-thawing, and curing on geotechnical properties of lime and lime-cement concretes', Cold Regions Science and Technology, vol. 160, pp. 242-251.
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© 2019 Elsevier B.V. There are very limited researches carried out to investigate the influence of saturation degrees, freezing-thawing, and curing times on geotechnical properties of lime concrete (LC) and lime-cement concrete (LCC) due to the capillary action and changes in groundwater table. Subsequently, the primary goal of this research is to investigate the influence of these parameters on mechanical properties of LC and LCC using unconfined compression tests, namely uniaxial compressive strength (UCS), stress-strain behavior, deformability index (I D ), secant modulus (E S ), failure strain, bulk modulus (K), resilient modulus (M R ), brittleness index (I B ), and shear modulus (G). At first, the mechanical and chemical characteristics of the utilized materials were measured. Then, samples were made with an optimal amount of cement, lime, coarse-grained soil, fine-grained soil, and water. The samples were then exposed to saturation points extending from 0 to 100% after 14, 28, 45 and 60 curing days. Then, to consider the effect of amount of saturation on the mechanical properties, UCS tests were performed on some of the samples. Other LCC specimens were exposed to freezing-thawing conditions to consider the effect of this phenomenon on the mechanical properties as well. The results of more than 250 UCS tests demonstrated that the curing times significantly affected the strength of LC and LCC specimens. Moreover, it is not ideal and logical to utilize LC and LC columns at a profundity underneath or near the groundwater level, though it is reasonable to adopt LCC and LCC columns at a profundity beneath or near the groundwater level because of the immaterial effect of degrees of saturation on LCC. In addition, this study showed that extending the curing period and diminishing the saturation degree would increase the strength and mechanical properties of the LCC specimens. The results of freezing-thawing demonstrated a negligible increase in the stre...
Jamshidi Chenari, R, Alaie, R & Fatahi, B 2019, 'Constrained Compression Models for Tire-Derived Aggregate-Sand Mixtures Using Enhanced Large Scale Oedometer Testing Apparatus', Geotechnical and Geological Engineering, vol. 37, no. 4, pp. 2591-2610.
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© 2018, Springer Nature Switzerland AG. Tire derived aggregates have recently been in wide use both in industry and engineering applications depending on the size and the application sought. Five different contents of tire derived aggregates (TDA) were mixed with sand thoroughly to ensure homogeneity. A series of large scale oedometer experiments were conducted to investigate the compressibility properties of the mixtures. Tire shreds content, TDA aspect ratio, skeletal relative density and overburden pressure are studied parameters. Constrained deformation modulus and coefficient of earth pressure at rest are measured parameters. All tests were conducted at seven overburden pressure levels. It was concluded that deformability of TDA-sand mixture increases with soft inclusion. Overburden pressure and skeletal relative density are also important parameters which render more rigidity and less lateral earth pressure coefficient accordingly. TDA size or aspect ratio was shown to have minor effect at least for the constrained strain conditions encountered in current study. An EPR-based parametric study and also sensitivity analyses based on cosine amplitude method revealed quantitative evaluation of the relative importance of each input parameter in varying deformation and lateral earth pressure coefficient as the outputs.
Jiang, Y & Nimbalkar, S 2019, 'Finite Element Modeling of Ballasted Rail Track Capturing Effects of Geosynthetic Inclusions', Frontiers in Built Environment, vol. 5.
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© 2019 Jiang and Nimbalkar. This paper presents a two dimensional finite element (FE) approach to investigating beneficial aspects of geogrids in the railway track. The influences of different factors including the subgrade strength, the geogrid stiffness, the placement depth of geogrid, the effective width of geogrid, the strength of ballast-geogrid interface and the combination of double geogrid layers were investigated under the monotonic loading. The results indicated the role of geogrid reinforcement is more pronounced over the weak compressible subgrade. A stiffer geogrid reduces ballast settlement and produces a more uniform stress distribution along a track. The placement location of a geogrid is suggested at the ballast-sub-ballast interface to achieve better reinforcement results. Although the width of a geogrid layer should be sufficient to cover an entire loaded area, excessive width does not guarantee additional benefits. Higher interface strength between a ballast and a geogrid is beneficial for effective reinforcement. Increasing the number of geogrid layers is an effective way to reinforce the ballast over weak subgrades. The results of the limited cyclic FE simulations revealed the consistency of the reinforcement effect of the geogrids under monotonic and cyclic loads.
Khabbaz, H, Gibson, R & Fatahi, B 2019, 'Effect of constructing twin tunnels under a building supported by pile foundations in the Sydney central business district', Underground Space, vol. 4, no. 4, pp. 261-276.
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© 2019 Tongji University and Tongji University Press In congested cities such as Sydney, competition for underground space escalates within the built environment because various assets require finite geotechnical strength and support. Specific problems such as damage to buildings may develop when high-rise buildings on piled foundations are subject to ground movements as tunnels are constructed. This paper focuses on the risks of tunneling beneath Sydney's Martin Place and how buildings are subject to additional loads caused by tunneling. The key objective of this study is to improve the understanding of tunnel–rock–pile interactions and to encourage sustainable development. A finite element model is developed to predict the interaction between tunnel construction and piled foundations. The tunnel, rock, and pile components are studied separately and are then combined into a single model. The ground model is based on the characteristics of Hawkesbury Sandstone and is developed through a desktop study. The piles are designed using Australian Standards and observations of high-rise buildings. The tunnel construction is modeled based on the construction sequence of a tunnel boring machine. After combining the components, a parametric study on the relationship between tunnel location, basements, and piles is conducted. Our findings, thus far, show that tunneling can increase the axial and flexural loads of piles, where the additional loading exceeds the structural capacity of some piles, especially those that are close to basement walls. The parametric study reveals a strong relationship between tunnel depth and lining stresses, while the relationship between tunnel depth and induced pile loads is less convincing. Furthermore, the horizontal tunnel position relative to piles shows a stronger relationship with pile loads. Further research into tunnel–rock–pile interactions is recommended, especially beneath basements, to substantiate the results of this study.
La, HM, Dinh, TH, Pham, NH, Ha, QP & Pham, AQ 2019, 'Automated robotic monitoring and inspection of steel structures and bridges', Robotica, vol. 37, no. 5, pp. 947-967.
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SummaryThis paper presents visual and 3D structure inspection for steel structures and bridges using a developed climbing robot. The robot can move freely on a steel surface, carry sensors, collect data and then send to the ground station in real-time for monitoring as well as further processing. Steel surface image stitching and 3D map building are conducted to provide a current condition of the structure. Also, a computer vision-based method is implemented to detect surface defects on stitched images. The effectiveness of the climbing robot's inspection is tested in multiple circumstances to ensure strong steel adhesion and successful data collection. The detection method was also successfully evaluated on various test images, where steel cracks could be automatically identified, without the requirement of some heuristic reasoning.
Li, CY, Chen, SJ, Li, WG, Li, XY, Ruan, D & Duan, WH 2019, 'Dynamic increased reinforcing effect of graphene oxide on cementitious nanocomposite', Construction and Building Materials, vol. 206, pp. 694-702.
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© 2019 The reinforcing effect of graphene oxide on cementitious materials under high strain rate remains largely unknown. Existing studies on microfiber reinforced cementitious composites showed that the dynamic increase factor (DIF) decreases due to these fibres. This study reports that the reinforcing effect of graphene oxide nanosheets can, in contrast, increase with strain rate. Tensile splitting and compression tests were conducted under both static and dynamic loadings. High strain rate, up to 1700 s −1 , is achieved using a split Hopkinson pressure bar apparatus. It is found that the DIF of graphene oxide nanocomposite only increase when the DIF is higher than a threshold which is about 780 and 30 s −1 for compression and tensile test respectively. The increased of DIF was correlated with the speed of crack development and pull-out of the graphene oxide nanosheets. Also, the pull-out or fracture of graphene oxide on fragmented sand was also found a possible contributing factor to the increased DIF. The findings of this study indicate the future potential of atomic-thin nanosheets for materials under extreme impact and blast loading.
Li, Y & Li, J 2019, 'Overview of the development of smart base isolation system featuring magnetorheological elastomer', Smart Structures and Systems, vol. 24, no. 1, pp. 37-52.
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Despite its success and wide application, base isolation system has been challenged for its passive nature, i.e., incapable of working with versatile external loadings. This is particularly exaggerated during near-source earthquakes and earthquakes with dominate low-frequency components. To address this issue, many efforts have been explored, including active base isolation system and hybrid base isolation system (with added controllable damping). Active base isolation system requires extra energy input which is not economical and the power supply may not be available during earthquakes. Although with tunable energy dissipation ability, hybrid base isolation systems are not able to alter its fundamental natural frequency to cope with varying external loadings. This paper reports an overview of new adventure with aim to develop adaptive base isolation system with controllable stiffness (thus adaptive natural frequency). With assistance of the feedback control system and the use of smart material technology, the proposed smart base isolation system is able to realize real-time decoupling of external loading and hence provides effective seismic protection against different types of earthquakes.
Liang, X, Wu, C, Yang, Y & Li, Z 2019, 'Experimental study on ultra-high performance concrete with high fire resistance under simultaneous effect of elevated temperature and impact loading', Cement and Concrete Composites, vol. 98, pp. 29-38.
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© 2019 Fire is a big risk to buildings and structures, posing a great threat to human lives. In this study, a newly developed ultra-high performance concrete (UHPC) was investigated experimentally. Quasi-static compression tests were conducted after the UHPC was first exposed to a high temperature, i.e. 200, 400, 600, 800 or 1000 °C, and then cooled down to room temperature, while dynamic tests were carried out under combined effect of a high temperature, i.e. 200, 400, 600, or 800 °C, and impact loading. The dynamic tests were done both at high temperatures and after cooling down and comparisons were made between these two scenarios. Based on the tests on this UHPC, mechanical and physical characteristics under the combined effect were studied. Besides, explosive spalling was analysed. It was interesting to find polypropylene (PP) fibre could play a negative role in preventing explosive spalling between 320 and 380 °C.
Liang, X, Wu, C, Yang, Y, Wu, C & Li, Z 2019, 'Coupled effect of temperature and impact loading on tensile strength of ultra-high performance fibre reinforced concrete', Composite Structures, vol. 229, pp. 111432-111432.
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© 2019 Elsevier Ltd This study focused on coupled effect of temperature and impact loading on tensile strength of an ultra-high performance fibre reinforced concrete (UHPFRC), which retains 69% of its original compressive strength after exposure to 1000 °C. The relationship between tensile strength and compressive strength was investigated under the coupled action since temperature may have different effects on them. Static tests and dynamic tests using a self-designed Split Hopkinson Pressure Bar (SHPB) system were conducted at temperatures 20, 200, 400, 600 and 800 °C. Comparison was made between tensile strength and compressive strength of UHPFRC obtained in hot state and cooled-down state. It was found splitting tensile strength fell sharply beyond 400 °C but still retained 41% of its original strength at 800 °C, well above other concretes. Temperature and combined action of elevated temperature and impact loading have different effects on splitting tensile strength and compressive strength.
Lin, X, Far, H & Saleh, A 2019, 'Structural Behaviour and Mechanical Properties of Welded Steel I-Girders with Corrugated Webs', International Journal of Steel Structures, vol. 19, no. 4, pp. 1342-1352.
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© 2019, Korean Society of Steel Construction. Steel I girders with corrugated webs are appropriate alternatives for normal flat-web girders in steel structures since they provide lighter and smaller beam features in steel design. Based on the existing literature, the corrugated web beams (CWBs) provide many advantages for structural applications. In this study, a series of numerical analyses have been performed in order to investigate the structural behaviour of steel I girders with corrugated web profile and to compare their mechanical performance with normal welded beams. Theory of Ultimate Limit State design has been adopted in accordance with AS4100 (Steel structures, Standard Australia, Sydney, 1998) along with considering geometric and material non-linearity in the numerical analyses in SAP2000. Comparing the results of the numerical investigation, merits of using corrugated welded beams (CWBs) over normal welded beams (WBs) have become apparent. Moreover, investigations regarding force–displacement relationship and buckling analysis of the webs were carried out and presented to further validate the advantages of using corrugated web beams. CWBs have been used in some parts of Australia without detailed information about their mechanical properties. Thus, based on the outcomes of this study, CWB table for dimensions and cross sectional properties has been developed and proposed for practical applications.
Ling, Y, Wang, K, Li, W, Shi, G & Lu, P 2019, 'Effect of slag on the mechanical properties and bond strength of fly ash-based engineered geopolymer composites', Composites Part B: Engineering, vol. 164, pp. 747-757.
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© 2019 Recently, the concept of engineered cementitious composites (ECCs) has been extended to the creation of engineered geopolymer composites (EGCs). Although showing similar mechanical characteristics (e. g., strain hardening and multiple cracking) to conventional ECC, the strength of existing EGC is generally low, and this sometimes restrains its applications. In the present study, a low-calcium (Class F) fly ash-based, polyvinyl alcohol (PVA) fiber reinforced EGC was developed and further modified by a ground-granulated blast-furnace slag (slag). The slag was used to replace the fly ash at content of 0%, 10%, 20%, and 30% (by weight). The effects of the slag on the mechanical properties (e.g., compressive strength, modulus of elasticity, uniaxial tensile behavior, flexural bending strength, and pullout bond strength) of the EGCs were investigated. The results revealed that all EGCs studied exhibited a strain/deflection hardening behavior under tension/flexure, and all slag replacements for fly ash enhanced strength-related properties but reduced ductility-related properties of the EGCs. The EGC mix with 20% slag replacement for fly ash (FA-20%S) had 102.3 MPa compressive strength, 6.8 MPa tensile strength, and 6.2 MPa bond strength, while the EGC mix with no slag (FA-0%S) had 72.6 MPa compressive strength, 4.7 MPa tensile strength, and 3.5 MPa bond strength at 28 days. These strength enhancements were mainly attributed to the improved density of the EGC matrix and the bond between the matrix and fiber. There are close relationships between the bond strength and other strengths, especially the tensile and flexural strengths, of the EGCs.
Liu, J, Wu, C, Li, C, Dong, W, Su, Y, Li, J, Cui, N, Zeng, F, Dai, L, Meng, Q & Pang, J 2019, 'Blast testing of high performance geopolymer composite walls reinforced with steel wire mesh and aluminium foam', Construction and Building Materials, vol. 197, pp. 533-547.
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© 2018 Elsevier Ltd Two blast tests were conducted to study the blast resistance of high performance geopolymer composite walls reinforced with steel wire mesh (SWM) and aluminium foam (AF). Conventional reinforced concrete (CRC) walls were also tested as control specimens. In total seven walls were tested under different blast loading conditions. The first blast test was conducted on one 2260 mm × 2260 mm × 150 mm SWM reinforced, one 2260 mm × 1000 mm × 150 mm SWM reinforced and one 2260 mm × 1000 mm × 150 mm combined SWM and AF reinforced high performance geopolymer composite walls under 50 kg TNT explosives at a standoff distance of 2.3 m. The second blast test was conducted on one 2260 mm × 2260 mm × 150 mm SWM reinforced and one 2260 mm × 2260 mm × 150 mm combined SWM and AF reinforced high performance geopolymer composite walls under 100 kg TNT explosives on the ground at the same standoff distance. Blast tests were also performed on two 2260 mm × 2260 mm × 150 mm CRC walls under such two designed explosions to compare their behaviours with reinforced high performance geopolymer composite walls. LVDT (linear variable differential transformer) devices were used to record the deflection histories and pressure sensors were used to measure the airblast pressure histories. The testing results indicated that the combined SWM and AF reinforced high performance geopolymer composite walls had a better blast resistance than the CRC walls, and the SWM reinforced high performance geopolymer composite wall was superior to both.
Liu, J, Wu, C, Li, J, Fang, J, Su, Y & Shao, R 2019, 'Ceramic balls protected ultra-high performance concrete structure against projectile impact–A numerical study', International Journal of Impact Engineering, vol. 125, pp. 143-162.
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© 2018 Elsevier Ltd Ceramic materials have excellent mechanical properties such as light weight, great hardness and high compressive strength. In this paper, a numerical study is conducted to investigate the response of ceramic balls protected ultra-high performance concrete (UHPC) targets against the high-velocity rigid projectile impact using the coupled smoothed particle hydrodynamics-finite element (SPH-FE) method in LS-DYNA. Based on the validated numerical models, parametric studies are performed to explore the effect of diameter, spatial arrangement and material type of ceramic balls as well as the impact position on the dynamic performance of UHPC targets, and then perforation and ballistic limits of ceramic balls protected UHPC targets are obtained. Compared with other UHPC slabs at the striking velocities from 500 m/s to 850 m/s, UHPC slabs protected with 6-layer hex-pack arranged ceramic balls with the diameter of 20 mm is most effective in terms of reducing the depth of penetration (DOP). In addition, the utilization of ceramic balls is economical in protective structures since the damaged ceramic balls can be replaced and undamaged ceramic balls are reusable.
Liu, Z, Huang, L, Liang, J & Wu, C 2019, 'A three-dimensional indirect boundary integral equation method for modeling elastic wave scattering in a layered half-space', International Journal of Solids and Structures, vol. 169, pp. 81-94.
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© 2019 A new indirect boundary integral equation method (IBIEM)is proposed in this study to solve three-dimensional (3-D)elastic wave scattering by heterogeneities in a multi-layered half-space, employing Green's function of distributed loads on equivalent circular elements, thus avoiding the element discretization on layer interfaces. The proposed method enables the fictitious loads to be directly distributed on the surfaces of scatterer and the weak singularity to be tackled by analytical integration. Also, the radiation condition in the semi-infinite layered medium can be satisfied accurately, and the memory requirements can also be greatly reduced, especially for a large number of layers or gradient medium. The numerical accuracy was verified through comparisons with existing results and the numerical convergence was also confirmed. The results clearly demonstrate the simplicity and effectiveness of the method, and also reveals the complicated scattering characteristics in a layered half-space that are dominated by the resonant properties of the layered medium.
Liu, Z, Zhang, H, Cheng, A, Wu, C & Yang, G 2019, 'Seismic Interaction between a Lined Tunnel and a Hill under Plane SV Waves by IBEM', International Journal of Structural Stability and Dynamics, vol. 19, no. 02, pp. 1950004-1950004.
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This paper investigates the dynamic interaction between a lined tunnel and a hill under plane SV waves using the indirect boundary element method (IBEM), with the displacement and stress characteristics of the system presented in frequency domain. The IBEM has several unique advantages such as reducing calculation dimension, automatically satisfying the infinite radiation condition, etc. The numerical results indicated that the dynamic response of the tunnel–hill system is strongly dependent on incident wave characteristics, geometrical and material properties of the lined tunnel, as well as the topography of the hill. For a dimension ratio between the hill and tunnel of less than 10.0, the lined tunnel has large amplification or deamplification effect on the dynamic response of the hill. Correspondingly, the hill also greatly amplifies the displacement and stress concentration of the tunnel especially in the lower-frequency range, due to the complicated interference effect among the reflected waves and diffracted waves induced by the tunnel and hill. Also demonstrated is that the displacement and stress amplitude spectrums highly depend on the incident frequency and the space location, and there exist multiple peaks and troughs in the spectrum curve with the peaks usually appearing in the low-frequency range. Thus, for the seismic safety assessment of a hill slope or hill tunnel in practice, the dynamic interaction within the tunnel–hill system should be taken into consideration.
Long, G, Li, L, Li, W, Ma, K, Dong, W, Bai, C & Zhou, JL 2019, 'Enhanced mechanical properties and durability of coal gangue reinforced cement-soil mixture for foundation treatments', Journal of Cleaner Production, vol. 231, pp. 468-482.
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© 2019 Elsevier Ltd High-speed railways with high load capacity and long-term performance have been developed by the aid of high-performance construction materials for foundation treatments. The mechanical properties and durability of new cement-soil mixture reinforced by local sourced waste coal gangue aggregate were investigated in this study. Extensive experiments were carried out to analyse the effects of coal gangue on compressive strength, elastic modulus, stress-strain curve and anti-corrosion of cement-soil mixture. The results show that incorporation of coal gangue significantly improve the strength, stiffness and anti-corrosion ability of cement-soil mixture. Strength improvements up to 81.8% was achieved, but the ductile failure model shited to brittle failure with more than 42% coal gangue reinforcements. Except for the declining segment of the stress-strain curve, the ascending segment of the stress-strain curve can be fitted by the existing models. From the microstructural characterization, coal gangue can reduce acid solution permeation compared to the soil. For the cemented soil with coal gangue, the mass-loss rates only reach 4–7% after 140 days acid solution immersion. Therefore, this new clean production of high-performance cement-soil mixture through waste coal gangue reinforcement has great potential for railway foundation treatments.
Lu, Z-H, Li, H, Li, W, Zhao, Y-G, Tang, Z & Sun, Z 2019, 'Shear behavior degradation and failure pattern of reinforced concrete beam with chloride-induced stirrup corrosion', Advances in Structural Engineering, vol. 22, no. 14, pp. 2998-3010.
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Reinforcement corrosion exhibits an adverse effect on the shear strength of reinforced concrete structures. In order to investigate the effects of chloride-induced corrosion of reinforcing steel on the shear behavior and failure pattern of reinforced concrete beams, a total of 24 reinforced concrete beams with different concrete strength grades and arrangements of stirrups were fabricated, among which 22 beams were subjected to accelerated corrosion to achieve different degrees of reinforcement corrosion. The failure pattern, crack propagation, load–displacement response, and ultimate strength of these beams were investigated under a standard four-point loading test in this study. Extensive comparative analysis was conducted to investigate the effects of the concrete strength, shear span-to-depth ratio, and stirrup type on the shear behavior of the corroded reinforced concrete beams. The results show that increasing the stirrup yielding strength is more effective in improving the shear strength of corroded reinforced concrete beams than that of concrete compressive strength. In terms of three types of stirrups, the shear strength of the beams with deformed HRB-335 is least sensitive to stirrup corrosion, followed by the beams with smooth HPB-235 and the beams with deformed HRB-400. The effect of the different stirrups on the shear strength depends on the corrosion degree of stirrup and shear span-to-depth ratio of the beam. The predicted results of shear strength of corroded reinforced concrete beams by a proposed analytical model are well consistent with the experimental results.
Lu, Z-H, Lun, P-Y, Li, W, Luo, Z, Li, Y & Liu, P 2019, 'Empirical model of corrosion rate for steel reinforced concrete structures in chloride-laden environments', Advances in Structural Engineering, vol. 22, no. 1, pp. 223-239.
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The corrosion rate of reinforcing steel is an important factor to determine the corrosion propagation of reinforced concrete structures in the chloride-laden environments. Since the corrosion rate of reinforcing steel is affected by several coupled parameters, the efficient prediction of which remains challenging. In this study, a total of 156 experimental data on corrosion rate from the literature were collected and compared. Seven empirical models for predicting the corrosion rate were reviewed and investigated using the collected experimental data. Based on the investigations, a new empirical model is proposed for predicting the corrosion rate in corrosion-affected reinforced concrete structures considering parameters including concrete resistivity, temperature, relative humidity, corrosion duration and concrete chloride content. The comparison between the experimental data and those predicted using the new empirical model demonstrates that the new model gives a good prediction of the corrosion rate. Furthermore, the uncertainty and probability characteristics of these empirical models are also investigated. It is found that the probability distributions of the model errors can be described as lognormal, normal, Weibull or Gumbel distributions. As a result, the new empirical model can provide an efficient prediction of the corrosion rate of reinforcing steel, and the model error analysis results can be utilized for reliability-based service life prediction of reinforced concrete structures under chloride-laden environments.
Luo, Z, Li, W, Tam, VWY, Xiao, J & Shah, SP 2019, 'Current progress on nanotechnology application in recycled aggregate concrete', Journal of Sustainable Cement-Based Materials, vol. 8, no. 2, pp. 79-96.
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© 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group. As a very promising sustainable construction material, recycled aggregate concrete (RAC) has become a hot research topic and attracted wide attention. Although many investigations have been conducted, it is still a great challenge to product RAC with satisfactory and stable performance for practical engineering application. In recent years, nanotechnology has been introduced to RAC research and displayed distinct advantages over many traditional methods. This article is devoted to reviewing the current research on nanotechnology application in RAC, including nanoengineering and nanoscience. The corresponding results involving microstructure characteristics, mechanical properties, workability, and durability were summarized and discussed. It has been found that nanoscience has promoted better understanding of microstructure and various internal mechanism of RAC, while nanoengineering has helped RAC achieve dense microstructure, improved mechanical properties and durability. However, further efforts are required to realize the potential of nanotechnology and to bring breakthroughs in research and application of RAC.
Ma, J, Fan, F, Zhang, L, Wu, C & Zhi, X 2019, 'Effect of wave reflection on failure modes of single-layer reticulated domes subjected to interior blast loading', Engineering Failure Analysis, vol. 105, pp. 266-275.
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© 2019 Elsevier Ltd The single-layer reticulated dome is common in public structures, which suggests that this kind of building is a potential target of a terrorist attack. Once this structure is severely damaged in a terrorist attack, the people inside could be seriously injured. To avoid this situation, it is of great significance to investigate the failure mechanisms of the single-layer reticulated domes subjected to blast. In addition, shock waves from a blast converge and propagate in the internal space, leading to a nonuniform blast pressure field on the inner surface of the dome. The effects of reflected waves on failure modes of the dome were systematically investigated. A finite element model of a reticulated dome was created using ANSYS/LS-DYNA, where the code for blast loading that accounted for wave reflection was incorporated. Five failure modes were recognized and defined from 1050 simulations. Regularities in the distributions of failure modes were found. The effects of reflected waves on failure modes were analysed quantificationally.
Ma, J, Fan, F, Zhang, L, Wu, C & Zhi, X 2019, 'Experimental and Numerical Investigations of Pressure Field of Curved Shell Structure Subjected to Interior Blast', Shock and Vibration, vol. 2019, pp. 1-16.
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A terrorist attack on a long-span spatial structure would cause horrible results. Therefore, it is important to determine the characteristics of blast pressure fields to protect such structures. In this study, fully confined blast loading tests were conducted using a rigid curved shell model, which had an inner space similar to that of a reticulated dome. Four different scenarios were carried out to record the blast loading on five typical positions. The blast pressure-time data were compared and analyzed. In addition, a suitable numerical simulation method was proposed for the issues involved in interior blast loading. This numerical model was verified by comparing with the test data. A parametrical analysis of the interior blast simulations was conducted based on this numerical method. The blast loading values at specific positions were obtained with the key parameters varied within a reasonable scope. The blast loading from blast tests and simulations were presented. On this basis, the interior blast loading could conveniently be predicted by using the method and data in this paper, which could be used in the protective design of other reticulated domes.
Mahdavi, H, Fatahi, B & Khabbaz, H 2019, 'A comparison of frictional and socketed concrete injected columns in a transition zone', Geosynthetics International, vol. 26, no. 5, pp. 497-514.
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This paper sets out to investigate the options available for the transition from Concrete Injected Columns (CICs) to other ground improvement methods, used away from the bridge abutment. Two possible alternatives, widely spaced CICs socketed into stiff material and shorter, closely spaced, frictional CICs, were numerically simulated using FLAC3D software considering the dissipation of porewater pressure and variation of soil permeability with time. The total length of the CICs and the total volume of concrete used for their construction were the same for both alternatives. A geosynthetic layer was introduced into the load transfer platform, and interface elements were incorporated to simulate CIC-soil interaction. The numerical results were also compared with an established analytical solution and a good agreement was achieved. A comparison was then made between the two scenarios; indeed, the embankment on frictional CICs experienced less settlement on the surface, less loads in the geosynthetic, and the bending moments and shear forces generated in the columns were less than the corresponding values for socketed CICs. This study offers an enhanced understanding of the available options to practising engineers when designing road embankments on soft soil.
Maynard-Casely, HE, Booth, N, Leung, AE, Stuart, BH & Thomas, PS 2019, 'Potential of neutron powder diffraction for the study of solid triacylglycerols', Food Structure, vol. 22, pp. 100124-100124.
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© 2019 We present a high-resolution neutron powder diffraction study of the triclinic β form of tripalmitin as well as in situ crystallisation experiments, monitored with neutron diffraction, conducted over three different cooling rates. We use the results from the high-resolution study to anticipate if neutron diffraction could be beneficial in differentiating the polymorphism in triacylglycerol systems. We extend on this to present analysis of a diffraction pattern of cocoa butter, to establish the potential for neutron diffraction to study the (hydrogenous) forms of triacylglycerols used in food production.
Meena, NK & Nimbalkar, S 2019, 'Effect of Water Drawdown and Dynamic Loads on Piled Raft: Two-Dimensional Finite Element Approach', Infrastructures, vol. 4, no. 4, pp. 75-75.
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The piled raft foundations are widely used in infrastructure built on soft soil to reduce the settlement and enhance the bearing capacity. However, these foundations pose a potential risk of failure, if dynamic traffic loading and ground conditions are not adequately accounted in the construction phase. The ground conditions are complex because of frequent groundwater fluctuations. The drawdown of the water table profoundly influences the settlement and load sharing capacity of piled raft foundation. Further, the dynamic loading can also pose a potential risk to these foundations. In this paper, the two-dimensional finite element method (FEM) is employed to analyze the impact of water drawdown and dynamic loading on the stability of piled raft. The seismic response of piled raft is also discussed. The stresses and deformations occurring in and around the raft structure are evaluated. The results demonstrate that water drawdown has a significant effect on the stability and seismic response of piled raft. Various foundation improvement methods are assessed, such as the use of geotextile and increasing thickness of the pile cap, which aids of limiting the settlement.
Meng, Q, Wu, C, Su, Y, Li, J, Liu, J & Pang, J 2019, 'A study of steel wire mesh reinforced high performance geopolymer concrete slabs under blast loading', Journal of Cleaner Production, vol. 210, pp. 1150-1163.
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© 2018 Elsevier Ltd In this study, a novel green construction material, high performance alkali-activated geopolymer concrete is introduced. Both numerically and experimentally investigations were conducted on a new type of structural slabs made of steel wire mesh reinforced geopolymer concrete against close-in ground surface explosion. Steel rebar reinforced conventional concrete slabs are also studied to compare the results. The experimental investigation was conducted to study the slab damage mechanism. It is found that the steel wire mesh reinforced geopolymer concrete slab showed less damage and fragmentation under 50 kg Trinitrotoluene (TNT) blast load within 3 m, 5 m and 7 m distances as compared to the C30 concrete slab. Numerical analysis was then conducted to further investigate the slab dynamic responses. Combining the steel wire mesh reinforcement with geopolymer concrete can help increase the blast resistance capacity leading to promising and environmental friendly structural protective design.
Meng, Q, Wu, C, Su, Y, Li, J, Liu, J & Pang, J 2019, 'Experimental and numerical investigation of blast resistant capacity of high performance geopolymer concrete panels', Composites Part B: Engineering, vol. 171, pp. 9-19.
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© 2019 Elsevier Ltd In this study, the mechanical properties of a novel high performance alkali-activated geopolymer concrete under both static and dynamic loads were studied. The ground granulated blast-furnace slag powder (GGBS) and silica fume were used to manufacture this geopolymer concrete. Slabs that cast with this geopolymer concrete and steel wire mesh reinforcement were tested under close-in TNT explosion. The steel rebar reinforced C30 concrete slabs were tested as a control group. It is found that the steel wire mesh reinforced geopolymer concrete slabs achieved a more uniform strain distribution, which means a better structural performance against blast loadings as compared to the conventional C30 concrete slab under the same blast loads. The numerical investigation was then conducted to elaborate the test results.
Moghaddam, F, Sirivivatnanon, V & Vessalas, K 2019, 'The effect of fly ash fineness on heat of hydration, microstructure, flow and compressive strength of blended cement pastes', Case Studies in Construction Materials, vol. 10, pp. e00218-e00218.
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© 2019 In this paper, an experimental study on the effect of fly ash fineness on the heat of hydration, microstructure, flow and compressive strength of blended cement pastes was carried out and evaluated against control cement paste. Fly ashes with different fineness: classified fly ash, run-of-station fly ash and grounded run-of-station fly ash; with a median particle size of 17.4, 11.3 and 5.7 μm, respectively, from the same power station source in Australia were used to partially replace Portland cement at 20% and 40% by weight of cement using a fixed water-to-binder ratio of 0.40. Results of this study showed that the cumulative heat of hydration of blended cement paste decreased as fly ash content in blended cement paste was increased. For a given cement replacement level, blended cement paste containing finer fly ash released more heat of hydration when compared to coarser fly ash. Moreover, increasing the fineness of fly ash resulted in a higher consumption of calcium hydroxide at 7 and 28 days reflecting pozzolanic reactivity and, thus, a denser microstructure than blended pastes containing coarser fly ash as revealed by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and compressive strength results. In addition, the incorporation of fly ash in the blended pastes led to the introduction of an additional hydration peak in the heat evolution curve possibly due to the late activation of fly ash by calcium hydroxide renewing the C 3 A reaction and converting ettringite to monosulfate. The flow of the freshly blended cement pastes was also found to improve slightly with increasing fineness of the fly ash. In addition, the hardened blended cement pastes containing 20% ground run-of-station fly ash showed comparable compressive strength with the control cement pastes at both 7 and 28 days mainly due to the higher fineness of the ground run-of-station fly ash and increased reactivity compared to coarser grade fly ash.
Ngoc, TP, Fatahi, B & Khabbaz, H 2019, 'Impacts of Drying-Wetting and Loading-Unloading Cycles on Small Strain Shear Modulus of Unsaturated Soils', International Journal of Geomechanics, vol. 19, no. 8, pp. 04019090-04019090.
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© 2019 American Society of Civil Engineers. The small strain shear modulus (Gmax) is an important parameter in geodynamic problems. To predict the Gmax of unsaturated soils that are normally subjected to complex drying and wetting processes, the effect of hydraulic hysteresis needs to be evaluated. Although several equations have been proposed in recent years, limitations still exist, requiring more research studies in this field. In this study, Gmax was investigated in a multistage test during several drying-wetting cycles and a loading-unloading cycle of net stress. The results revealed four key factors that directly influence the magnitude of Gmax: the void ratio, net stress, matric suction, and degree of saturation. Although variations of the void ratio, net stress, and matric suction cause persistent responses of Gmax (i.e., if all other factors remain unchanged, Gmax would then be reversely proportional to the void ratio and directly proportional to the net stress and matric suction), variations in the degree of saturation result in different responses. A decrease in the degree of saturation may induce a reduction or growth of Gmax because, on the one hand, it reduces the effect of matric suction, whereas on the other hand, it increases the total effect of van der Waals attractions and electric double-layer repulsions. At the same stress state, a reverse trend, induced by an increase in the degree of saturation, will occur with a growth in the effect of matric suction and a reduction in the combined effect of van der Waals attractions and electric double-layer repulsions. An analysis of the results showed that hydraulic hysteresis occurred in all the stress loops, and it directly influenced the response of Gmax. The effect of hydraulic hysteresis can only be captured if the van der Waals attractions and electric double-layer repulsions are considered. A model to estimate Gmax while incorporating the van der Waals attractions and electric double-la...
Nguyen, HH, Khabbaz, H & Fatahi, B 2019, 'A numerical comparison of installation sequences of plain concrete rigid inclusions', Computers and Geotechnics, vol. 105, pp. 1-26.
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© 2018 Elsevier Ltd Soil displacement induced when installing controlled modulus columns (CMC) as ground reinforcement could affect the columns installed close by. Realising numerical analyses may provide useful insights, this paper describes a numerical approach to investigate how groups of CMC installed in different sequences could affect columns installed previously. Coupled consolidation analyses in large strain mode and incorporating soil-CMC interaction were carried out using the three-dimensional finite difference software package FLAC3D. The CMCs were modelled using advanced non-linear Hoek-Brown material with a tensile yield criterion while soils with a typical profile were characterised using the modified Cam Clay and the elastic-perfectly plastic material with a Mohr-Coulomb yield criterion. Where possible, the predicted responses of ground surrounding the CMCs were compared to a number of existing analytical methods. Predictions revealed that lateral soil movement and soil heave near existing CMCs induced by installing new CMCs towards the existing CMCs were approximately 15% and 25% greater than corresponding predictions when a reverse installation sequence was adopted. The maximum excess pore water pressures, induced near existing columns due to installing new columns towards the existing ones, were almost twice more than those caused by the reverse sequence of installation. Moreover, the predicted bending moments generated in the existing columns induced by installing new columns towards the existing CMCs were almost 22% greater than the corresponding values when the reverse installation sequence was adopted. This shows the importance of selecting an appropriate installation sequence in the CMC construction process as well as considering the initial stress field and bending moments in the surrounding soil and CMCs, respectively when designing embankments on improved soft soils.
Nguyen, TN, Yu, Y, Li, J, Gowripalan, N & Sirivivatnanon, V 2019, 'Elastic modulus of ASR-affected concrete: An evaluation using Artificial Neural Network', Computers and Concrete, vol. 24, no. 6, pp. 541-553.
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Alkali-silica reaction (ASR) in concrete can induce degradation in its mechanical properties, leading to compromised serviceability and even loss in load capacity of concrete structures. Compared to other properties, ASR often affects the modulus of elasticity more significantly. Several empirical models have thus been established to estimate elastic modulus reduction based on the ASR expansion only for condition assessment and capacity evaluation of the distressed structures. However, it has been observed from experimental studies in the literature that for any given level of ASR expansion, there are significant variations on the measured modulus of elasticity. In fact, many other factors, such as cement content, reactive aggregate type, exposure condition, additional alkali and concrete strength, have been commonly known in contribution to changes of concrete elastic modulus due to ASR. In this study, an artificial intelligent model using artificial neural network (ANN) is proposed for the first time to provide an innovative approach for evaluation of the elastic modulus of ASR-affected concrete, which is able to take into account contribution of several influence factors. By intelligently fusing multiple information, the proposed ANN model can provide an accurate estimation of the modulus of elasticity, which shows a significant improvement from empirical based models used in current practice. The results also indicate that expansion due to ASR is not the only factor contributing to the stiffness change, and various factors have to be included during the evaluation.
Nimbalkar, Pain, Ahmad & Chen 2019, 'Stability Assessment of Earth Retaining Structures under Static and Seismic Conditions', Infrastructures, vol. 4, no. 2, pp. 15-15.
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An accurate estimation of static and seismic earth pressures is extremely important in geotechnical design. The conventional Coulomb’s approach and Mononobe-Okabe’s approach have been widely used in engineering practice. However, the latter approach provides the linear distribution of seismic earth pressure behind a retaining wall in an approximate way. Therefore, the pseudo-dynamic method can be used to compute the distribution of seismic active earth pressure in a more realistic manner. The effect of wall and soil inertia must be considered for the design of a retaining wall under seismic conditions. The method proposed considers the propagation of shear and primary waves through the backfill soil and the retaining wall due to seismic excitation. The crude estimate of finding the approximate seismic acceleration makes the pseudo-static approach often unreliable to adopt in the stability assessment of retaining walls. The predictions of the active earth pressure using Coulomb theory are not consistent with the laboratory results to the development of arching in the backfill soil. A new method is proposed to compute the active earth pressure acting on the backface of a rigid retaining wall undergoing horizontal translation. The predictions of the proposed method are verified against results of laboratory tests as well as the results from other methods proposed in the past.
Nimbalkar, SS, Punetha, P, Basack, S & Mirzababaei, M 2019, 'Piles Subjected to Torsional Cyclic Load: Numerical Analysis', Frontiers in Built Environment, vol. 5.
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Pile foundations supporting large structures (such as high-rise buildings, oil drilling platforms, bridges etc). are often subjected to eccentric lateral load (in addition to the vertical loads) due to the action of wind, waves, high speed traffic, and ship impacts etc. The eccentric lateral load, which is usually cyclic (repetitive) in nature, induces torsion in the pile foundation. This paper presents a numerical model based on boundary element approach to study the performance of a single pile subjected to the torsional cyclic load. The model is initially validated by comparing it with the experimental data available from the literature. Thereafter, the model has been utilized to conduct a parametric study to understand the influence of the torsional cyclic loading parameters on the axial pile capacity. The results indicated that the model is able to capture the degradation in the axial pile capacity due to the torsional cyclic loading with a reasonable accuracy. Moreover, the parametric study showed that the frequency, amplitude and number of cycles play a significant role in the torsional cyclic response of the pile. The present study is essential for the development of design guidelines for pile foundations subjected to torsional cyclic load.
Peng, Y, Wu, C, Li, J, Liu, J & Liang, X 2019, 'Mesoscale analysis on ultra-high performance steel fibre reinforced concrete slabs under contact explosions', Composite Structures, vol. 228, pp. 111322-111322.
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© 2019 Elsevier Ltd This paper develops a more efficient and applicable three-dimensional mesoscale model to simulate ultra-high performance steel fibre reinforced concrete (UHP-SFRC) slabs under contact explosions. In the proposed mesoscale model, UHP-SFRC consists of two components involving concrete matrix and steel fibres. The straight steel fibres are randomly distributed and orientated in the concrete matrix using the self-coding program. The proposed mesoscale model is firstly validated with a series of static and dynamic tests, and then it is adopted in the numerical simulation of contact explosions. With the verified mesoscale model, parametric studies are conducted to investigate the effects of slab thickness and TNT charge weight on the crater damage of UHP-SFRC slabs under contact explosions. Based on the results of parametric studies, a damage identification multi-classifier is constructed to recognize and predict the damage of UHP-SFRC slabs under contact explosions by using the support vector machine (SVM).
Rao, P, Zhao, L, Chen, Q & Nimbalkar, S 2019, 'Three-dimensional limit analysis of slopes reinforced with piles in soils exhibiting heterogeneity and anisotropy in cohesion', Soil Dynamics and Earthquake Engineering, vol. 121, pp. 194-199.
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© 2019 Elsevier Ltd Reinforcement of slopes by placing piles is one of the most common and effective techniques. Most of existing studies are limited to homogeneous and isotropic slopes, while in practice, the soil in the slope often exhibits heterogeneous and anisotropic characteristics. To address these issues, an innovative approach is introduced in this Technical Note to evaluate the stability of heterogeneous and anisotropic slopes incorporating the effect of anti-slide piles. Employing a three-dimensional upper-bound limit analysis, safety factor adopting the strength reduction technique is utilized herewith. The effects of soil heterogeneity and anisotropy with reference to cohesion on the optimal pile location and the slope stability in both cohesive-frictional and purely cohesive soils are investigated. The results amply demonstrate that the proposed limit analysis is appropriate for the stability assessment of reinforced slopes in heterogeneous and anisotropic soils. The safety factor increases with increase in heterogeneous factor and decrease in anisotropic factor. The optimal pile location is irrespective of these two factors, which should be carefully considered in engineering design.
Rao, P, Zhao, L, Chen, Q & Nimbalkar, S 2019, 'Three-Dimensional Slope Stability Analysis Incorporating Coupled Effects of Pile Reinforcement and Reservoir Drawdown', International Journal of Geomechanics, vol. 19, no. 4, pp. 06019002-06019002.
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© 2019 American Society of Civil Engineers. In pile-reinforced dams and bank slopes, the antislide effect of piles and drawdown of reservoirs are two aspects that could significantly affect the slope stability. However, existing studies have incorporated these two factors separately, albeit not in tandem. Moreover, stability assessment of these earth structures is usually performed ignoring the three-dimensional (3D) effect. To address these issues, the kinematic approach of limit analysis is adopted in this technical note for evaluating slope stability based on the 3D rotational failure mechanism. In addition, the coupled effects of pile reinforcement and water drawdown are considered. The analysis is performed for four types of drawdown cases. The results demonstrate that the optimal pile location undergoes significant change during the external drawdown process, while the effect of the declining water level on slope stability follows the similar pattern for varying pile locations.
Rasouli, H & Fatahi, B 2019, 'A novel cushioned piled raft foundation to protect buildings subjected to normal fault rupture', Computers and Geotechnics, vol. 106, pp. 228-248.
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© 2018 Elsevier Ltd Recent earthquake events have shown that besides the earthquake forces, interaction between the fault rupture and structure could cause a lot of damage to the surface and underground structures. Field observations have revealed a need to design structures for fault induced loading in regions with active faults. In this present study, three-dimensional numerical modelling using ABAQUS finite element software is used to study the interactive mechanism of normal fault rupture with a 20-story moment-resisting building frame sitting on a raft, connected piled raft, and cushioned piled raft foundations. The performance of a foundation-structure system is examined by considering geotechnical and structural performance objectives such as structural inter-story drift, raft displacement, and the bending moment and shear forces within the raft and piles. In order to improve the geotechnical and structural performance of foundations and buildings, a new foundation system with cushioned piles below the raft is proposed because of its superior performance with regards to raft rocking and permanent structural inter-story drifts under normal fault rupture. This proposed foundation system also curtailed the bending moments induced in the piles.
Samadi-Boroujeni, H, Altaee, A, Khabbaz, H & Zhou, J 2019, 'Application of buoyancy-power generator for compressed air energy storage using a fluid–air displacement system', Journal of Energy Storage, vol. 26, pp. 100926-100926.
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© 2019 Elsevier Ltd This study proposes a gravity power generator based on the fluid–air displacement system using Compressed Air Energy Storage from renewable energy sources to increase the solar and wind power system penetration in the power network. A computer model was applied to estimate the performance of the fluid–air displacement system, taking into account the effects of key design and operating parameters. Analysis of the system was performed to calculate the net energy generation as the difference between the energy input and the energy output. Simulation results indicated that the round-trip efficiency of the fluid–air displacement system was between 47% and 60%, assuming 80% compressor efficiency. Results also showed that a system generating the maximum energy density should have a speed of cylinders movement of 0.65 m/s, a cylinder-wall distance of 0.25 × diameter of the cylinder and a gap distance between centers of two tandem cylinders is equal to 1.25. Furthermore, a sensitivity analysis conducted on the main parameters of the system identified that the gap ratio and the buckets moving speed were the highly sensitive parameters to the design and operation of the proposed system. This study also demonstrates the feasibility of using the fluid-displacement system in energy storage from renewable energy technologies.
Shakor, P, Nejadi, S & Paul, G 2019, 'A Study into the Effect of Different Nozzles Shapes and Fibre-Reinforcement in 3D Printed Mortar', Materials, vol. 12, no. 10, pp. 1708-1708.
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Recently, 3D printing has become one of the most popular additive manufacturing technologies. This technology has been utilised to prototype trial and produced components for various applications, such as fashion, food, automotive, medical, and construction. In recent years, automation also has become increasingly prevalent in the construction field. Extrusion printing is the most successful method to print cementitious materials, but it still faces significant challenges, such as pumpability of materials, buildability, consistency in the materials, flowability, and workability. This paper investigates the properties of 3D printed fibre-reinforced cementitious mortar prisms and members in conjunction with automation to achieve the optimum mechanical strength of printed mortar and to obtain suitable flowability and consistent workability for the mixed cementitious mortar during the printing process. This study also considered the necessary trial tests, which are required to check the mechanical properties and behaviour of the proportions of the cementitious mix. Mechanical strength was measured and shown to increase when the samples were printed using fibre-reinforced mortar by means of a caulking gun, compared with the samples that were printed using the same mix delivered by a progressive cavity pump to a 6 degree-of-freedom robot. The flexural strength of the four-printed layer fibre-reinforced mortar was found to be 3.44 ± 0.11 MPa and 5.78 ± 0.02 MPa for the one-layer. Moreover, the mortar with different types of nozzles by means of caulking is printed and compared. Several experimental tests for the fresh state of the mortar were conducted and are discussed.
Shakor, P, Nejadi, S, Paul, G & Malek, S 2019, 'Review of Emerging Additive Manufacturing Technologies in 3D Printing of Cementitious Materials in the Construction Industry', Frontiers in Built Environment, vol. 4, pp. 1-17.
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Additive manufacturing is a fabrication technology that is rapidly revolutionizing the manufacturing and construction sectors. In this paper, a review of various prototyping technologies for printing cementitious materials and selected 3D printing techniques are presented in detail. Benchmark examples are provided to compare three well-known printing techniques; inkjet printing (binder jetting), selected laser sintering (SLS), and extrusion printing (extrusion based process). A comprehensive search in the literature was conducted to identify various mix designs that could be employed when printing cementitious materials. Aspects of concrete mix design are described, and some new experiments are conducted to analyse the printability of new mixes by the authors. Future research in the area of the rheology of cementitious materials and its relationship with the structural performance of finished concretes are highlighted.
Shakor, P, Nejadi, S, Paul, G, Sanjayan, J & Aslani, F 2019, 'Heat curing as a means of postprocessing influence on 3D printed mortar specimens in powderbased 3D printing', Indian Concrete Journal, vol. 93, no. 9, pp. 65-74.
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Inkjet (Powder-based) three-dimensional printing (3DP) shows significant promise in concrete construction applications. The accuracy, speed, and capacity to build complicated geometries are the most beneficial features of inkjet 3DP. Therefore, inkjet 3DP needs to be carefully studied and evaluated with construction goals in mind and employed in real-world applications, where it is most appropriate. This paper focuses on the important aspect of curing 3DP specimens. It discusses the enhanced mechanical properties of the mortar that are unlocked through a heat-curing process. Experiments were conducted on cubic mortar specimens that were printed and cured in an oven at a range of different temperatures (40, 60, 80, 90, 100°C). The results of the experimental tests showed that 80°C is the optimum heat-curing temperature to achieve the highest compressive strength and flexural strength of the printed mortar specimens. These tests were performed on two different dimensions of the cubic specimens, namely, 20x20x20 mm, 50x50x50 mm and on prism specimens with dimensions of 160x40x40 mm. The inkjet 3DP process and the post-processing curing are discussed. In addition, 3D scanning of the printed specimens was employed and the surface roughness profiles of the 3DP gypsum specimens and cement mortar are recorded 13.76 µm and 22.31 µm, respectively.
Shakor, P, Nejadi, S, Paul, G, Sanjayan, J & Nazari, A 2019, 'Mechanical Properties of Cement-Based Materials and Effect of Elevated Temperature on 3-D Printed Mortar Specimens in Inkjet 3-D Printing', ACI Materials Journal, vol. 116, no. 2, pp. 55-67.
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Copyright © 2019, American Concrete Institute. All rights reserved. Three-dimensional (3-D) printers have the potential to print samples that can be used as a scaffold for a variety of applications in different industries. In this paper, cement-based materials including ordinary portland cement, calcium aluminate cement (passing 150 µm [0.0059 in.] size sieve), and fine sand were investigated as the cement-based materials in inkjet 3-D printing. Prism specimens were printed for the three-point bending test; and cubic specimens were printed for the uniaxial compressive strength test. Prism samples were printed along different directional axes (X, Y, and Z). The tests were conducted at different saturation levels (water-cement ratio [w/c]) as represented by S100C200, S125C250, S150C300, and S170C340. The prism specimens were cured in water for 7 and 28 days while cubic specimens were cured in Ca(OH) 2 and water for 7 and 28 days at the same ambient temperatures. In general, the results changed according to the directional axes of the prisms. However, following water curing, the cubic samples were heated up to 40°C (104°F) in an oven and a higher compressive strength was evident compared to the samples which were only cured in the room-temperature water. The wettability test for both powders has been conducted in the presented study.
Shao, R, Wu, C, Su, Y, Liu, Z, Liu, J & Xu, S 2019, 'Numerical analysis on impact response of ultra-high strength concrete protected with composite materials against steel ogive-nosed projectile penetration', Composite Structures, vol. 220, pp. 861-874.
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© 2019 Elsevier Ltd In order to investigate the impact behaviours of ultra-high strength concrete (UHSC) target protected with high-toughness lightweight energy absorption composite materials against the projectile penetration thoroughly, a numerical study using LS-DYNA is conducted at impact velocities between 540 m/s and 810 m/s. The major compositions of FE models are the same as those of experimental specimens which include steel wire mesh reinforced concrete (SWMRC) plates, UHMWPE fibre laminates, aluminium foam sheets and the protected UHSC. Numerical results involving depth of penetration (DOP), impact crater (exfoliated) diameter of SWMRC plates, localized damage and ballistic deviation of the projectiles are obtained and then compared with experimental data, where the numerical results show reasonable agreement with the test results. Based on the validated FE models, the projectile penetration process and the energy evolution between the target and the projectile are studied. In addition, a parametric analysis is conducted to investigate the influence of the arrangement order for present composite materials on DOP and impact resistance of reinforced UHSC target, as well as the ballistic deviation and deformation of the projectile. Results of this study indicate that for the current UHSC target, firstly, the ballistic deviation and projectile deformation are two important factors affecting the impact resistance of the target; secondly, the fibre laminates play a major role in the projectile ballistic deviation and the impact kinetic energy of the projectile is mainly absorbed by the concrete matrix, multilayer steel wire meshes and different densities of foam sheets.
Shao, R, Wu, C, Su, Y, Liu, Z, Liu, J, Chen, G & Xu, S 2019, 'Experimental and numerical investigations of penetration resistance of ultra-high strength concrete protected with ceramic balls subjected to projectile impact', Ceramics International, vol. 45, no. 6, pp. 7961-7975.
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© 2019 Elsevier Ltd and Techna Group S.r.l. Ceramic materials characterized by high hardness, high inherent strength, low density and excellent dimensional stability have been extensively applied in the design of high-performance and lightweight protective structures to resist the high-speed projectile impact. In order to study the anti-penetration capability of ceramic balls protected ultra-high strength concrete (CB-UHSC), high-speed projectile impact tests were conducted at striking velocities of 545 m/s, 679 m/s, and 809 m/s to investigate the impact performance of ceramic balls, projectiles, and the protected UHSC. The experimental results indicated the effectiveness and economy of ceramic balls in resisting the high-speed projectile impact. Numerical studies were then conducted to reproduce the projectile penetration process within CB-UHSC targets with the assistance of LS-DYNA. Based on the validated numerical models, impact resistance and ballistic deviation of projectiles, as well as the energy evolution between projectiles and targets, were further investigated to comprehensively understand the impact performance of this newly designed protective structure under projectile penetration.
Singh, AM & Ha, QP 2019, 'Fast Terminal Sliding Control Application for Second-order Underactuated Systems', International Journal of Control, Automation and Systems, vol. 17, no. 8, pp. 1884-1898.
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© 2019, ICROS, KIEE and Springer. In this paper, we propose a robust and finite-time control method, based on the terminal sliding mode (TSM), for a class of two-degree-of-freedom (2-DOF) underactuated electromechanical systems subject to bounded uncertainties and disturbances. First, the proposed Fast Terminal Sliding Mode (FTSM) method is presented. Then for the underactuated system control, hierarchical sliding surfaces are defined, consisting of two layers. In the first layer, separate FTSM sliding functions are selected for each state of the system. In the second layer, the system sliding manifold is a linear combination of the first layer sliding surfaces. A control law is derived and stability conditions of the nonlinear system are obtained by using the Lyapunov theory. To verify the effectiveness of our proposed method, the developed control technique is applied to control both the swinging load and the cart position of an underactuated gantry crane. Extensive simulation and real-time experiments demonstrate enhanced performance of the system and robustness against parametric variations in comparison to conventional TSM and sliding mode control.
Sirivivatnanon, V 2019, 'Sixty-Year Service Life of Port Kembla Saltwater Concrete Swimming Pool', ACI Materials Journal, vol. 116, no. 5, pp. 31-36.
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© 2019 American Concrete Institute. All rights reserved. The durability performance of Port Kembla Olympic Pool, built in 1937, has been investigated. Nearly all structural components were reinforced concrete and were exposed to marine environments with some components ‘permanently submerged’ while others were in an ‘atmospheric zone’ and ‘tidal or splash zone.’ After more than 60 years in service, most structural components were found to be in excellent condition. This paper discusses the site investigation that examined strength, carbonation, chloride penetration, and cover depths. The results revealed the quality of the concrete to be uniform in the pool but variable in other structural members. There was little carbonation but extensive chloride penetration, depending on the exposure condition. The average compressive strength of the 60-year-old concrete in the pool and its surrounding structures was 5700 and 4280 psi (40 and 30 MPa), respectively. The covers were between 2.0 and 2.5 in. (50 and 65 mm). Despite the extent of chloride penetration into the cover concrete, limited corrosion was observed. The concrete has proven to give a service life of over 60 years, which confirms the importance of achieving adequate strength and, perhaps more importantly, cover.
Stuart, BH, Maynard-Casely, HE, Booth, N, Leung, AE & Thomas, PS 2019, 'Neutron diffraction of deuterated tripalmitin and the influence of shear on its crystallisation', Chemistry and Physics of Lipids, vol. 221, pp. 108-113.
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© 2019 This neutron diffraction study of deuterated tripalmitin has provided further insight into a forensic observation of the crystallisation of lipids under high-shear conditions. To achieve this, an experimental set up was designed to enable simultaneous rheological data from a Couette cell to be recorded with neutron powder diffraction, enabling the influence of shear on the polymorph transformation on cooling to be monitored in real time. Tripalmitin was observed to directly transform from a liquid phase to a β polymorph under the influence of shear. Although the liquid to β transition was not observed to be influenced by shear rate, the degree of crystallinity, qualitatively denoted by an increase in the sharpness of the diffraction peaks, was observed at higher shear rates. Evidence is also presented that the rate of cooling influences the ordering in the β-polymorph produced in zero shear conditions.
Stuart, BH, Thomas, PS, Barrett, M & Head, K 2019, 'Modelling clay materials used in artworks: an infrared spectroscopic investigation', Heritage Science, vol. 7, no. 1.
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Abstract Modelling clays are utilised by artists for their malleable properties. One of the challenges in managing collections containing such materials is the variety of commercial compositions available and, therefore, the variation in the requirements for storage and maintenance of such artefacts. The Art Gallery of New South Wales in Australia is responsible for the care of a range of artworks that contain modelling materials, some of which show detrimental property changes and there is concern for the longevity of such works. The aim of the current research is to determine the compositions of the modelling materials utilised in works produced by different artists in the gallery’s collection. Infrared spectroscopy was used to identify the main constituents of samples collected from the works of four different artists and a variety of material types were determined. Oil-based, air-hardening and polymer clays of varying composition were identified in the survey of artworks. Signs of deterioration in particular artworks were able to be characterised using spectroscopy, with the mechanisms identified including loss and oxidation of the oil component. Where a polymer clay was chosen by one artist, the distortion of the artwork was due to flow of the material over time and demonstrates the need for an understanding of the long term properties of the materials being used. The study has highlighted the need for conservators to have a detailed understanding of modelling materials to ensure the longevity of artworks containing this class of materials.
Sullivan, C, Thomas, P & Stuart, B 2019, 'An atomic force microscopy investigation of plastic wrapping materials of forensic relevance buried in soil environments', Australian Journal of Forensic Sciences, vol. 51, no. 5, pp. 596-605.
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© 2018 Australian Academy of Forensic Sciences Plastics are one means of disposal of items or remains associated with criminal activity. The surface characteristics of plastic wrapping materials of forensic interest in soil environments have been investigated to determine the environmental factors that have the greatest influence on the degradation process of such polymers. Polyethylene bags and poly(vinyl chloride) sheeting were buried in model environments encompassing different soil types, moisture content, pH and temperature. Atomic force microscopy was used to monitor the changes to the polymer surface at a nanometre level. Over a two-year burial period, the degradation of polyethylene was found to be enhanced by an increased moisture content and an elevated soil pH. The plasticizer content of poly(vinyl chloride) was affected by burial and was observed to leach from the plastic in all environments continually over the burial period. A moist environment was shown to have a more pronounced effect on the removal of plasticizer. A measurement of the surface roughness of plastics using atomic force microscopy has been shown to be sensitive to the burial environment and demonstrates the potential of this technique to measure relatively subtle changes to burial items exposed to different environments.
Sun, Y & Nimbalkar, S 2019, 'Stress-fractional soil model with reduced elastic region', Soils and Foundations, vol. 59, no. 6, pp. 2007-2023.
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Sun, Y, Nimbalkar, S & Chen, C 2019, 'Particle breakage of granular materials during sample preparation', Journal of Rock Mechanics and Geotechnical Engineering, vol. 11, no. 2, pp. 417-422.
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© 2019 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences Particle breakage is commonly observed in granular materials when subjected to external loads. It was found that particle breakage would occur during both sample preparation and loading stages. However, main attention was usually paid to the particle breakage behaviour of samples during loading stage. This study attempts to explore the breakage behaviour of granular materials during sample preparation. Triaxial samples of rockfill aggregates are prepared by layered compaction method to achieve different relative densities. Extents of particle breakage based on the gradings before and after test are presented and analysed. It is found that particle breakage during sample preparation cannot be ignored. Gradings after test are observed to shift away from the initial grading. Aggregates with larger size that appear to break are more than the smaller-sized ones. Irrespective of the initial gradings, an increase in the extent of particle breakage with the increasing relative density is observed during sample preparation.
Tan, X, Li, W, Zhao, M & Tam, VWY 2019, 'Numerical Discrete-Element Method Investigation on Failure Process of Recycled Aggregate Concrete', Journal of Materials in Civil Engineering, vol. 31, no. 1, pp. 04018353-04018353.
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© 2018 American Society of Civil Engineers. This study numerically investigates the failure processes of recycled aggregate concrete (RAC) and natural aggregate concrete (NAC). A two-dimensional simulation based on a discrete-element method (DEM) is conducted with a universal distinct-element code (UDEC) program. RAC is modeled by a combination of rigid Voronoi blocks cemented to each other using contacts for interfaces. The determination procedure of contact microparameters is analyzed, and a series of microscopic contact parameters in different components of modeled recycled aggregate concrete (MRAC) is calibrated using nanoindentation results. The complete stress-strain curves, fracture process, and failure pattern of numerical model are verified by experimental results, proving its accuracy and validation. The initiation, propagation, and coalescence of microcracks and subsequent nonlinear deformation behaviors of cement mortar, modeled natural aggregate, and recycled aggregate concrete are captured through DEM numerical simulations and compared with digital image correlation (DIC) results. It is found that both the new interfacial transition zone and the old interfacial transition zone are the weak links in RAC, where most microcracks initiate and propagate into the cement mortar region. The failure behaviors of MRAC revealed by both experimental and numerical results can effectively provide insights into the failure mechanism and enhancement of RAC.
Tang, Z, Li, W, Hu, Y, Zhou, JL & Tam, VWY 2019, 'Review on designs and properties of multifunctional alkali-activated materials (AAMs)', Construction and Building Materials, vol. 200, pp. 474-489.
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© 2018 Elsevier Ltd The stream of research on alkali-activated materials (AAMs) has expanded rapidly during the last decades owing to the potential as a viable alternative to cement-based materials. In addition to the load-carrying function, AAMs have been integrated with other functions to develop advanced construction materials, namely multifunctional AAMs. Multifunctional AAMs are intelligent systems not only serve a basic structural function but also exhibit other functional properties or have the abilities to react upon external stimuli or disturbances. Materials of this kind have tremendous potential to enhance the mechanical performance and durability of structure, improve the reliability and longevity of infrastructure, as well as reduce life-cycle service and maintenance cost. These multifunctional properties are mainly achieved through materials composition design, incorporation of functional elements, or microstructure modification. This paper presents an overview on designs and properties of multifunctional AAMs covering the smart functions, mechanical functions, and electrical functions, and with special attention to their definition, principles, and current progress. Furthermore, the challenges in the research of multifunctional AAMs have been discussed, as well as the future directions to increase the innovation and engineering application of these materials and structures.
Tang, Z, Li, W, Ke, G, Zhou, JL & Tam, VWY 2019, 'Sulfate attack resistance of sustainable concrete incorporating various industrial solid wastes', Journal of Cleaner Production, vol. 218, pp. 810-822.
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© 2019 Elsevier Ltd Industrial solid wastes are inducing severe environmental problems, but the problem can be overcame by reusing them as construction materials. The sulfate resistances of sustainable concrete incorporating various solid waste materials, including waste glass powder (WGP), coal gangue powder (CGP) and fly ash (FA) were investigated in this study. Concrete mixes with different water to binder (w/b) ratios and containing various solid waste materials as partial replacement of Portland cement by ratios of 10%, 20%, and 30% were prepared. These mixes were immersed in the 5% Na 2 SO 4 solution for a total period of 22 months. The sulfate attack resistances were evaluated extensively based on visual appearance, mass change, compressive strength, splitting tensile strength, ultrasonic pulse velocity, mineralogy, and microstructure. The results indicate that regardless of the type and content of solid waste materials, the replacement of cement by solid waste materials exhibit a positive impact on the sulfate attack resistance. Under the same substitution level, WGP appear to be the most effective in offsetting the destructive effect of sulfate attack, followed by CGP and FA. Therefore, sustainable concrete incorporating solid waste materials can not only promote the recycling of solid waste, but also provide high sulfate attack resistance.
Tang, Z, Shan, B, Li, WG, Peng, Q & Xiao, Y 2019, 'Structural behavior of glubam I-joists', Construction and Building Materials, vol. 224, pp. 292-305.
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© 2019 Elsevier Ltd Glubam, a new type of engineered bamboo composites, is a promising structural material characterized by outstanding mechanical performance and environmental friendliness. In this study, glubam I-joists, with the spans ranging from 2.4 m to 7.5 m, were prepared and tested to evaluate their structural behavior. The glubam I-joists were lengthened by finger joints, and two kinds of connections were used to connect the web and flanges. Four-point bending tests were conducted to examine the failure modes, load-deflection relationships and load carrying capacity of glubam I-joists. Test results indicated that the dominant failure modes of glubam I-joists included shear failure at the finger joint in the web, bending failure at the finger joint in the bottom flange and lateral buckling. Correspondingly, the load carrying capacity of glubam I-joists was governed by the bending strength, shear capacity and critical bending moment. Glubam I-joists have relatively higher mechanical performance compared with other engineered bamboo or timber I-joists with similar dimension, and the bending capacity of the glubam I-joist with continuous web-to-flange connection meets the requirement specified in Chinese code. Based on the experimental findings and existing methods, theoretical methods were proposed for predicting the stiffness and load carrying capacity of glubam I-joist and were also validated by the test results.
Tao, M, Li, Z, Cao, W, Li, X & Wu, C 2019, 'Stress redistribution of dynamic loading incident with arbitrary waveform through a circular cavity', International Journal for Numerical and Analytical Methods in Geomechanics, vol. 43, no. 6, pp. 1279-1299.
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SummaryIn actual geotechnical and civil engineering, dynamic stress concentrations around cavities generated by wave sources widely exist. In this study, based on the complex variable theory and Fourier transform method, the expression of the dynamic stress concentration factor (DSCF) around a circular cavity in infinite homogeneous media subjected to transient waves with arbitrary waveform is obtained. The relationships between both steady‐state and transient DSCF and their waveform parameters are investigated quantitatively. The results indicate that a relatively large tensile stress is generated with low Poisson's ratio under steady‐state incidence. Under the condition of transient incidence, the position of the wave peak has a minor effect on the DSCF in the case of small wavenumber, but it has a significant effect in the opposite case. It is found that when the wavenumber is high, such as 0.5, the stress response lags behind the stress wave. In addition, the closer the wave peak to the center of the waveform, the greater the potential damage of the transient incidence.
Thanh, HT, Li, J & Zhang, YX 2019, 'Numerical modelling of the flow of self-consolidating engineered cementitious composites using smoothed particle hydrodynamics', Construction and Building Materials, vol. 211, pp. 109-119.
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Thomas, P, Aldrige, L & Smallwood, A 2019, 'Water in opal – what can it tell us?', InColor Magazine, no. 41, pp. 62-69.
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Opal is a hydrous silica composed of predominantly silicon dioxide and water. The chemical composition of opal is normally described by the general formula SiO2.nH2O. The formula indicates that opal contains water and the value of ‘n’ is variable so the water content is variable and is known to range widely. Such a simple formula hides much of the important characteristics of how water is contained in opal and the variability in the water content and states of water is intricately involved in the formation of opal and may influence properties of the opal as a gemstone. The understanding of the states of water in opal is therefore of importance. The way in which the water is contained provides clues to the mechanisms of formation of opal. The water contained may also be used as a probe to help elucidate the complex microstructure beyond the sphere array structure in which precious opal, in particular, is described. This article will outline the types of water present in opal that displays play-of colour (POC) and how these types have been determined using chemical and physical laboratory characterisation techniques.
Tian, Z, Li, Y, Zheng, J & Wang, S 2019, 'A state-of-the-art on self-sensing concrete: Materials, fabrication and properties', Composites Part B: Engineering, vol. 177, pp. 107437-107437.
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© 2019 Elsevier Ltd Self-sensing concrete combines electrically conductive filler material and conventional building material together, and is able to realise a sensing function that by measuring the change of electrical properties of the composite under external loading, the stress, deformation and damage could be monitored. It has the advantages of high sensitivity, long service period, excellent compatibility, durability and mechanical strength, and low maintenance cost, and can be potentially applied in structure health monitoring, weight in motion, traffic detection, parking management and many other fields. This paper overviews the details of the composition and role of each component, the fabrication method and the mechanism of the self-sensing concrete. The future prospects are discussed at the end of the paper.
Tuan, LA, Ha, Q & Van Trieu, P 2019, 'Observer-Based Nonlinear Robust Control of Floating Container Cranes Subject to Output Hysteresis', Journal of Dynamic Systems, Measurement, and Control, vol. 141, no. 11, pp. 111002-111002.
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A container crane mounted on a pontoon is utilized to transfer containers to smaller ships when a large container ship cannot reach the shallow water port. The shipboard container is considered as an underactuated system having complicated kinematic constraints and hysteretic nonlinearities, with only two actuators to conduct simultaneous tasks: tracking the trolley to destination, lifting the container to the desired cable length, and suppressing the axial container oscillations and container swing. Parameter variations, wave-induced motions of the ship, wind disturbance, and nonlinearities remain challenges for control of floating container cranes. To deal with these problems, this study presents the design of two nonlinear robust controllers, taking into account the influence of the output hysteresis, and using velocity feedback from a state observer. Control performance of the proposed controllers is verified in both simulation and experiments. Together with consistently stabilizing outputs, the proposed control approach well rejects hysteresis and disturbance.
Vahedian, A, Shrestha, R & Crews, K 2019, 'Experimental and analytical investigation on CFRP strengthened glulam laminated timber beams: Full-scale experiments', Composites Part B: Engineering, vol. 164, pp. 377-389.
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Vakhshouri, B & Nejadi, S 2019, 'Empirical models and design codes in prediction of modulus of elasticity of concrete', Frontiers of Structural and Civil Engineering, vol. 13, no. 1, pp. 38-48.
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© 2018, Higher Education Press and Springer-Verlag GmbH Germany, part of Springer Nature. Modulus of Elasticity (MOE) is a key parameter in reinforced concrete design. It represents the stress-strain relationship in the elastic range and is used in the prediction of concrete structures. Out of range estimation of MOE in the existing codes of practice strongly affect the design and performance of the concrete structures. This study includes: (a) evaluation and comparison of the existing analytical models to estimating the MOE in normal strength concrete, and (b) proposing and verifying a new model. In addition, a wide range of experimental databases and empirical models to estimate the MOE from compressive strength and density of concrete are evaluated to verification of the proposed model. The results show underestimation of MOE of conventional concrete in majority of the existing models. Also, considering the consistency between density and mechanical properties of concrete, the predicted MOE in the models including density effect, are more compatible with the experimental results.
Vakhshouri, B, Rasiah, SR & Nejadi, S 2019, 'Analytical study of the drying shrinkage in light-weight concrete containing EPS beads', Advances in Cement Research, vol. 31, no. 7, pp. 308-318.
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This study investigates the drying shrinkage of light-weight concrete containing expanded polystyrene beads. Nine shrinkage specimens in three groups were subjected to three different conditions of drying and wetting periods for 450 d. The effect of the weight loss of specimens on the shrinkage is studied. A proposed new relationship to predict the shrinkage behaviour of the specimens is verified by the existing models. A bilinear relationship between the rate of weight loss and shrinkage increment is also developed. Results show that a longer curing period strongly affects the shrinkage behaviour over the first few months. The rate of weight loss, rate of shrinkage with time and the ratio of the rate of weight loss to the initial weight of specimens are also investigated.
Vinod, M & Khabbaz, H 2019, 'Comparison of rectangular and circular bored twin tunnels in weak ground', Underground Space, vol. 4, no. 4, pp. 328-339.
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© 2019 Tongji University and Tongji University Press The recent innovation of a rectangular tunnel boring machine (TBM), and its use in the Hongzhuan Road tunnel underpass by the China Railway Engineering Group (CREG), has revitalized shallow depth soft soil tunneling. This paper presents the findings of a numerical study using PLAXIS to determine the surface settlements and moments produced in tunnel linings for circular and rectangular twin tunnels. The effects of the relative positions of twin tunnels, critical distances, volume losses, depths of burial, and tunnel sizes for both circular and rectangular tunnels are the key parameters of this investigation. The results indicate that rectangular tunnels are suitable for shallow depths in weak ground as they have lesser settlement compared with circular tunnels. This is crucial for tunneling beneath important structures such as railway lines and existing roads. However, the maximum bending moment produced in the rectangular tunnel lining is higher than that for circular tunnels. The use of rectangular TBMs is an unconventional method in modern day tunneling; however, the analysis in this project recommends that tunnel industry engineers consider this method for shallow depth weak ground tunneling.
Vu, T, Gowripalan, N, De Silva, P, Kidd, P & Sirivivatnanon, V 2019, 'Influence of curing and retarder on early-age properties of powder geopolymer concrete', Concrete in Australia, vol. 45, no. 2, pp. 41-46.
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Dry powder geopolymer is a new approach to geopolymer production for field applications. However, this new production technique has a limitation of rapid setting time. Until now, most studies on retarders for geopolymers were performed for a two-part mix. This paper aims to determine the influence of a sodium based retarder on setting time of dry powder geopolymer from a blend of fly ash and slag. With 2% of retarder, initial setting time of dry powder geopolymer (fly ash 50%, slag 32%) was 80-110 minutes. For dry powder geopolymer using 4% retarder (fly ash 30%, slag 50%) initial setting time was 53-75 minutes. Considering heat evolution, workability and compressive strength, the optimum retarder dosage was about 2 - 4% (by weight of dry powder). For precast elements, sealed and heat curing was found to be an effective curing regimeThe effect of different curing conditions and the addition of a retarder on flow characteristics, setting time and strength development of a powder form of geopolymer is reported.
Wang, D, Wu, C, Huang, W & Zhang, Y 2019, 'Vibration investigation on fluid-structure interaction of AP1000 shield building subjected to multi earthquake excitations', Annals of Nuclear Energy, vol. 126, pp. 312-329.
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© 2018 Elsevier Ltd Fluid-structure interaction (FSI) between water and water tank of AP1000 nuclear power plant has always been a hot topic because the gravity water tank plays a key role in protecting structural safety in an emergency such as an earthquake. The main target of this study is to investigate the FSI effect on structural dynamic responses of AP1000 shield building with filled and empty water tanks and to explore the most reasonable height of water level for reducing seismic response under inputs of multi three-direction earthquake excitations. For this purpose, method of nonlinear FSI algorithm of finite element is employed based on ANSYS platform. The numerical procedure is validated by comparison with theoretical calculation and existing experimental results of fluid free vibration and structural seismic responses in the situation of El Centro wave. Based on the validated numerical model, a series of numerical simulations on seven partially-filled models in six natural and one artificial earthquake are carried out and corresponding results, such as peak acceleration & displacement, floor response spectrum and structural base shear, are studied comparatively in details. Discussions of this study show that the partially-filled shield building appears significant FSI effect, which generates great influence on structural dynamic characteristics and responses. Reasonable design of the water level can contribute to reducing structural responses and improving seismic safety.
Wang, D, Wu, C, Zhang, Y & Li, S 2019, 'Study on vertical vibration control of long-span steel footbridge with tuned mass dampers under pedestrian excitation', Journal of Constructional Steel Research, vol. 154, pp. 84-98.
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© 2018 Elsevier Ltd This paper aims to study crowd-induced vibration control of long-span steel footbridges with different dynamic characteristics by combining methods of site measurement and numerical simulation. Four kinds of footbridge models with sensitive vertical natural frequencies of easily generating human-bridge resonance under pedestrian loading are designed based on an actual steel footbridge. The numerical models are firstly validated by comparative investigation between the site measurement and the simulation. Detailed study on dynamic responses of the four footbridges with and without controlling systems of tuned mass damper (TMD) and multiple tuned mass damper (MTMD) is then conducted under 13 cases of crowd random excitations, rhythmic running and jumping excitations. Results show that the numerical simulation agrees well with the site measurement data. TMD system is found to be highly efficient in reducing vibration responses only when the excitation frequency is basically consistent with the structural natural frequency, which obviously limits the application of TMD system in footbridges as wider excitation frequency bandwidth is caused by human activities. MTMD system are demonstrated to be with higher vibration absorption robustness appearing predominant and stable capacity of reducing structural vibrations under all the crowd random and rhythmic excitations for the four footbridges.
Wang, D, Wu, C, Zhang, Y, Ding, Z & Chen, W 2019, 'Elastic-plastic behavior of AP1000 nuclear island structure under mainshock-aftershock sequences', Annals of Nuclear Energy, vol. 123, pp. 1-17.
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© 2018 Elsevier Ltd This paper studies dynamic responses of AP1000 nuclear island structure in strong earthquake sequences. A numerical model to simulate nuclear structural behaviors in earthquake is validated by comparison with data from a previous study on a nonlinear dynamic analysis of a reinforced concrete shield building. The validated numerical model is then used to carry out a series of parametric analyses with 112 computational cases so as to determine influence of strong aftershocks on structural elastic-plastic behavior considering input of three-dimensional ground motions. The results indicate that the influence of aftershocks on structural horizontal/vertical dynamic responses is very small in design basis earthquake sequences. However, the influence must be considered seriously in beyond-design basis earthquake sequences as values of RMVs (Ratio of Mean Value) deviating IPRs (Input Peak Ratio) obviously, which means structural dynamic responses are greatly changed in strong aftershocks. Damage aggravating effect induced by strong aftershocks can cause severe damage of structural members and it is found the greater the magnitude of aftershocks, the severer the aggravation effect. Although earthquake input energy is mostly dissipated by damping energy, plastic damage energy plays considerable role in strong aftershocks as it shares beyond 8 percent of the total input energy, which is 10 times more compared to design basis earthquake sequences.
Wang, D, Zhang, Y, Wu, C, Xue, G & Huang, W 2019, 'Seismic performance of base-isolated AP1000 shield building with consideration of fluid-structure interaction', Nuclear Engineering and Design, vol. 353, pp. 110241-110241.
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© 2019 Elsevier B.V. Seismically-induced FSI effect on dynamic responses of AP1000 shield building with base isolation is focused in this study using numerical simualtion. The numerical model is firstly validated by comparison with existing experimental results, which is capable of simulating dynamic behaviors of the water partially-filled shield building with seismic isolation using high damping rubber (HDR) bearings. The influences of FSI on seismic performance of the base-isolated and base-fixed AP1000 shield building with various water levels and on the corresponding isolation effectiveness are comparatively explored in details. Results show that base isolation can reduce the fundamental frequency of the shield building and make it close to water sloshing frequency. It is necessary to ensure an reasonable isolation design to keep the fundamental frequency away from the sloshing frequency and then to avoid the water resonance. Seismic isolation can offer a substantial benefit for the earthquake-resistant design of the shield building even filled with different levels of water, because the structural primary resonance is effectively transformed to the sub-resonance by application of base isolation. Dynamic responses of base-isolated models are influenced significantly by FSI and an optimal water level ratio of 0.8 is suggested to achieve excellent seismic performance for such structures.
Wang, H, Li, Y, Zhang, G & Wang, J 2019, 'Effect of temperature on rheological properties of lithium-based magnetorheological grease', Smart Materials and Structures, vol. 28, no. 3, pp. 035002-035002.
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© 2019 IOP Publishing Ltd. This paper investigates the impact of temperature on the rheological properties of magnetorheological (MR) grease containing carbonyl iron suspended in lithium-based grease Lithium-based MR grease with 70% weight fraction of carbonyl iron is firstly prepared by mechanical mixing. The apparent viscosity and shear stress as a function of shear rate under different temperatures and magnetic field strengths are measured and discussed. It is found that the influence of temperature on apparent viscosity reduces with the increase of magnetic field strength. The dynamic properties of MR grease are obtained under oscillatory shear test. The influences of strain amplitude, driving frequency and magnetic field on the dynamic properties of MR grease at different temperature are discussed. The results demonstrate that the enhancement of temperature leads to the increase of storage modulus and the reduction of the loss factor. Microstructural variation of grease matrix at different temperature is proposed as an explanation of the rheological changes of MR grease.
Wang, W, Wu, C & Liu, Z 2019, 'Compressive behavior of hybrid double-skin tubular columns with ultra-high performance fiber-reinforced concrete (UHPFRC)', Engineering Structures, vol. 180, pp. 419-441.
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© 2018 Elsevier Ltd This study presents the results of an experimental program on the compressive behavior of hybrid fiber-reinforced polymer (FRP)-concrete-steel double-skin tubular columns (DSTCs) with ultra-high performance fiber-reinforced concrete (UHPFRC). In total 40 specimens, including 32 hybrid DSTCs and eight FRP confined solid concrete (FCSC) specimens, were prepared and tested under axial compression. In addition to hybrid UHPFRC DSTCs, hybrid DSTCs with ultra-high performance concrete without steel fiber addition (UHPC), high-strength concrete (HSC), and normal-strength concrete (NSC) were also tested. The investigated parameters included the FRP tube thickness, steel tube thickness, void ratio, steel fiber addition, concrete type, UHPFRC-filling inside the steel tube, and the column type. The test results indicate that the hybrid UHPFRC DSTCs can exhibit highly ductile behavior when a thick FRP tube is used. However, due to the ultra-high strength and the dense microstructure of UHPFRC, the hybrid UHPFRC DSTCs are likely to exhibit more brittle behavior than the hybrid DSTCs with NSC and HSC. Even though a high confinement level is provided, sudden stress reduction or stress fluctuations can be observed for the UHPFRC in hybrid DSTCs. The influences of FRP tube thickness, void ratio, steel fiber addition, and UHPFRC-filling inside the steel tube on the compressive behavior of the hybrid UHPFRC DSTCs are significant, while the influence of steel tube thickness is insignificant. Moreover, when compared to the FCSC specimens, the presence of an inner void is beneficial for the compressive behavior of UHPFRC in the hybrid DSTCs, especially when a thick FRP tube is used. Furthermore, the performance of existing stress-strain model to predict the compressive behavior of UHPFRC in the hybrid DSTCs is investigated.
Wang, W, Wu, C, Li, J, Liu, Z & Lv, Y 2019, 'Behavior of ultra-high performance fiber-reinforced concrete (UHPFRC) filled steel tubular members under lateral impact loading', International Journal of Impact Engineering, vol. 132, pp. 103314-103314.
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© 2019 This study investigates the behavior of ultra-high performance fiber-reinforced concrete (UHPFRC) filled steel tubular (UHPFRCFST) members under lateral impact loading. A total of five specimens were prepared and tested under lateral impact loading. All specimens were 168 mm in diameter and 2000 mm in length. In addition to UHPFRCFST members, normal strength concrete (NSC) filled steel tubular (NSCFST) members were also tested for comparison purpose. Other investigated parameters in this study include the impact energy and the presence of an inner void. The test results show that as compared to the NSCFST members, the UHPFRCFST members exhibit higher lateral impact resistance with higher peak and plateau impact forces, smaller deflection, and less local indentation. With the increase of impact energy, the peak impact force, the impact duration, and the deflection of the UHPFRCFST members are increased, while the plateau impact force is almost kept constant. Moreover, the presence of an inner void does not deteriorate the lateral impact resistance of the UHPFRCFST members. Finite element (FE) model was then developed and validated by the test results in this study. Afterwards, full-range analysis was performed to investigate the damage evolution, sectional bending moment distribution, and the interactions between the steel tube and the concrete during the impact process. Finally, detailed parametric analyses were carried out to investigate the influences of different parameters on the lateral impact behavior of UHPFRCFST members.
Wang, W, Wu, C, Li, J, Liu, Z & Zhi, X 2019, 'Lateral impact behavior of double-skin steel tubular (DST) members with ultra-high performance fiber-reinforced concrete (UHPFRC)', Thin-Walled Structures, vol. 144, pp. 106351-106351.
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© 2019 Elsevier Ltd This study investigates the lateral impact behavior of double-skin steel tubular (DST) members with ultra-high performance fiber-reinforced concrete (UHPFRC). A total of six specimens were prepared and tested under lateral impact loading. In addition to UHPFRC filled DST members, normal strength concrete (NSC) filled DST member was also tested for comparison. Other investigated parameters in this study include the impact energy, the outer steel tube thickness, the inner steel tube thickness, and the presence of axial force. The test results demonstrate that the UHPFRC filled DST members exhibit significantly higher lateral impact resistance capacity than the NSC filled DST member. The impact energy and the outer steel tube thickness significantly affect the lateral impact behavior of UHPFRC filled DST members, while the influence of inner steel tube thickness is insignificant. With the applied axial force in this study, the influence of axial force is also insignificant. Afterwards, numerical model was developed and validated by the present test results. Based on the validated numerical model, the mid-span bending moment distributions and the stress wave propagations were investigated. Finally, parametric analyses were carried out to investigate the influences of different parameters on the lateral impact behavior of UHPFRC filled DST members.
Wei, J, Li, J & Wu, C 2019, 'An experimental and numerical study of reinforced conventional concrete and ultra-high performance concrete columns under lateral impact loads', Engineering Structures, vol. 201, pp. 109822-109822.
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© 2019 Elsevier Ltd This paper presents an experimental and numerical study on the dynamic behaviour of axially-loaded reinforced conventional concrete (RC) and ultra-high performance concrete (UHPC) columns against low-velocity impact loading. The test specimens were divided into two groups with square and circular cross-section shapes, and each group includes both RC and UHPC columns. The impact scenario was modelled with a drop weight falling freely on the column mid-span. Brittle failure with shear plug formation was observed in RC columns while UHPC columns remained a flexure response with minimal damage under severe impact loads. To further interpret the experimental data, detailed finite element (FE) models were developed for RC and UHPC columns. A Continuous Surface Cap Model (CSCM) which accounts for the triaxial material strength, post peak softening and strain rate effect was adopted for UHPC material. After validating the material and structural model based on the testing data, extensive numerical simulations were performed to predict the UHPC column residual loading capacity after lateral impacts. Impact mass-velocity (M-V) diagrams were derived for the UHPC column damage assessment, and analytical formulae which could be easily applied to generate M-V diagrams were derived based on parametric studies.
Wu, P, Wu, C, Liu, Z & Hao, H 2019, 'Investigation of shear performance of UHPC by direct shear tests', Engineering Structures, vol. 183, pp. 780-790.
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© 2019 Elsevier Ltd Ultra-high performance concrete (UHPC) has been applied widely in modern structure construction. The outstanding mechanical properties of UHPC not only enable strong yet slim structural designs but also highlight its potential in protective structural constructions against extreme loads. In this study, the shear transfer behaviors of UHPC are investigated by push-off tests on Z-shaped specimens, investigating the influences of the microsteel fiber volume ratio and stirrup reinforcement ratio on the shear strength, shear slip, and shear crack width of UHPC. The test results indicate that using a microsteel fiber can enhance the shear strength of UHPC specimens. Within a reasonable range of the steel fiber volume ratio (optimum volume ratio ranges from 0% to 2.5% for microsteel fiber), the shear strength and shear slip of UHPC increase significantly, and the shear crack width reduces with an increasing steel fiber volume ratio. Additionally, the ductility, shear strength, and shear slip of UHPC increase significantly, and the shear crack width reduces with increasing stirrup ratio. Finally, the simplified empirical equations for the ultimate shear strengths of UHPC specimens are deduced, and indicate good agreement with the experimental results.
Xu, R & Fatahi, B 2019, 'Impact of In Situ Soil Shear-Wave Velocity Profile on the Seismic Design of Tall Buildings on End-Bearing Piles', Journal of Performance of Constructed Facilities, vol. 33, no. 5, pp. 04019053-04019053.
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© 2019 American Society of Civil Engineers. In this study, a numerical investigation into how the shear wave velocity profile affects the seismic performance of tall buildings and foundations was carried out using FLAC3D software. The in situ soil profile and equivalent average soil profile, which reflect the actual soil shear wave velocity profile and the corresponding uniform time-averaged soil shear wave profile based on the actual profile, respectively, were studied. Overconsolidated soil near the ground surface was considered in the in situ soil profile. A 20-story building supported by an end-bearing pile foundation was designed and simulated. A fully coupled nonlinear dynamic analysis was carried out in the time domain to evaluate the seismic response of the structure and foundation system under strong earthquakes. The variations of the interface parameters with depth around the piles were considered according to the variations in the stiffness of surrounding soil with depth in the numerical model when the in situ soil profile was used. The predicted shear forces, maximum lateral deformation, and maximum interstory drifts of the building are presented and discussed, as are the maximum shear forces, maximum bending moments, and the maximum lateral deformation of the piles. The results indicate that the use of an actual shear wave velocity profile instead of an equivalent average profile gives design engineers the opportunity to optimize their design and achieve cost-effective solutions.
Xu, R & Fatahi, B 2019, 'Novel application of geosynthetics to reduce residual drifts of mid-rise buildings after earthquakes', Soil Dynamics and Earthquake Engineering, vol. 116, pp. 331-344.
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© 2018 Elsevier Ltd Geosynthetics have been used in variety of geotechnical engineering projects, such as ground improvement, erosion control, slope stabilisation and foundation strength improvement and they have been proved to be cost and time effective in many cases. In this study, a geosynthetic reinforced composite soil (GRCS) foundation system is proposed for seismic protection of mid-rise buildings supported by a shallow foundation potentially suffering from residual structural drift or permanent foundation settlement. To evaluate the proposed GRCS, a conventional reinforced concrete moment resisting building sitting on this composite ground under the earthquake excitations of 1978 Tabas, 1994 Northridge and 1995 Kobe was numerically simulated using FLAC3D software. The effect of soil-structure interaction (SSI) was captured using direct method of analysis adopting a three-dimensional numerical model. By adopting direct calculation method, the soil deposit, the geosynthetic reinforcement, the foundation and the structure were simulated simultaneously. Inelastic behaviour of the structure was considered, while hysteretic damping algorithm was adopted representing the variation of the shear modulus and corresponding damping ratio of the soil with cyclic shear strain capturing the energy dissipation characteristics of the soil. Both material and geometry nonlinearities were taken into account at the interface between the foundation and ground surface. The results are then presented in terms of mobilised tensile force in geosynthetic layers, the response spectra at bedrock and ground surface level, the shear force developed in the superstructure, the maximum foundation rocking angle, the maximum lateral deflection, the maximum inter-storey drift, and most importantly the residual inter-storey drift and permanent foundation settlement. The results showed that the proposed GRCS could offer design engineers a rational and cost-effective alternative solution to con...
Xu, S, Wu, C, Liu, Z & Shao, R 2019, 'Experimental investigation on the cyclic behaviors of ultra-high-performance steel fiber reinforced concrete filled thin-walled steel tubular columns', Thin-Walled Structures, vol. 140, pp. 1-20.
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© 2019 This paper presents an experimental investigation on the cyclic behaviors of ultra-high performance steel fiber reinforced concrete filled thin-walled steel tubular columns under combined axial compression and cyclic lateral displacement loading. The failure modes, hysteretic behaviors, envelop diagrams, ductile performance, stiffness degradation and energy dissipation capacity were analyzed in detail. Notably, the cyclic behaviors of referenced high strength concrete and normal strength concrete filled thin-walled steel tubular columns were also studied to get a better illustration of the cyclic behaviors of ultra-high-performance steel fiber reinforced concrete filled thin-walled steel tubular columns. Furthermore, the effects of steel tube thickness, axial compression ratio, volume ratio of steel fiber and slenderness on the cyclic behaviors of ultra-high-performance steel fiber reinforced concrete filled thin-walled steel tubular columns were also investigated in detail. The test results indicate that the high strength concrete filled thin-walled steel tubular columns represent a poor cyclic behavior. However, replacing high strength concrete with ultra-high performance steel fiber reinforced concrete to infill thin-walled steel tubes can get an excellent cyclic behavior. Moreover, the cyclic behavior of ultra-high performance steel fiber reinforced concrete filled thin-walled steel tubular columns is also much better than that of normal strength concrete filled thin-walled steel tubular columns.
Xue, C, Li, W, Li, J & Wang, K 2019, 'Numerical investigation on interface crack initiation and propagation behaviour of self-healing cementitious materials', Cement and Concrete Research, vol. 122, pp. 1-16.
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© 2019 Elsevier Ltd Based on the extended finite element method (XFEM) and cohesive surface (CS) technique, the interface cracks between healing agent and cementitious materials in the self-healing mortar beam under three-point bending are numerically investigated in this study. After obtaining original crack feature using XFEM, a parametric study was conducted to comprehensively discuss effects of the elastic ratio between self-healing agent and cementitious materials, bonding strength and fracture toughness of the self-healing agent-cementitious material interface on crack initiation and propagation. The results reveal that crack initiation seriously degrades stiffness of cementitious materials. Flexible healing agent increases the probability of new crack initiation and healed crack propagation, while stiffer healing agent induces obvious stress concentration around the interface, increasing fracture chance of interfacial zone. The numerical model and methodology developed in this study are useful to investigate the self-healing behaviours and develop high efficient self-healing cementitious materials.
Xue, C, Li, W, Li, J, Tam, VWY & Ye, G 2019, 'A review study on encapsulation‐based self‐healing for cementitious materials', Structural Concrete, vol. 20, no. 1, pp. 198-212.
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Encapsulation‐based self‐healing technology is an effective method for healing the crack‐deteriorated cementitious material. Encapsulation‐based self‐healing initiates by crack occurrence and progresses by chemical reaction of released self‐healing agents in the cracks, which are contained in capsules. In this paper, a review has been conducted on various healing agents, encapsulation techniques, as well as experimental approaches, basing on existing substantial studies. Recently, there is no consistent agreement on the effective criteria for evaluating encapsulation‐based self‐healing and mature solution for increasing the survival ratio of capsules during mixing. However, the polyurethane‐based healing agents filled in glass or ceramic tubes are popularly applied for self‐healing cementitious materials. Besides, the polymer capsules present promising attractions for engineering application. Mechanical strength and durability are the most widely used self‐healing efficiency assessment indexes. On the other hand, nondestructive technique and numerical modeling have also extensively adopted to visualize and evaluate the self‐healing behavior of cementitious materials. However, there are still some challenges, which require further investigations, such as behavior of crack propagation, kinetics of healing agent in discrete crack surfaces, effect of inserted capsules on the mechanical properties of self‐healed cementitious materials.
Yang, G, Jiang, Y, Nimbalkar, S, Sun, Y & Li, N 2019, 'Influence of Particle Size Distribution on the Critical State of Rockfill', Advances in Civil Engineering, vol. 2019, pp. 1-7.
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In order to study the effect of particle size distribution on the critical state of rockfill, a series of large-scale triaxial tests on rockfill with different maximum particle sizes were performed. It was observed that the intercept and gradient of the critical state line in thee−p′plane decreased as the grading broadened with the increase in particle size while the gradient of the critical state line in thep′−qplane increased as the particle size increased. A power law function is found to appropriately describe the relationship between the critical state parameters and maximum particle size of rockfill.
Yang, G, Yan, X, Nimbalkar, S & Xu, J 2019, 'Effect of Particle Shape and Confining Pressure on Breakage and Deformation of Artificial Rockfill', International Journal of Geosynthetics and Ground Engineering, vol. 5, no. 2.
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© 2019, Springer Nature Switzerland AG. The rockfill exhibits a substantial amount of particle breakage when subjected to higher range of stresses. The deformations of rockfill under such excessive stresses often lead to failure and cannot be ignored. The degree of particle breakage is related to the type of the material as well as the particle shape. Based on this, artificially simulated rockfill materials with three different aggregate shapes (prism, cube, and cylinder) were prepared by cement paste-casting method. Through a series of medium-sized triaxial shear tests, the effects of confining pressure and particle shape on the fracture characteristics of the artificial rockfill and its secant modulus were investigated. The useful relationships between particle sphericity and roundness with deformation modulus and particle breakage rate were proposed.
Yang, Y, Wu, C, Liu, Z, Liang, X & Xu, S 2019, 'Experimental investigation on the dynamic behaviors of UHPFRC after exposure to high temperature', Construction and Building Materials, vol. 227, pp. 116679-116679.
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© 2019 Elsevier Ltd Split Hopkinson pressure bar (SHPB) tests were conducted to experimentally study the dynamic behaviors of ultra-high-performance fiber-reinforced concrete (UHPFRC) after being first exposed to elevated temperatures, followed by cooling. The dynamic stress–strain relationships were measured as key parameters to study the effects of high temperature on the dynamic behaviors of fire-damaged UHPFRC. In addition, dynamic increase factor (DIF) values for the dynamic compressive strength were generated. It was found that the strength of UHPFRC increased with the increase in strain rates with high temperatures. A significant difference in the dynamic compressive strength was found under two different temperature scenarios, i.e., elevated temperatures and cooling. Scanning electron microscopy (SEM) analysis was conducted to understand the macroscopic failure phenomenon, element composition and concrete hydration process. The results provide a basis for assessing the impact resistance and anti-collapse resistance of fire-damaged UHPFRC structures.
Yeganeh, N & Fatahi, B 2019, 'Effects of choice of soil constitutive model on seismic performance of moment-resisting frames experiencing foundation rocking subjected to near-field earthquakes', Soil Dynamics and Earthquake Engineering, vol. 121, pp. 442-459.
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© 2019 Elsevier Ltd The current study investigated the extent to which the choice of the soil constitutive models can impact the predicted seismic performance of a 20-story reinforced concrete moment-resisting building with a mat foundation considering the Seismic Soil-Structure Interaction (SSSI). Since the soil, in general, is the weakest material, involved in the commonplace geotechnical engineering projects, a soil constitutive model would be able to rule the dynamic response of the system. In this research, the hardening plasticity-based soil constitutive model, named “hyperbolic hardening with hysteretic damping” in conjunction with the two simple, conventional soil models, namely, the isotropic elastic with hysteretic damping model, and elastic-perfectly plastic Mohr-Coulomb with hysteretic damping model, were invoked in the three-dimensional coupled soil-structure numerical simulations using FLAC3D software. The direct method of analysis was used for analyzing the soil-foundation-structure system in one single step without a need to separately analyze each part of the domain. The cherry-picked earthquake excitations, viz, the 1999 Chi-Chi (Taiwan), and 2011 Kohriyama (Japan), were scaled by means of the widely-used response spectrum matching method as per the design response spectrum of a strong rock. The plastic moment concept was employed so as to assign the elastic-perfectly plastic model to the superstructure and its foundation. Additionally, the strain-compatible shear modulus and damping dependency on the cyclic shear strain were considered via the programmed hysteretic damping algorithm. The numerical predictions included the response spectra at the seismic bedrock and ground surface, base shear forces, shear force distributions along the building height, maximum and permanent foundation displacements, and foundation rocking, plus the flooring lateral deflections and inter-story drifts. The life safety limits for the transient and residual total in...
Yu, C, Wang, H, Wu, Z-X, Sun, W-J & Fatahi, B 2019, 'Analytical Solution for Pollutant Diffusion in Soils with Time-Dependent Dispersion Coefficient', International Journal of Geomechanics, vol. 19, no. 10, pp. 04019109-04019109.
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Yu, Li, Li, Li, Li & Wang 2019, 'Comparative Investigation of Phenomenological Modeling for Hysteresis Responses of Magnetorheological Elastomer Devices', International Journal of Molecular Sciences, vol. 20, no. 13, pp. 3216-3216.
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Magnetorheological elastomer (MRE) is a type of magnetic soft material consisting of ferromagnetic particles embedded in a polymeric matrix. MRE-based devices have characteristics of adjustable stiffness and damping properties, and highly nonlinear and hysteretic force–displacement responses that are dependent on external excitations and applied magnetic fields. To effectively implement the devices in mitigating the hazard vibrations of structures, numerically traceable and computationally efficient models should be firstly developed to accurately present the unique behaviors of MREs, including the typical Payne effect and strain stiffening of rubbers etc. In this study, the up-to-date phenomenological models for describing hysteresis response of MRE devices are experimentally investigated. A prototype of MRE isolator is dynamically tested using a shaking table in the laboratory, and the tests are conducted based on displacement control using harmonic inputs with various loading frequencies, amplitudes and applied current levels. Then, the test results are used to identify the parameters of different phenomenological models for model performance evaluation. The procedure of model identification can be considered as solving a global minimization optimization problem, in which the fitness function is the root mean square error between the experimental data and the model prediction. The genetic algorithm (GA) is employed to solve the optimization problem for optimal model parameters due to its advantages of easy coding and fast convergence. Finally, several evaluation indices are adopted to compare the performances of different models, and the result shows that the improved LuGre friction model outperforms other models and has optimal accuracy in predicting the hysteresis response of the MRE device.
Yu, Y, Dackermann, U, Li, J & Niederleithinger, E 2019, 'Wavelet packet energy–based damage identification of wood utility poles using support vector machine multi-classifier and evidence theory', Structural Health Monitoring, vol. 18, no. 1, pp. 123-142.
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This article presents a novel assessment framework to identify the health condition of wood utility poles. The innovative approach is based on the integration of data mining and machine learning methods and combines advanced signal processing, multi-sensor data fusion and decision ensembles to classify different damage condition types of wood poles. In the proposed framework, wavelet packet analysis is employed to transform captured multi-channel stress wave signals into energy information, which is consequently compressed by principal component analysis to extract a feature vector. Furthermore, support vector machine multi-classifier, optimized by genetic algorithm, is designed to identify the pole condition type. Finally, evidence theory is applied to fuse different assessment results from different sensors for a final decision. For validation of the proposed approach, the wood pole specimens with three common damage condition types are tested using a novel multi-sensor narrow-band frequency-excitation non-destructive testing system in the laboratory. The final experimental analysis results confirm that the proposed approach is capable of making full use of multi-sensor information and providing an effective and accurate identification on types of conditions in wood poles.
Yu, Y, Li, Y, Li, J & Gu, X 2019, 'Characterizing nonlinear oscillation behavior of an MRF variable rotational stiffness device', Smart Structures and Systems, vol. 24, no. 3, pp. 303-317.
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Magneto-rheological fluid (MRF) rotatory dampers are normally used for controlling the constant rotation of machines and engines. In this research, such a device is proposed to act as variable stiffness device to alleviate the rotational oscillation existing in the many engineering applications, such as motor. Under such thought, the main purpose of this work is to characterize the nonlinear torque-angular displacement/angular velocity responses of an MRF based variable stiffness device in oscillatory motion. A rotational hysteresis model, consisting of a rotatory spring, a rotatory viscous damping element and an error function-based hysteresis element, is proposed, which is capable of describing the unique dynamical characteristics of this smart device. To estimate the optimal model parameters, a modified whale optimization algorithm (MWOA) is employed on the captured experimental data of torque, angular displacement and angular velocity under various excitation conditions. In MWOA, a nonlinear algorithm parameter updating mechanism is adopted to replace the traditional linear one, enhancing the global search ability initially and the local search ability at the later stage of the algorithm evolution. Additionally, the immune operation is introduced in the whale individual selection, improving the identification accuracy of solution. Finally, the dynamic testing results are used to validate the performance of the proposed model and the effectiveness of the proposed optimization algorithm.
Yu, Y, Subhani, M, Dackermann, U & Li, J 2019, 'Novel Hybrid Method Based on Advanced Signal Processing and Soft Computing Techniques for Condition Assessment of Timber Utility Poles', Journal of Aerospace Engineering, vol. 32, no. 4, pp. 04019032-04019032.
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© 2019 American Society of Civil Engineers. Recently, a variety of nondestructive evaluation (NDE) approaches have been developed for health assessment and residual capacity estimation of timber structures. Among these methods, guided wave (GW)-based techniques are highly regarded as effective tools for potential use in real situations. Nevertheless, because it is hard to comprehensively grasp the behavior of wave propagation in a wood structure, existing NDE-based techniques mainly depend on an oversimplified hypothesis, which can result in inaccurate or even misleading results in practice. Understanding the complex behavior of GW propagation in wood structures and extracting appropriate information from captured GW signals is a key for successful assessments of in situ conditions of timber structures. This paper analyzes the existing feature extraction and damage detection algorithms, and proposes a novel approach based on an integration of wavelet packet transform (WPT) and ensemble empirical mode decomposition (EEMD) for extracting damage-sensitive patterns, and then a soft computing method like support vector machine (SVM) for pole condition identification. In the proposed method, GW signals measured from a multisensing system with pole health condition as the baseline are divided into a series of subfrequency bands based on WPT. Then EEMD is adopted to extract the intrinsic mode functions (IMFs) that possess the features extracted at corresponding subfrequency bands. Hence, the IMF component was segregated from the original signals of tested poles, and the IMF Shannon entropy was employed to build up the feature vector to effectively demonstrate the health condition. To decrease the size of the feature vector and avoid multiple collinearity among obtained patterns, principal component analysis was employed and entropy information in the feature vector was replaced with main principal components, which will be employed as input variables of the dev...
Yu, Y, Wang, C, Gu, X & Li, J 2019, 'A novel deep learning-based method for damage identification of smart building structures', Structural Health Monitoring, vol. 18, no. 1, pp. 143-163.
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In the past few years, intelligent structural damage identification algorithms based on machine learning techniques have been developed and obtained considerable attentions worldwide, due to the advantages of reliable analysis and high efficiency. However, the performances of existing machine learning–based damage identification methods are heavily dependent on the selected signatures from raw signals. This will cause the fact that the damage identification method, which is the optimal solution for a specific application, may fail to provide the similar performance on other cases. Besides, the feature extraction is a time-consuming task, which may affect the real-time performance in practical applications. To address these problems, this article proposes a novel method based on deep convolutional neural networks to identify and localise damages of building structures equipped with smart control devices. The proposed deep convolutional neural network is capable of automatically extracting high-level features from raw signals or low-level features and optimally selecting the combination of extracted features via a multi-layer fusion to satisfy any damage identification objective. To evaluate the performance of the proposed deep convolutional neural network method, a five-level benchmark building equipped with adaptive smart isolators subjected to the seismic loading is investigated. The result shows that the proposed method has outstanding generalisation capacity and higher identification accuracy than other commonly used machine learning methods. Accordingly, it is deemed as an ideal and effective method for damage identification of smart structures.
Zhang, G, Li, Y, Wang, H & Wang, J 2019, 'Rheological Properties of Polyurethane-Based Magnetorheological Gels', Frontiers in Materials, vol. 6.
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© 2019 Zhang, Li, Wang and Wang. The paper tests the influence of mass fractions of carbonyl iron particles (CIPs) on the rheological properties of magnetorheological (MR) gels. Polyurethane-based MR gels with different weight fraction of CIPs, i.e., 40, 60, and 80%, were firstly prepared by mechanical mixing, respectively. The changes of shear stress and viscosity with shear rate under different magnetic flux density were tested and analyzed. It was found that the shear stress increases with mass fraction under magnetic flux density. The viscoelastic properties of MRGs were achieved by oscillatory shear measure. The effects of strain amplitude and frequency on viscoelastic of MRGs under different magnetic flux density were measured and analyzed. The study results shown that the elastic characteristics become more obvious with the increase of CIPs mass fraction. However, it has opposite effect on the viscous properties of materials.
Zhang, J-Z, Li, G-Q, Jiang, J & Zhang, W-J 2019, 'Collapse resistance of composite framed-structures considering effects of slab boundary restraints', Journal of Constructional Steel Research, vol. 158, pp. 171-181.
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Zhang, X, Fatahi, B, Khabbaz, H & Poon, B 2019, 'Assessment of the Internal Shaft Friction of Tubular Piles in Jointed Weak Rock Using the Discrete-Element Method', Journal of Performance of Constructed Facilities, vol. 33, no. 6, pp. 04019067-04019067.
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© 2019 American Society of Civil Engineers. This study focuses on the internal shaft friction of open-ended tubular piles induced by jointed weak rock plugs. To investigate the bearing mechanism of the plug, push-up load tests were carried out on the jointed mudstone inside a tubular pile. The discrete-element method (DEM) was used in order to consider heterogeneity and to reproduce the discrete nature of the rock mass. A flat-joint model was used to reproduce the mechanical behavior of mudstone, and a smooth-joint contact model was used to replicate natural joints. The push-up load tests were carried out using the calibrated properties of a weak mudstone. The effects of joint density and joint dip were examined in detail and, as expected, the push-up force of the rock plug was influenced by the joint properties because joint density and joint dip had to some extent affected the plug resistance. The existing joints reduced the push-up force when the joints were steep, whereas the horizontal joints had a minimal effect on altering the inner shaft friction compared with the intact rock mass. The reduced friction along the pile was amplified with joint density, while the exponential increase of vertical stress from the top of the rock plug to the bottom revealed that the inner shaft resistance was mainly mobilized at the bottom portion of the rock plug. The findings of this study increase our understanding of joint dip and joint density affecting the internal shaft resistance of open-ended tubular piles; this knowledge can be used further to develop a design methodology for open-ended tubular piles in weak rock while assessing plugging effects.
Zhao, H, Tao, M, Li, X, Cao, W & Wu, C 2019, 'Estimation of spalling strength of sandstone under different pre-confining pressure by experiment and numerical simulation', International Journal of Impact Engineering, vol. 133, pp. 103359-103359.
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© 2019 Elsevier Ltd Spalling failure is a common underground engineering disaster, particularly in deep environments with high geo-stress and strong stress disturbances. Therefore, the further investigation of the spalling behaviour of rock under different pre-confining pressures is of considerable importance. In the presented work, a modified split Hopkinson pressure bar (SHPB) system is modified with a pre-confining loading device that can apply pre-static loads to Φ50 mm × 300 mm specimens. The system is employed to study the spalling characteristics of rock specimens subjected to full pre-confining pressure. Spalling tests of Φ50 mm × 300 mm rock specimens under different pre-confining pressures were conducted. The experimental results indicated that spalling failure was influenced by pre-confining pressure. Furthermore, numerical simulations with the same loading conditions as the experiments were conducted using the finite element software, LS-DYNA, and the spalling strengths of the rock specimens under different pre-confining pressures were obtained based on the improved stress wave analysis method. The results indicated that the stress wave analysis method in view of numerical simulation can effectively be used for calculating the spalling strength of rock and rock-like material under pre-confining pressure. The spalling strength of the rock specimens increased first and then decreased as the pre-confining pressure increased.
Zhao, L-S, Zhou, W-H, Geng, X, Yuen, K-V & Fatahi, B 2019, 'A closed-form solution for column-supported embankments with geosynthetic reinforcement', Geotextiles and Geomembranes, vol. 47, no. 3, pp. 389-401.
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© 2019 Elsevier Ltd Soil arching effect results from the non-uniform stiffness in a geosynthetic-reinforced and column-supported embankment system. However, most theoretical models ignore the impact of modulus difference on the calculation of load transfer. In this study, a generalized mathematical model is presented to investigate the soil arching effect, with consideration given to the modulus ratio between columns and the surrounding soil. For simplification, a cylindrical unit cell is drawn to study the deformation compatibility among embankment fills, geosynthetics, columns, and subsoils. A deformed shape function is introduced to describe the relationship between the column and the adjacent soil. The measured data gained from a full-scale test are applied to demonstrate the application of this model. In the parametric study, certain influencing factors, such as column spacing, column length, embankment height, modulus ratio, and tensile strength of geosynthetic reinforcement, are analyzed to investigate the performance of the embankment system. This demonstrates that the inclusion of a geosynthetic reinforcement or enlargement of the modulus ratio can increase the load transfer efficiency. When enhancing the embankment height or applying an additional loading, the height of the load transfer platform tends to be reduced. However, a relatively long column has little impact on the load transfer platform.
Zhu, S, Li, JC, Casciati, S & Li, J 2019, 'Special Issue on Smart Devices for Structural Control:Preface', Smart Structures and Systems, vol. 24, no. 1, p. I.
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Aghayarzadeh, M & Khabbaz, H 1970, 'Numerical simulation of concrete pile groups' response bored in cemented sand deposit under axial static load testing', E3S Web of Conferences, International Symposium on Deformation Characteristics of Geomaterials, EDP Sciences, Glasgow, UK, pp. 16011-16011.
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For a safe foundation to perform as desired, the ultimate strength of each pile must fulfil both structural and geotechnical requirements. Pile load testing is considered as a direct method of determining the ultimate bearing capacity of a pile. Pile groups are commonly used in foundation engineering and due to the difficulties and cost of full-scale load tests, most pile group tests are scaled down regardless of whether performed in the field or laboratory. In this paper, it is aimed to simulate the behaviour of concrete bored pile groups under axial static load testing using PLAXIS 3D software and to compare the obtained results with measured curves in an experimental study introduced in the literature. In numerical simulation, to account for the stiffness variation existing inside the pile group and to achieve a reasonable correlation between measured and predicted load-settlement curves three different analyses, including linear elastic, completely non-linear, and a combination of non-linear and linear analyses were performed. The results indicate that the combined non-linear and linear analysis seems a suitable analysis for pile group behaviour prediction.
Aghayarzadeh, M, Khabbaz, H & Fatahi, B 1970, 'Evaluation of Reaction Piles Effect on Test Piles in Static Load Testing Using Three-Dimensional Numerical Analysis', ASTM Special Technical Publication, International Conference on Stress Wave Theory and Testing Methods for Deep Foundations, ASTM International, San Diego, California, USA, pp. 68-80.
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Copyright © 2019 by ASTM International. Static load testing includes the direct measurement of pile head displacements when a physical test load is applied. It is known as the most fundamental form of pile load testing and generally considered as a benchmark for pile performance assessment. During static load testing, the load is commonly applied using a hydraulic jack acting against a reaction beam, which is restrained by an anchorage system. The anchorage system may be in the form of cable anchors or reaction piles installed into the ground to provide tension resistance. In this paper, PLAXIS 3D software incorporating elastic-perfectly-plastic Mohr-Coulomb and hardening-soil constitutive models is initially used to simulate a real static load test conducted in stiff overconsolidated clay. Then, in order to assess the effect of the reaction system on the test results, a similar model using the hardening-soil model is simulated. In the three-dimensional model, different numbers of reaction piles, identical to the test pile, are located in different distances from the test pile. Subsequently, the influences of spacing, length, diameter of reaction piles, and type of reaction piles on the load-displacement behavior of test piles are assessed. This paper can provide insight to practicing civil engineers on how to design the loading systems for static pile load tests.
Bolaji, BO, Adeleke, AE, Adu, MR, Olanipekun, MU & Akinnibosun, E 1970, 'Theoretical Investigation of Energy-Saving Potential of Eco-Friendly R430A, R440A and R450A Refrigerants in a Domestic Refrigerator', Iranian Journal of Science and Technology, Transactions of Mechanical Engineering, International Symposium on Automation and Robotics in Construction, Springer Science and Business Media LLC, Sydney Australia, pp. 103-112.
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The objective of this study is to explore an optimal strategy on energy consumption for a direct expansion (DX) air-conditioning system by using a refrigerant pump in the liquid line to allow the system to operate at a lower condensing pressure. An existing DX rooftop package of a commercial building located in a hot and dry climate zone is used for data collection. The theoretical-empirical modelling approach is used to obtain system model, from which the proposed strategy is formulated. A numerical algorithm is developed to analyse the system transient performance, using an iterative loop. As a minimum pressure differential is required across the expansion device, liquid pressure amplification (LPA) devices can be used on DX systems that operate with fixed head pressure control. They can be fitted to new or existing systems. Results show that the LPA approach is more effective when the ambient temperature is falling, with electricity saving around 25.3% in average.
Bonthu, RK, Aguilera, RP, Pham, H, Phung, MD & Ha, QP 1970, 'Energy Cost Optimization in Microgrids Using Model Predictive Control and Mixed Integer Linear Programming', 2019 IEEE International Conference on Industrial Technology (ICIT), 2019 IEEE International Conference on Industrial Technology (ICIT), IEEE, Melbourne, Australia, pp. 1113-1118.
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© 2019 IEEE. This paper presents a model predictive control (MPC) approach based on the mixed integer linear programming (MILP) to develop an optimal power management strategy (PMS) for minimizing the electricity bill of commercial buildings in a domestic on-grid system. The optimal PMS is first formulated as a MILP-MPC with time-varying constraints. The constraints are then linearized at each sampling time so that a receding horizon principle can be used to determine the control input applied to the plant and update the model. The time-varying efficiency of power electronic converters is evaluated for each time interval and assumed to be persistent for the prediction time horizon. The numerical results show that the proposed MILP-MPC strategy with variable efficiency is effective in utilizing photovoltaic power generation to save the cost on electricity for buildings.
Butcher, R & Sirivivatnanon, V 1970, 'Influence of shape and grading of manufactured sand on the workability and compressive strength of concrete', FIB 2018 - Proceedings for the 2018 fib Congress: Better, Smarter, Stronger, pp. 3050-3060.
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In this study, two methods of producing manufactured sands from the same rock source were evaluated in terms of the resulting shape and grading of the sands, and their effects on the workability and compressive strength of cement mortar and concrete. The two sands were used to blend with a natural sand to produce cement mortars at fixed sand to cement (S/C) and water to cement ratio (W/C). The shape and grading of the two sands were found to affect the New Zealand flow cone time and air void (RMS T279) and consequently the flow and compressive strength of the mortars. The sand blends were also used to produce a standard grade concrete with equal slump. The efficiency of the two sands in concrete production was measured in term of water demand of the concrete. The economic viability of each sand production method is reflected in comparing the quantity of cement and fly ash required to produce each cubic meter of a standard grade concrete.
Dang, LC & Khabbaz, H 1970, 'Experimental Investigation on the Compaction and Compressible Properties of Expansive Soil Reinforced with Bagasse Fibre and Lime', Recent Advancements on Expansive Soils: Proceedings of the 2nd GeoMEast International Congress and Exhibition on Sustainable Civil Infrastructures, Egypt 2018 – The Official International Congress of the Soil-Structure Interaction Group in Egypt (SSIGE), GeoMEast International Congress and Exhibition on Sustainable Civil Infrastructures, Egypt 2018 – The Official International Congress of the Soil-Structure Interaction Group in Egypt (SSIGE), Springer International Publishing, Egypt, pp. 64-78.
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This paper presents a laboratory investigation into the mechanical characteristics of expansive soil reinforced with randomly distributed bagasse fibre and lime combination. Bagasse fibre, an agricultural waste by-product left after crushing of sugar-cane for juice extraction, was employed in this investigation as a reinforcing component for expansive soil reinforcement. Several series of laboratory experiments including standard compaction and consolidation tests were carried out on untreated soil and soil samples mixed with various contents of bagasse fibre in a wide range from 0% to 2% and a certain amount of 2.5% lime. The experimental results were used to comprehend the effects of adding bagasse fibre on the compaction and compressible properties of fibre reinforced soils with lime stabilisation. The compaction test results indicate that the addition of bagasse fibre, hydrated lime, and their combination decreased the dry density of stabilised soils. Moreover, the obtained results of the consolidation tests reveal that the reinforcement of expansive soil with bagasse fibre improved the pre-consolidation pressure, meanwhile tended to reduce the compression characteristics of the lime stabilised soils as bagasse fibre content increased from 0% to 1%. However, an excessive increase in bagasse fibre content beyond 1% to 2% was found to result in a slight reduction of the compressibility of lime-soil mixtures reinforced with bagasse fibre. The findings of this research provide a deeper insight into promoting applications of an agricultural waste by-product of bagasse fibre as a low-cost and eco-friendly material for treatment of expansive soils and fill materials for sustainable construction development in the field of civil infrastructure foundations.
Dang, LC & Khabbaz, H 1970, 'Shear Strength Behaviour of Bagasse Fibre Reinforced Expansive Soil', IACGE 2018, International Conference on Geotechnical and Earthquake Engineering 2018, American Society of Civil Engineers, Chongqing, China, pp. 393-402.
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© 2019 American Society of Civil Engineers. This paper presents an experimental investigation on the shear strength behaviour of expansive soil reinforced with bagasse fibre. Bagasse fibre, an agricultural waste by-product left after crushing of sugar-cane for juice extraction, was employed in this study as a reinforcing component for expansive soil reinforcement. The expansive soil used in this investigation was collected from Queensland, Australia. To experimentally investigate the influence of bagasse fibre reinforcement on the shear strength of expansive soil, a series of non-reinforced and fibre reinforced soil samples was prepared by changing randomly distributed bagasse fibre content from 0% to 2%. An array of intensive experimental tests using triaxial compression apparatus was carried out and its results are presented and discussed in further detail. The experimental results reveal that bagasse fibre reinforcement exhibited significant effects on shear strength characteristics of reinforced soils in terms of relationships between deviatoric stress and axial shear strain, ultimate deviatoric strength, and shear strength parameters.
El-Hawat, O, Fatahi, B & Edmonds, C 1970, 'Earthquake Geotechnical Engineering for Protection and Development of Environment and Constructions', 7th International Conference on Earthquake Geotechnical Engineering, CRC Press, Roma, Italy, pp. 2241-2248.
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Gowripalan, N, Cao, J, Sirivivatnanon, V & South, W 1970, 'Assessment of ASR expansions using an ultra-accelerated test', 29th Biennial Conference of the Concrete Institute of Australia, 29th Biennial Conference of the Concrete Institute of Australia, Sydney Australia.
Hoang, VT, Phung, MD, Dinh, TH, Zhu, Q & Ha, QP 1970, 'Reconfigurable Multi-UAV Formation Using Angle-Encoded PSO', 2019 IEEE 15th International Conference on Automation Science and Engineering (CASE), 2019 IEEE 15th International Conference on Automation Science and Engineering (CASE), IEEE, Vancouver, BC, Canada, pp. 1670-1675.
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© 2019 IEEE. In this paper, we propose an algorithm for the formation of multiple UAVs used in vision-based inspection of infrastructure. A path planning algorithm is first developed by using a variant of the particle swarm optimisation, named θ-PSO, to generate a feasible path for the overall formation configuration taken into account the constraints for visual inspection. Here, we introduced a cost function that includes various constraints on flight safety and visual inspection. A reconfigurable topology is then added based on the use of intermediate waypoints to allow the formation to avoid collision with obstacles during operation. The planned path and formation are then combined to derive the trajectory and velocity profiles for each UAV. Experiments have been conducted for the task of inspecting a light rail bridge. The results confirmed the validity and effectiveness of the proposed algorithm.
Le, TM, Dang, LC & Khabbaz, H 1970, 'Combined Effects of Bottom Ash and Lime on Behaviour of Expansive Soil', Recent Advancements on Expansive Soils, International Congress and Exhibition on Sustainable Civil Infrastructures, Springer International Publishing, Cairo, Egypt, pp. 28-44.
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This study illustrates the effectiveness of combining bottom ash and hydrated lime to enhance the engineering properties of expansive soil. The bottom ash was collected from Eraring Power Station in New South Wales, Australia, as a by-product of coal-fired power stations, and soil specimens were used as artificial soil including kaolinite, bentonite and fine sand in a reasonable ratio to stimulate soil samples with characteristics of expansive soil. The stabilised soil samples were prepared by altering the bottom ash content from 0% to 30% on a dry weight basis of expansive soil as well as with constant percentage of 5% in hydrated lime. Through conducting a series of experimental tests including linear shrinkage and unconfined compressive strength (UCS) in various curing time, the shrinkage and strength behaviour of treated soils were investigated and compared with untreated soil samples. The results revealed that the combination of bottom ash and hydrated lime significantly reduced the linear shrinkage, while it increased the strength of expansive soil. The use of bottom ash alone is not recommended due to a slight increase of linear shrinkage and a minor negative impact on the soil strength. The optimum content of combined bottom ash and hydrated lime to stabilise expansive soils is also presented.
Le, TM, Dang, LC & Khabbaz, H 1970, 'Strength Characteristics of Lime and Bottom Ash Reinforced Expansive Soils', Geo-Congress 2019, Eighth International Conference on Case Histories in Geotechnical Engineering, American Society of Civil Engineers, Philadelphia, Pennsylvania, pp. 352-362.
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© 2019 American Society of Civil Engineers. The primary aim of study is to evaluate the influence of hydrated lime and bottom ash on strength properties of expansive soil by two different kinds of dry-weight-based ratios. In this research, bottom ash is used as a stabilizing agent for expansive soil stabilization due to the potential benefits of its additional pozzolanic components in combination of hydrated lime. Bottom ash is a by-product of coal-fired process which was collected from Eraring Power Station in New South Wales, Australia. Meanwhile, expansive soils were artificially prepared using a proper combination of kaolinite, bentonite, and Sydney fine sand to constitute soil samples typically representing expansive soil in the region. To determine the optimum combination ratio of bottom ash to lime to stabilize expansive soil, different contents of randomly distributed bottom ash from 5% to 30% were mixed with soil and 5% hydrated lime to investigate the engineering behaviour of stabilized expansive soils. It is noted that the additive contents of lime and bottom ash, adopted in this study, were calculated based on both the dry weight of soil alone and the total weight of bottom ash-lime-soil admixture for the comparison purpose. The results of indirect tensile (IDT) strength and California bearing ratio (CBR) tests after various curing times are presented and discussed. The experimental findings show that a ratio of 5% lime to 20% bottom ash mixed with expansive soil is considered as their optimum combination ratio for achieving the maximum bearing capacity and tensile strength for soil-dry-weight-based additives. However, the optimum combination ratio of 5% lime to 25% bottom ash is determined in the case of the entire mixture-dry-weight-based additives. It is concluded that applying the latter optimum ratio to a combination of lime and bottom ash can improve the expansive soil strength better than the former.
Li, J & Wu, C 1970, 'Experimental and numerical study on Basalt scale aluminium foam', 7th International Conference on Protection of Structures against Hazards, Hanoi.
Li, W, Luo, Z, Xiao, J & Shah, SP 1970, 'Impact behaviors of recycled aggregate concrete with nanoparticles', FIB 2018 - Proceedings for the 2018 fib Congress: Better, Smarter, Stronger, pp. 3984-3992.
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A 100 mm-diameter split Hopkinson pressure bar (SHPB) was used to investigate effects of nanoparticles on the dynamic mechanical properties of recycled aggregate concrete (RAC) under impact loading. The nano-SiO2 (NS) and nano-CaCO3 (NC) were incorporated to replace cement by mass of 1 and 2% in RACs. The impact velocities were set as 7.7, 9.8 and 11.6 m/s in the SHPB tests. The effects of nanoparticles on failure patterns, compressive strengths, elastic modulus, peak strain and dynamic increase factor (DIF) of RACs under different strain rates were analyzed and discussed. The results show that nanomodified RACs exhibit higher both quasi-static and dynamic compressive strengths compared to control RAC. Dynamic elastic modulus of RAC seems not to be affected by nanoparticles dosages and impact velocities. Compared to NC, NS is more effective in improving dynamic compressive strengths of RAC.
Liu, J & Wu, C 1970, 'Numerical study of ceramic balls protected ultrahigh performance concrete targets subjected to projectile impact', 13th International Conference on Shock and Impact Loads on Structures, SILOS 2019, pp. 325-334.
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Ceramic materials have excellent mechanical properties such as light weight, great hardness and high compressive strength. This paper presents a numerical study on dynamic response of ceramic balls protected ultra-high performance concrete (UHPC) targets subjected to the high-velocity rigid projectile impact using the coupled smoothed particle hydrodynamics-finite element (SPH-FE) method in LS-DYNA. Numerical models are firstly validated, and then parametric studies are conducted to explore the effect of diameter, spatial arrangement and material type of ceramic balls as well as the impact position on the dynamic performance of UHPC targets. Compared with other existing UHPC slabs at the striking velocities from 500 m/s to 850 m/s, UHPC slabs protected with 6-layer hex-pack arranged ceramic balls with the diameter of 20 mm is most effective in terms of reducing the depth of penetration (DOP).
Lyu, W, Cheng, X & Wang, J 1970, 'Adaptive Compensation H∞ Filter with Convergence Criterion for SINS' Transfer Alignment', 2019 IEEE 10TH ANNUAL UBIQUITOUS COMPUTING, ELECTRONICS & MOBILE COMMUNICATION CONFERENCE (UEMCON), IEEE 10th Annual Ubiquitous Computing, Electronics and Mobile Communication Conference (UEMCON), IEEE, NY, Columbia Univ, New York, pp. 1135-1144.
Nguyen, TN, Yu, Y, Li, J, Gowripalan, N & Sirivivatnanon, V 1970, 'Mechanical properties of ASR affected concrete: a critical review', Concrete 2019, Concrete 2019, Sydney.
Nsiah-Baafi, E, Vessalas, K, Thomas, P & Sirivivatnanon, V 1970, 'Investigating the Alkali Threshold of Potentially Reactive Aggregates for Use in ASR Risk-Free Concretes', 29th Biennial National Conference of the Concrete Institute of Australia, Sydney.
Nsiah-Baafi, E, Vessalas, K, Thomas, P & Sirivivatnanon, V 1970, 'Investigation of Alkali Threshold Limits and Blended Aggregate in ASR Risk-Assessed Concretes', Concrete New Zealand Conference 2019, Concrete New Zealand Conference, ConcreteNZ, Dunedin, New Zealand.
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Concrete structures are designed for a specific design life to tolerate deterioration caused from various aggressive environmental loads such as carbon dioxide, chloride and aggressive soil conditions. The approach to prevent deterioration in concrete due to alkali-silica reaction (ASR) is by the avoidance of any such dissolution reaction taking place in concrete. ASR can in part be prevented by limiting the alkali content and restricting the use of potentially reactive aggregates. In this paper, the alkali threshold of several aggregates originating from New Zealand were determined using a modified version of RILEM AAR-3.2 and AAR-7.1. The AAR-2 accelerated mortar bar test (AMBT at 80°C) and AAR-3.2 concrete prism test (CPT at 38°C) were replaced with Australian Standard AS 1141.60.1 and 60.2 test methods, respectively, to evaluate expansion. Additional accelerated CPT in accordance with AAR-4.1 (ACPT at 60°C) was also conducted to examine the adequacy of shortening the test period. Petrographic examination taken before and after expansion testing was also carried out to qualify the presence of reactive silica and ASR gel contributing to expansion. The findings of this study suggest the potential for specifying the alkali threshold in concrete based on the reactivity classification of aggregates allowing a relaxation of the CCANZ Technical Report TR 3 alkali limit of 2.5 kg/m3 that is currently in place in New Zealand. This approach allows greater flexibility in the use of potentially reactive aggregates as sustainable concreting making materials.
Nsiah-Baafi, E, Vessalas, K, Thomas, P & Sirivivatnanon, V 1970, 'Mitigating Alkali Silica reactions in the absence of SCMs: A review of empirical studies', FIB 2018 - Proceedings for the 2018 fib Congress: Better, Smarter, Stronger, The International Federation for Structural Concrete 5th International fib Congress, Melbourne, pp. 3829-3844.
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The mechanism and severity of alkali-silica reaction (ASR) is subjective to the conditions of the availability of moisture and sufficient alkali content, and the presence of reactive aggregates. Since the 1940s, key focus has been placed on the reduction of alkali content by way of addition of supplementary cementitious materials (SCMs). However, the cost of SCMs and the realization that the availability of these materials could become limited in the untold future has influenced some researchers to investigate the development of protocols for the use of aggregates minimizing the likelihood of potential severe ASR. This paper presents a summary and review of the various strategies that have been adopted in recent years for the mitigation of ASR without utilising the addition of SCMs.
Pham Ngoc, T, Fatahi, B & Khabbaz, H 1970, 'Impact of Liquid Whey Waste on Strength and Stiffness of Cement Treated Clay', New Developments in Soil Characterization and Soil Stability, Civil Infrastructures Confronting Severe Weathers and Climate Changes Conference, Springer International Publishing, Hangzhou, China, pp. 1-10.
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The reuse of whey waste, a by-product of the dairy industry, is an emerging issue due to the environmental impacts. Some previous experimental studies have indicated that whey waste can be used as an admixture for cement-based materials, including mortar and concrete, to reduce the setting time and increase the workability, thus reduce the amount of required cement. However, influence of whey waste on cemented soil has not received sufficient attention. This study investigates variations of unconfined compressive strength (UCS) and Young's modulus (E) of cemented Kaolin clay when water in cement slurry was replaced by different whey waste proportions. Unconfined compression tests were conducted on treated specimens after two different curing times, namely 14 days and 56 days. Stress-strain relationship in each test was used to compute UCS and E at different dosages of cement and whey waste. Results of the experiments show improvements of UCS and E only for specimens when less than 10% water in cement slurry was replaced by liquid whey waste at 56 day-curing age, regardless of cement dosage. For the other cases, the presence of whey waste resulted in reductions of both UCS and E, indicating that although whey waste can be used to improve mechanical properties of cement treated clay, the optimum dosage should be selected very carefully to minimize the adverse effects. Different responses of UCS and E with curing age, dosages of cement and liquid whey waste are explained while discussing about the effects of lactose (milk sugar) available in whey waste acting as a retarding agent.
Pshtiwan Shakor, Shami Nejadi & Gavin Paul 1970, 'An Investigation into the Effects of Deposition Orientation of Material on the Mechanical Behaviours of the Cementitious Powder and Gypsum Powder in Inkjet 3D Printing', Proceedings of the International Symposium on Automation and Robotics in Construction (IAARC), 36th International Symposium on Automation and Robotics in Construction, International Association for Automation and Robotics in Construction (IAARC), Banff, AB, Canada, pp. 42-49.
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© 2019 International Association for Automation and Robotics in Construction I.A.A.R.C. All rights reserved. Three-Dimensional Printing (3DP) is widely used and continues to be rapidly developed and adopted, in several industries, including construction industry. Inkjet 3DP is the approach which offers the most promising and immediate opportunities for integrating the benefits of additive manufacturing technic into the construction field. The ability to readily modify the orientation angle that the printed material is deposited is one of the most advantageous features in a 3DP scaffold compared with conventional methods. The orientation angle has a significant effect on the mechanical behaviours of the printed specimens. Therefore, this paper focuses on printing in different orientations somehow to compare various mechanical properties and to characterise a selection of common construction materials including gypsum (ZP 151) and cement mortar (CP). The optimum strength for the gypsum specimens in compression and flexural strength was observed in the (0° and 90°) and (0°) in the X-Z plane, respectively. According to the experimental results, the compression and flexural strength for ZP 151 are recorded at (11.59±1.18 and 11.78±1.19) MPa and 15.57±0.71 MPa, respectively. Conversely, the highest strength in compression and flexural strength are observed in the (90°) and (0°) degrees in the X-Z plane for the cement mortar, respectively. Moreover, it has been discovered that the compression and flexural strengths for CP are recorded as 19.44±0.11 MPa and 4.06±0.08 MPa, respectively. In addition, the dimensional effect for various w/c ratio has been monitored and examined.
Ranjbar Zahedani, M, Keshavarzi, A, Khabbaz, H & Ball, J 1970, 'Flow Structures Around a Circular Bridge Pier with a Submerged Prismat Upstream', World Congress on Civil, Structural, and Environmental Engineering, The 4th World Congress on Civil, Structural, and Environmental Engineering, Avestia Publishing.
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Previous investigations have indicated that local scour around bridge piers and abutments causes around 60% of waterway bridge failures. In order to decrease the potential of pier-scour failure, the authors previously proposed an upstream prism as a new countermeasure against local scour. The proposed prism was examined in a comprehensive experimental program to find the most efficient size, submergence ratio, and installation location of the prism. The experimental results showed that the submerged prism could reduce around 40% of the maximum scour depth, and 60% of the scour-hole volume. In this study, in order to find out how this submerged prism affects the flow structure around the pier and reduces the pier-scour, the flow structure analysis was conducted using particle image velocimetry (PIV). The velocity components were measured for two cases of a single circular pier with and without the submerged prism. Analysis of the results indicated that the proposed prism could change the flow structure at the upstream and downstream of the pier. In fact, this submerged prism formed a wake region behind itself, and the bridge pier was located at this wake region. The produced wake resisted the down-flow at the upstream side of the pier and also disturbed the formation of the horseshoe vortices around the pier. In addition, this submerged prism reduced the strength of wake vortices behind the pier. Consequently, the pier-scour was significantly reduced by the substantial changes in the flow structure.
Ren, F, Wu, C & Lok, TS 1970, 'Preface', 13th International Conference on Shock and Impact Loads on Structures, SILOS 2019, p. iv.
Roboredo, C, Thomas, P, Vessalas, K & Sirivivatnanon, V 1970, 'Alkali limit in cement with supplementary cementing materials - A review', FIB 2018 - Proceedings for the 2018 fib Congress: Better, Smarter, Stronger, The International Federation for Structural Concrete Congress, Conrete Institute, Melbourne, pp. 3702-3708.
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The alkali silica reaction (ASR) may cause deleterious cracking in concretes as a result of the reactions of reactive aggregates in concrete systems that contain elevated alkali contents. Current strategies applied in the mitigation of ASR are based on limiting the alkali content (Na2Oe) of the cement and concrete and through the screening of aggregates with additional surety provided by the use of supplementary cementitious materials (SCMs) in the partial replacement of cement. These strategies pose significant issues for the construction materials industry through increased manufacturing costs and reduction in volumes of viable raw materials that meet the imposed criteria. The effective mitigation of deleterious ASR using SCMs should change the focus of regulators and standards authorities to risk management through the assessment of the risk profile of a concrete mix in a particular application. Using a risk profile to assess alkali limits has the potential to relax alkali limits in cements. To achieve this aim a deep understanding of ASR in cement-SCM-aggregate concrete mixes is required through laboratory testing correlated with long-term field performance. This paper reviews ASR, reactivity assessment of aggregates and the role of SCMs in ASR mitigation and proposes a change in the focus to a balanced alkali limit based on assessed risk for the occurrence of deleterious ASR.
Sarikaya, A, Erkmen, RE, Gowripalan, N, Sirivivatnanon, V & South, W 1970, 'A Plastic-Damage Model for Concrete under Cyclic Loads', Concrete 2019, Concrete 2019, Sydney, Australia.
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A constitutive model based on a novel coupled elastoplastic-damage framework is adopted for the modelling of concrete under cyclic loads. Coupled elastoplastic-damage models have been used to capture both the material degradation and the permanent deformations under inelastic deformations. In this study, a multisurface plasticity framework is implemented for the modelling of concrete under compressive and tensile cyclic loads. The elastoplastic-damage framework is based on the ‘direct-coupling’ method in which an a-priori relationship between the total strain and the damage strain is postulated. The model is easy to calibrate since it utilises the same yield and potential functions for plasticity and damage calculations. Concrete is modelled using a pair of yield surfaces in order to capture its compressive and tensile behaviour while utilising corresponding isotropic damage variables to capture the stiffness degradations in the compressive and tensile regimes. Material parameters are calibrated using uniaxially loaded concrete experiments. The results are compared with experimental and numerical data provided in the literature.
Shakor, P, Nejadi, S & Paul, G 1970, 'Effect of Elevated Temperatures as a Means of Curing in Inkjet 3D Printed Mortar Specimens', Biennial National Conference of the Concrete Institute of Australia, Concrete Institute of Australia, Sydney, Australia.
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Inkjet (Powder-based) three-dimensional printing (3DP) shows significant promise in concrete construction applications. The accuracy, speed, and capability to build complicated geometries are the most beneficial features of inkjet 3DP. Therefore, inkjet 3DP needs to be carefully studied and evaluated with construction goals in mind and employed in real-world applications, where it is most appropriate. This paper focuses on the important aspect of curing 3DP specimens. It discusses the enhanced mechanical properties of the mortar that are unlocked through a heat-curing process. Experiments have been conducted on cubic mortar samples that have been printed and cured in an oven at a range of different temperatures (e.g. 40, 60, 80, 90, 100°C). The results of the experimental tests have shown that 80°C is the optimum heat-curing temperature to achieve the highest compressive strength and flexural strength of the printed samples. These tests have been performed on two different dimensions of the cubic specimens 20x20x20mm, 50x50x50mm and on prism specimens with the dimensions of 160x40x40mm. The inkjet 3DP process and the post-processing curing are discussed. Additionally, 3D scanning of the printed specimens is employed and the surface roughness profiles of the 3DP specimens are presented.
Sirivivatnanon, V, Hocking, D, Cheney, K & Rocker, P 1970, 'Reliability of extending AS1141.60.1 and 60.2 test methods to determine ASR mitigation', Concrete 2019 app, 29th Biennial National Conference of the Concrete Institute of Australia, Concrete Institute of Australia, Sydney, Australia, pp. 1-8.
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The Australian Standards AS 1141.60.1 and AS 1141.60.2 were published in 2014 as Accelerated Mortar Bar Test (AMBT) and Concrete Prism Test (CPT) to determine the potential alkali-silica reactivity (ASR) of aggregates. Both methods were extended to evaluate the effectiveness of supplementary cementitious material (SCM) in mitigating ASR, similar to ASTM C1567 and CSA A23.2-14A, in a research program undertaken by the Cement, Concrete and Aggregates Australia (CCAA). Eight aggregates were tested with various dosages of either fly ash or slag and expansions measured up to 35 days and 2 years for AMBT and CPT respectively. In addition, the efficacy of SCMs to mitigate ASR was determined for four additional reactive aggregates based on the AMBT. The results were evaluated based on the corresponding reactivity criteria in the two Australian Standards. They showed that fly ash or slag can effectively be used to mitigate ASR and that the AMBT provided a more conservative dosage of SCM in mitigation ASR than the CPT. The required fly ash or slag dosages are also found to be consistent with recommendations given in HB79. Most importantly, there are findings from many exposure sites around the world that showed the reliability of AMBT and CPT in predicting the effectiveness of SCM-mitigated solution in long-term field-exposed large concrete blocks.
Sirivivatnanon, V, Moghaddam, F & Vessalas, K 1970, 'Effect of fineness and dosage of fly ash on selected properties of mortars', 29th Biennial National Conference of the Concrete Institute of Australia,, 29th Biennial National Conference of the Concrete Institute of Australia,, Concrete Institute of Australia, Sydney, Australia.
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In this paper, a laboratory investigation was carried out to evaluate the effect of fineness and levels of fly ash on the selected fresh, hardened and durability properties of mortars such as flow, compressive strength, drying shrinkage, strength activity index and alkali-silica reactivity. Portland cement was partially replaced by 20%, 30% and 40% of three kinds of fly ashes with different fineness (classified, run-of-station and ground run-of-station fly ashes). Fixed water to binder ratio of 0.40 and sand to binder ratio of 2.5 with a fixed dosage of water reducer were maintained for these mixes. In addition, some mixes containing classified and run-of-station fly ash with 50%, 60% and 70% cement replacement with fixed water to binder ratio of 0.55 and sand to binder ratio of 5 with a fixed dosage of water reducer were cast to evaluate the effect of fineness of fly ash in low strength mortar. Moreover, the effectiveness and required level of classified and run-of-station fly ash on mitigating alkali-silica reactivity are evaluated using accelerated mortar bar test method, and the results are reported in this paper. The results showed that all kinds of fly ashes improved the flowability of the mix with superior performance for the finer fly ash. X-ray diffraction and compressive strength test results demonstrated the effect of fineness of fly ash in decreasing the crystalline phase, increasing reactivity and improving the strength development. Drying shrinkage was decreased considerably with the inclusion of all kinds of fly ashes at all replacement levels. Incorporation of 25% classified and run-of-station fly ash is needed to control the expansion of mortar bars due to alkali-silica reactivity by the reducing the alkalinity of the mix.
Sirivivatnanon, V, Moghaddam, F & Vessalas, K 1970, 'Investigation on the influence of run of station fly ash in concrete pavement construction', 29th Biennial National Conference of the Concrete Institute of Australia, 29th Biennial National Conference of the Concrete Institute of Australia, Sydney, Australia.
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The achievement of sustainable development has been a major challenge facing the concrete industry for years. In recent years there have been changes, both technical and policy driven, that have the potential to affect the availability of classified fly ash. The possible shortage of classified fly ash (CFA) supply has prompted researchers at UTS to examine the possible use of run-of-station fly ash (RFA) for use in concrete applications. In this paper, an experimental study was carried out to evaluate the influence of partially replacing cement with 20% RFA on the heat of hydration, and microstructure of blended cement pastes compared to the paste containing 20% CFA. In addition, the effects of RFA on fresh and hardened concrete properties of pavement mixes were examined and compared to CFA concrete mix. Only two lots of RFA from one single source were examined, and hence the variability and effectiveness of RFA from other sources cannot be generalised. Properties critical to the use of fly ash in pavement concrete are examined according to the R83 specification.
Tang, Z & Li, W 1970, 'Rate-dependent behaviour of fly ash-slag geopolymer concrete with recycled aggregate', 13th International Conference on Shock and Impact Loads on Structures, SILOS 2019, pp. 413-420.
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Geopolymer concrete incorporating recycled aggregates is featured in prolonging the life cycle of construction materials and conserving the natural resource, coupled with embracing the sustainable binder-geopolymer. The aim of this study is to investigate the rate-dependent behaviour of geopolymer recycled aggregate concrete in comparison with that of geopolymer normal aggregate concrete. In this study, the recycled coarse aggregate (RCA), sourced from construction and demolition waste, was used as a full replacement for normal coarse aggregate (NCA) in geopolymer concrete. Additionally, ground granulated blast furnace slag (GGBFS), acting as a strength modifier, was used to substitute fly ash at the levels of 0%, 10%, 20%, and 30% of total binder. A 5000kN high-force servo-hydraulic test system was used for quasi-static compressive tests at a constant strain rate of 10-5 s-1, whereas dynamic compressive tests were carried out by using a Ø80-mm split Hopkinson pressure bar (SHPB) apparatus at strain rates ranging from 33 s-1 to 200 s-1. The compressive properties, including stress-strain curve, compressive strength, and failure mode, are obtained and analysed. The test results show that the compressive properties of geopolymer concrete exhibit strong strain rate sensitivity in terms of compressive strength and failure patterns. Although the RCA replacement worsened the quasi-static compressive strength of geopolymer concrete, it had insignificant effects on the compressive strength at high strain rates. Furthermore, the inclusion of slag could improve both the quasi-static and dynamic compressive strength.
Tapas, M, Vessalas, K, Thomas, P & Sirivivatnanon, V 1970, 'An AMBT Study on the Effect of Limestone on ASR Mitigation: Ground Limestone Vs. Interground Limestone in Cements', Proceedings of the International Conference on Sustainable Materials, Systems and Structures (SMSS2019) Durability, Monitoring and Repair of Structures, International Conference on Sustainable Materials, Systems and Structures, RILEM Publications S.A.R.L., Rovinj, Croatia, pp. 201-207.
Tapas, M, Vessalas, K, Thomas, P, Sirivivatnanon, V & Kidd, P 1970, 'Mechanistic Role of Supplementary Cementitious Materials (SCMs) in Alkali-Silica Reaction (ASR) Mitigation', Concrete in Practice-Progress Through Knowledge, Concrete in Practice-Progress Through Knowledge, Sydney, Australia.
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Alkali-silica reaction (ASR) can cause premature failure of concrete structures and therefore is a major concrete durability issue. The use of commonly available supplementary cementitious materials (SCMs) such as fly ash and slag is generally regarded as the most optimal and economical solution in mitigating ASR. However, the eminent closure of coal fired power stations in favour of greener technologies for producing energy and increasing demand in steel recycling threaten the future supply of SCMs that are currently available. Hence, the need to better understand the ASR mitigation process in order to be able to identify potential alternatives. This experimental study aims to provide a better understanding of ASR mitigation by studying the influence of various SCMs on ASR expansion, portlandite consumption and pore solution alkalinity. Results show that the efficacy of the SCMs in reducing ASR expansion can be correlated to their ability to consume portlandite and bind alkalis. Further, results suggest that any material that has high content of soluble Al2O3 and/or SiO2 is a potential SCM for ASR mitigation.
Thomas, P 1970, 'Application of Thermal Methods to the Characterisation of the States of Water in Precious Opal', CEEC-TAC5 & MEDICTA 2019, Central and Eastern European Committee for Thermal Analysis and Calorimetry and 14th Mediterranean Conference on Calorimetry and Thermal Analysis, Academica Greifswald, Rome, Italy, pp. 49-49.
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Precious opal is a hydrous silica (SiO2.nH2O) that is formed through a dissolution-precipitation process forming hydrated silicas with variable water content [1]. The gemmological value of precious opal is defined by its microstructure where the prized play-of-colour (POC) observed is a result of the diffraction of visible light from an ordered arrays of silica spheres. The monodispersed colloid of silica spheres are formed through an Ostwald type ripening process. Once the colloidal particles have grown to a suitable size for Bragg diffraction of visible light (ca. 200 to 400 nm in diameter; i.e. = 2dnsin where n is the refractive index of opal), aggregation occurs most likely through a homogeneous colloidal crystallisation process which results in the ordered array. Subsequently the array is solidified through precipitation of a second generation of silica which cements the array onto a solid coherent mineral specimen. The microstructure of the array can then be observed through the hydrofluoric etching of fresh fracture surfaces which reveal the ordered arrays of the monodispersed spherical particles. As the process of opal formation occurs in solution, a hydrous silica is formed. The silica network itself can be of an amorphous nature (opal-A) or is paracrystalline (opal-CT; cristobalite containing tridymite stacking faults) and contains water in the form of molecular and silanol (bound) water. The molecular water is trapped in cages, capillary pores and interstitial voids while the silanol water is present at the surface, internal interfaces (e.g. at capillary or void surfaces) and in the silica network as isolated broken bridges. The type and amount of each of these species of water is dependent on the environment in which opal formation occurs (e.g. temperature and pH) and hence water may be used as a probe to characterise the morphology structure of opal. Both thermal and spectroscopic methods have been used to successfully characterise the...
Thomas, P & Boyd-Weetman, B 1970, 'Aggregate reactivity to the alkali-silica reaction (ASR) in ground aggregate-cement pastes', CEEC-TAC5 & MEDICTA 2019, 5th Central and Eastern European Conference on Thermal Analysis and Calorimetry (CEEC-TAC5) and 14th Mediterranean Conference on Calorimetry and Thermal Analysis (Medicta2019), Academica Greifswald, Rome, Italy, pp. 185-185.
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A range of standard accelerated test methods for the screening of aggregates for susceptibility to the alkali-silica reaction (ASR) which causes deleterious cracking in concrete structures are available worldwide and two standard test have been recently adopted in Australia (AS 1141.60.1 (Accelerated mortar bar test (AMBT)) and AS 1141.60.2 (concrete prism test (CPT))). These accelerated test methods are empirical and based on expansion measurement correlated to field performance. The mechanism of deleterious ASR resulting in cracking involves two processes; the chemical processes involved in the formation of the expansive ASR gel and the mechanical action of the ASR gel of the concrete in crack formation. Expansion tests, although empirical in nature are important as they probe the mechanical potential of the reactivity of aggregates. The chemical processes involved in the phase development are also important as they provide the gel responsible for cracking and understanding these processes canlead to more effective methods of mitigation of ASR as well as alternative methods for the screening of aggregates for reactivity to ASR. This paper focusses on correlating reactivity of aggregates determined using the standard test methods with phase development in paste tests using ground aggregate-cement pastes aged under accelerated conditions. Two aggregates are investigated in this study, a micro-diorite (CPT non-reactive) and a greywacke (CPT reactive) which have been selected because of their relative reactivity to standard test methods. Both contain quartz as the phase potentially reactive to ASR. The aggregates were initially fine ground in a ring mill in order to make paste specimens using a general purpose Portland cement. Pastes specimens were prepared using a 3 to 1 aggregate to cement ratio with a water to cement ratio of 0.7. Pastes were initially hardened for 24 before stripping from the moulds and aging in alkali media (1 M NaOH) at elevated...
Thomas, P, Ha Hau, V, Vessalas, K, Sirivivatnanon, V & South, W 1970, 'Assessment of Aggregate Reactivity Using Slurry Tests', https://concrete2019.com.au/mobile/content.html, 29th Biennial National Conference of the Concrete Institute of Australia, Sydney.
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The testing and screening of aggregates for their alkali-silica reactivity (ASR) is generally carried out initially by petrographic analysis. If reactive aggregates are identified by petrographic analysis then a rapid screening of the aggregate’s potential to cause expansion using the accelerated mortar bar test (AMBT, AS-1141.60.1) is carried out to determine further reactivity potential. Aggregates that are found to be reactive in the AMBT method may be further screened using the concrete prism test (CPT, AS-1141.60.2). Both AMBT and CPT methods are a compromise between introducing accelerated and reactive conditions and monitoring the expansion over short and long periods of time but with conditions that are more closely aligned with field conditions. Given that these tests are empirical estimates of reactivity potential, alternate testing may be developed for the screening of aggregates. Alternate laboratory tests are rapidly carried out using slurry tests on small samples of ground aggregate (e.g. ASTM C289). Simulating storage temperatures used in the AMBT (80°C) and CPT (38°C) in 1 M NaOH (1.25% Na2Oe) is an alternate approach to the development of new rapid screening tests. To assess the degree of aggregate reactivity a co-reactant, calcium hydroxide (CH), may be added to the reaction mixture aiding reactivity assessment through the consumption of CH. The results of a laboratory trial into the reactivity of aggregates using a ground aggregate slurry test of this nature are reported in this paper. The results are correlated with standard test method data using AMBT and CPT (AS-1141.60.1 and 2) with a view to assessing this method (or methods of this type) as an alternative rapid screening approach in the identification of aggregate reactivity for ASR potential.
Thomas, P, Roboredo, C, Boyd-Weetman, B, Vessalas, K, Farah, D & Sirivivatnanon, V 1970, 'Investigation of ASR Reactivity through Slurry Dissolution Tests', 29th Biennial National Conference of the Concrete Institute of Australia, Sydney.
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The potential for alkali silica reaction (ASR) has been investigated through dissolution tests and the determination of the concentration of elemental species, Na, K, Ca and Si in the supernatant fluid of GP cement, aggregate and fly ash slurries. The aggregates selected for investigation were a reactive greywacke and a non-reactive micro-diorite both of which contain quartz. Alkali ions were delivered to the solution by the cement, although lower concentrations were released by both the aggregates and fly ash. Silica was released into solution according to aggregate reactivity. Rapid and local release of silica can yield an expansive ASR gel for reactive aggregate. Fly ash was observed to release silica rapidly indicating that the primary action of fly ash is through a competitive reaction for the formation of silica gel thus mitigating deleterious ASR. Quartz content as determined by X-ray diffraction analysis indicated that this phase was the main source of solution silica for the reactive aggregate.
Vu, TH, Gowripalan, N, De Silva, P, Kidd, P & Sirivivatnanon, V 1970, 'Carbonation and chloride induced steel corrosion related aspects in fly ash/slag based geopolymers - A critical review', FIB 2018 - Proceedings for the 2018 fib Congress: Better, Smarter, Stronger, International fib Congress, Fédération internationale du béton, Melbourne, Australia, pp. 3061-3076.
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Carbonation and the presence of chloride ions are considered as two important factors affecting steel reinforcement corrosion in conventional ordinary Portland cement (OPC) concrete. Particularly, large OPC pre-cast pipes and culverts are expected to have a longer design life due to lower water/cement ratios and higher cement contents (hence higher strength and lower porosity). Although most of the time they are buried underground and corrosion conditions may not be present, the aggressive nature of fluids (highly acidic or salty) they carry internally and the aggressive ground water in which they are located have resulted in deterioration of these elements due to corrosion of steel. Nowadays, attempts are made to replace OPC concrete pipes or culverts with fly ash/slag based geopolymer pipes and culverts. In this paper, a comparison of the corrosion aspects of reinforced concrete elements, particularly, pre-cast pipes and culverts, manufactured of OPC or blended cements and fly ash/slag based geopolymers is made. Carbonation rate in OPC concrete is different to that of geopolymer concrete mainly due to different pore structure and reaction products. The chloride ion penetration will also be different mainly due to different binding capacity, chemical products and pore structure. The threshold concentration of chloride ions required to initiate corrosion of steel reinforcement is also different. These aspects are critically reviewed which includes diffusion rates and cover requirements for long-term performance.
Vu, TH, Gowripalan, N, Sirivivatnanon, V, De Silva, P & Kidd, P 1970, 'Assessing Corrosion Resistance of Powder form of Geopolymer Concrete', 29 Biennial Conference of the Concrete Institute of Australia, Sydney Australia.
Wang, H, Li, Y, Zhang, G, Wang, J & Li, J 1970, 'Behaviours of lithium-based magnetorheological grease under triangular quasi-static test', Proceedings of 30th International Conference on Adaptive Structures and Technologies, ICAST 2019, pp. 131-132.
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This paper investigates the behaviour of lithium-based magnetorheological (MR) grease under the triangular quasi-static test. Three types of MR grease are prepared with weight fractions of carbon iron particles (CIP) as 30%, 50% and 70%, respectively. Quasi-static test of periodical triangular inputs, with various shear strain and strain rates, are employed to evaluate the performance of the MR greases, figure 1 and 2. Further evaluations are conducted by cross-checking the behaviour of the MR grease under various strain rate at a given max strain and the cases under various shear strains at a fixed strain rate.
Wei, J, Li, J & Wu, C 1970, 'Failure mechanisms of RC and UHPC columns under lateral impact', 13th International Conference on Shock and Impact Loads on Structures, SILOS 2019, pp. 449-457.
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Reinforced concrete (RC) columns are widely adopted in bridges, offices and car parks due to its low construction cost and easy formwork installation. Besides the service loads, RC column structures may experience accidental lateral impact loading during their service life, which could lead to structural failure. In this study, the impact response of axially loaded columns is investigated through low-velocity impact tests. Concrete materials adopted for column construction were ultra-high performance concrete (UHPC) and conventional concrete. The compressive strength for UHPC and conventional concrete were 136 MPa and 40 MPa, and the flexural strength for UHPC and conventional concrete were 21 MPa and 2.8 MPa, respectively. In total, 6 axially loaded columns, including 4 RC columns and 2 UHPC columns, were tested against 400 kg weight dropping from a height varying from 1 m to 1.5 m. UHPC columns outperformed the RC columns with marginal flexural damage. With the available material test data, a numerical model is built for RC and UHPC columns and validated against experimental testing results.
Xu, R & Fatahi, B 1970, 'Assessment of Soil Plasticity Effects on Seismic Response of Mid-Rise Buildings Resting on End-Bearing Pile Foundations', Springer International Publishing, pp. 146-159.
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Yu, Y, Li, Y, Li, J, Nguyen, TN, Li, S & Erkmen, E 1970, 'Vibration control of MRE isolator-embedded smart building using genetic algorithm', Proceedings of 30th International Conference on Adaptive Structures and Technologies, ICAST 2019, International Conference on Adaptive Structures and Technologies, Montreal, Canada, pp. 9-10.
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This study developed the adaptive genetic algorithm (GA) for vibration control of building structures subjected to ambient hazard excitations. An innovative smart building system was designed based on magnetorheological elastomer (MRE) isolators under each storey of the structure instead of being only installed beneath the entire structure. Such innovative system allows high authority semi-active control of storey responses by instantly changing the stiffness of the isolator, the control process of which can be considered as solving a global multi-objective optimization problem. Finally, a numerical investigation was conducted using a 5-storey international benchmark model under four benchmark earthquakes.
Yu, Y, Nguyen, TN, Li, J & Sirivivatnanon, V 1970, 'Soft computing techniques for evaluation of elastic modulus of ASR affected concrete', Concrete 2019, Concrete 2019, Sydney.
Yu, Y, Nguyen, TN, Li, J & Sirivivatnanon, V 1970, 'Soft computing techniques for evaluation of elastic modulus of ASR affected concrete', Concrete 2019: Concrete in Practice – Progress Through Knowledge, Concrete 2019: Concrete in Practice – Progress Through Knowledge, Sydney.
Zhang, X, Fatahi, B & Khabbaz, H 1970, 'Investigating Effects of Individual Fracture Length on Behaviour of Weak Rock Using Discrete Element Method', Proceedings of the 5th GeoChina International Conference 2018 – Civil Infrastructures Confronting Severe Weathers and Climate Changes: From Failure to Sustainability, GeoChina International Conference, Springer International Publishing, Wuhan, pp. 46-56.
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In this paper weak rock specimens with different individual fracture lengths are numerically simulated using the discrete element method (DEM). Effects of micro or macro-mechanical responses of intact and fractured specimens subjected to triaxial test have been studied. Various individual fracture lengths with a given fracture density within the weak rock specimens were reproduced using the particle flow code in three-dimension software (PFC3D). Different lengths of fractures were simulated by altering the size of each fracture to give insight over the influence of continual fractures and non-persistent fractures within bonded assemblies. As expected, for a given fracture density the individual fracture length affected the strength and deformability of rock mass. For an individual fracture length to specimen width ratio (the normalized fracture length) less than a limiting value, the effects of the individual fracture length on the stress-strain behaviour of rock specimens were more evident. Indeed, the strength decreased with decreasing the normalized fracture length. However, with a ratio above the limiting value, the effects of the individual fracture length were minimal. It can be concluded that for a given fracture density, present of shorter mini-fractures could be potentially more detrimental to stiffness and strength of the rock mass in comparison to longer major fractures.
Zhu, Q, Phung, MD & Ha, QP 1970, 'Crack detection using enhanced hierarchical convolutional neural networks', Australasian Conference on Robotics and Automation, ACRA, Australasian Conference on Robotics and Automation, ARAA, Adelaide, Australia, pp. 1-8.
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Unmanned aerial vehicles (UAV) are expected to replace human in hazardous tasks of surface inspection due to their flexibility in operating space and capability of collecting high quality visual data. In this study, we propose enhanced hierarchical convolutional neural networks (HCNN) to detect cracks from image data collected by UAVs. Unlike traditional HCNN, here a set of branch networks is utilised to reduce the obscuration in the down-sampling process. Moreover, the feature preserving blocks combine the current and previous terms from the convolutional blocks to provide input to the loss functions. As a result, the weights of resized images can be reduced to minimise the information loss. Experiments on images of different crack datasets have been carried out to demonstrate the effectiveness of proposed HCNN.