Alibeikloo, M, Khabbaz, H, Fatahi, B & Le, TM 2021, 'Reliability Assessment for Time-Dependent Behaviour of Soft Soils Considering Cross Correlation between Visco-Plastic Model Parameters', Reliability Engineering & System Safety, vol. 213, pp. 107680-107680.
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An elastic visco-plastic creep model was combined with the Monte-Carlo probabilistic method incorporating multivariate copula and nonlinear analysis to investigate the effects of uncertainties in the elastic visco-plastic model parameters on time-dependent settlement and the distribution of excess pore water pressure in soft soils under applied loads. The elastic-plastic model parameter (λ/V) and creep coefficient (ψ0/V) were considered as random variables with lognormal distribution while considering the cross correlation between these two random variables. When λ/V and ψ0/V were used as random variables, the coefficient of variation of time-dependent deformation gradually decreased approximately 25% over time until reaching an asymptote. By adopting over 50 years of monitoring data from the case study of Väsby test fill and results from the settlement ratio, the most appropriate cross correlation coefficient between selected random variables was introduced. The results revealed that increasing the cross correlation coefficient between λ/V and ψ0/V increased the standard deviation and the coefficient of variation of settlement up to 40%. Meanwhile, the corresponding statistical features for the predicted excess pore water pressure decreased as the cross correlation coefficient increased. This study also provides a practical insight into selecting the most suitable cross correlation coefficient between elastic visco-plastic model parameters, while adopting reliability-based design approach that captures the time-dependent deformation of embankments and structures built on soft soils.
Alqaisi, R, Le, TM & Khabbaz, H 2021, 'Combined effects of eggshell powder and hydrated lime on the properties of expansive soils', Australian Geomechanics Journal, vol. 56, no. 1, pp. 107-118.
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This study involves the utilization of eggshell powder (ESP) as a supplementary additive to lime stabilization of expansive soil and evaluates its potential in enhancing the performance of expansive soil treated with lime. Eggshell is a waste material obtained from several sources. Some of the challenges associated with dumping eggshell are odour, insect growth, disposal costs and availability of disposal sites. In order to reduce these environmental issues, eggshells can be processed into ESP and play a role as a soil stabilizing agent. Calcium oxide is considered to be the main ingredient of the ESP. Therefore, an experimental program is carried out to test a mixture of kaolinite, bentonite and Sydney fine sand, which is simulated to be as an artificial expansive soil. The eggshell powder was used as an additive to 5% lime in four percentages of 5%, 10%, 15% and 20% by total dry weight of the soil mass. Results of linear shrinkage, proctor compaction, and unconfined compressive strength tests after various curing time are presented in detail and compared with untreated soil samples. The outcomes of these experimental investigations indicated that the combination of eggshell powder and hydrated lime led to a further decrease in linear shrinkage and the maximum dry density of expansive soil samples. It was found that the improved geotechnical characteristics were more pronounced for 5% ESP treated expansive soil. At this percentage, the compressive strength at failure and the corresponding strain increased slightly by 18% and 9%, respectively, compared to the untreated expansive soil after 28 days of curing. Moreover, in comparison with lime (5%) only stabilized expansive soil, the combined lime (5%) and ESP (5%), induced approximately 15% build-up in the compressive strength of samples. Based on the reasonable laboratory test results, this addition is recommended to improve the shrinkage properties and stabilize the expansive soils where the high perfo...
Basack, S, Goswami, G & Nimbalkar, S 2021, 'Analytical and Numerical Solutions to Selected Research Problems in Geomechanics and Geohydraulics', WSEAS TRANSACTIONS ON APPLIED AND THEORETICAL MECHANICS, vol. 16, pp. 222-231.
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Geomechanical and geohydraulic engineering is a promising study area with several emerging research concerns. Most of such problems requires advanced level of mathematics to arrive at specific solutions. A wide range of approaches includes several analytical and numerical techniques for better understanding of such problems. In this paper, a few selected research problems are identified, and their solution techniques are demonstrated. The specific areas relevant to such problems are soil-structure interaction, ground improvement and groundwater hydraulics. This paper presents the problem identification, their mathematical solutions and results as well as pertinent analyses and useful interpretations to practice.
Basaglia, BM, Li, J, Shrestha, R & Crews, K 2021, 'Response Prediction to Walking-Induced Vibrations of a Long-Span Timber Floor', Journal of Structural Engineering, vol. 147, no. 2, pp. 1-15.
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Long-span timber floors are susceptible to annoying floor vibrations caused by human activities, which, in many cases, govern the timber floor design. Consequently, a reliable prediction of floor vibration responses under human activities, which relies on appropriate walking load models, can be crucial in the design to keep timber floors remaining competitive in the commercial building market. Much of the current design guidance for timber floor vibrations have been established from short-span floors in a residential context, and as a result, many designers refer to established design methods formulated for use with concrete and steel-framed buildings. These guidelines predict the floor response based on a deterministic single-person walking load model that differs depending on the classification of the floor as either a high- or low-frequency floor, which are assumed as a transient or resonant floor response, respectively. Recent advances in modeling human walking have been made, including a single footfall trace load that avoids the need to classify the floor, as well as load models that incorporate a probabilistic approach. To date, an investigation on different walking load models to predict the vibration response of long-span timber floors has not been undertaken, partially due to the fact that there are limited examples in practice. This paper presents the results of a recently completed state-of-the-art research project involving full-scale testing of long-span timber floors and the development of novel numerical models to investigate the applicability of the deterministic walking load model used in current floor vibration design guides, as well as two innovative single-person walking load models for predicting the floor responses of a single long-span timber cassette floor. The numerical investigation was carried out with a finite-element model calibrated with experimentally obtained modal properties. The comparison between the predicted respons...
Cao, D-F, Zhu, H-H, Guo, C-C, Wu, J-H & Fatahi, B 2021, 'Investigating the hydro-mechanical properties of calcareous sand foundations using distributed fiber optic sensing', Engineering Geology, vol. 295, pp. 106440-106440.
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Cao, J, Gowripalan, N, Sirivivatnanon, V & South, W 2021, 'Accelerated test for assessing the potential risk of alkali-silica reaction in concrete using an autoclave', Construction and Building Materials, vol. 271, pp. 121871-121871.
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To rapidly assess the potential risk of alkali-silica reaction (ASR) in concrete, an accelerated test using an autoclave by adopting multi-cycle 80 °C steam warming at atmospheric pressure is proposed. The influence of autoclave steam warming temperature, cycles/duration, and alkali dosage on expansion of mortar bars and concrete prisms was evaluated. Mechanical properties of concrete under accelerated ASR test were investigated. Furthermore, SEM-EDS analysis confirmed ASR products and indicated that the expansion is caused by ASR. The expansion limits considered for classifying aggregates were discussed. The experimental results demonstrated that the period required for assessing the potential risk of ASR in concrete (dacite aggregate in this study) can be shortened to 37 days.
Chen, Q, Peng, W, Yu, R, Tao, G & Nimbalkar, S 2021, 'Laboratory Investigation on Particle Breakage Characteristics of Calcareous Sands', Advances in Civil Engineering, vol. 2021, pp. 1-8.
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Many studies have demonstrated the fragility of calcareous sands even under small stresses. This bears an adverse influence on their engineering properties. A series of laboratory tests were carried out on poor-graded calcareous sands to investigate the crushability mechanism. Einav’s relative breakage and fractal dimension were used as the particle breakage indices. The results show that the particles broke into smaller fragments at the low-stress level by attrition which was caused by friction and slip between particles. In contrast, particles broke in the form of crushing at the relatively higher stresses. The evolution of the particle size was reflected by the variation in Einav’s relative breakage and fractal dimension. As testing commenced, the breakage index rapidly increased. When the stress was increased to 400 kPa, the rate of increase in the breakage index was retarded. As the stress was further increased beyond 800 kPa, the rate of increase in the fractal index became much smaller. This elucidated that the well-graded calcareous sands could resist crushing depending on the range of applied stresses. Based on the test findings, a new breakage law is proposed.
Chen, Q, Yu, R, Li, Y, Tao, G & Nimbalkar, S 2021, 'Cyclic stress-strain characteristics of calcareous sand improved by polyurethane foam adhesive', Transportation Geotechnics, vol. 31, pp. 100640-100640.
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Chen, Q, Yu, R, Tao, G, Zhang, J & Nimbalkar, S 2021, 'Shear behavior of polyurethane foam adhesive improved calcareous sand under large-scale triaxial test', Marine Georesources & Geotechnology, vol. 39, no. 12, pp. 1449-1458.
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Chen, Q-S, Peng, W, Tao, G-L & Nimbalkar, S 2021, 'Strength and Deformation Characteristics of Calcareous Sands Improved by PFA', KSCE Journal of Civil Engineering, vol. 25, no. 1, pp. 60-69.
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© 2020, Korean Society of Civil Engineers. Calcareous sand is widely distributed in the islands of the South China Sea, which could be promisingly used as the construction materials. However, particle breakage commonly occurs in calcareous sands, which may significantly influence their mechanical characteristics. To address these issues, an eco-friendly agent, i.e., polyurethane foam adhesive (PFA) is proposed to improve the engineering properties of calcareous sands, compared to the commonly used alkaline stabilizing agents (e.g., lime, cement). The objective of this work is to examine the effectiveness of using PFA in improving the strength-deformation properties of calcareous sand. A series of laboratory tests including direct shear tests, unconfined compression tests, and oedometer tests were performed on the calcareous sands improved by PFA. In addition, A scanning electron microscope (SEM) was conducted to reveal microstructural analysis of using PFA for calcareous sand. The experimental results provided insights into the shear strength, deformation modulus, as well as the micro-structural characteristics of improved calcareous sands with various PFA contents and particle size distributions.
Cowled, CJL, Crews, K & Gover, D 2021, 'Influence of loading protocol on the structural performance of timber-framed shear walls', Construction and Building Materials, vol. 288, pp. 123103-123103.
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Dang, CC, Dang, LC, Khabbaz, H & Sheng, D 2021, 'Numerical study on deformation characteristics of fibre-reinforced load-transfer platform and columns-supported embankments', Canadian Geotechnical Journal, vol. 58, no. 3, pp. 328-350.
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In this investigation, a ground-modification technique utilising a fibre-reinforced load-transfer platform (FRLTP) and columns-supported (CS) embankment constructed on multi-layered soft soils is proposed and investigated. After validating the proposed model with published data in the literature, numerical analysis was firstly conducted on the two-dimensional finite element model of a CS embankment without or with FRLTP to examine the influence of the FRLTP inclusion into the CS embankment system. Secondly, an extensive parametric study was performed to further investigate the effects of the FRLTP essential parameters — including platform thickness, shear strength, and tensile strength properties — and deformation modulus on the embankment performance during the construction and post-construction stages. Additionally, the influence of the embankment design parameters, such as column spacing, column length, and diameter, was examined. The numerical results reveal that the FRLTP inclusion can be effective in enhancing the CS embankment behaviour. It is also found that when increasing the platform thickness, the shear strength properties of FRLTP play a significant role in improving the overall performance of a column embankment with FRLTP.
Dang, LC, Khabbaz, H & Ni, B-J 2021, 'Improving engineering characteristics of expansive soils using industry waste as a sustainable application for reuse of bagasse ash', Transportation Geotechnics, vol. 31, pp. 100637-100637.
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Bagasse ash (BA) is an abundant industrial waste of the sugar-cane refining industry, and its improper disposal can result in a detrimental impact on the environment. In this investigation, BA is considered to assess the possible advantages of its pozzolanic component as a novel sustainable waste application for stabilisation of expansive soils. The engineering characteristics of expansive soils were investigated through an array of laboratory experiments on treated and untreated soil specimens mixed with various contents of additive and cured for different times. A comprehensive investigation of the microstructure evolution of soils after treatment was also undertaken using Fourier transform infrared and scanning electron microscopy techniques. The results revealed that addition of BA, lime, and in particular, combined BA-lime (BAL) remarkably improved the maximum strength (815%), the bearing capacity (9.2 times), the compressibility (83%), and the 100% swell properties of stabilised soils due to rich amorphous silica properties of BA waste that promoted higher pozzolanic reactivities of BAL-soil-mixtures and therefore, enhanced the engineering characteristics of treated soils. The findings showed that a proper combination of bagasse ash waste and lime, as a stabilising additive, can effectively enhance the engineering properties of expansive soil while addressing the environmental impact of BA waste disposal. The industrial waste (BA) can be reused as a cost-effective and green construction material for the benefit of sustainable development of civil infrastructure.
Doan, S & Fatahi, B 2021, 'Green’s function analytical solution for free strain consolidation of soft soil improved by stone columns subjected to time-dependent loading', Computers and Geotechnics, vol. 136, pp. 103941-103941.
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This paper proposes an analytical solution in terms of Green's function formulations for axisymmetric consolidation of a stone column improved soft soil deposit subjected to time-dependent loading under free strain condition. The mathematical derivations incorporate the pore water flows in radial and vertical directions in stone column and soft soil synchronously. The capabilities of the proposed analytical solution are evaluated via worked examples investigating the influences of three common time-dependent external surcharges (namely step, ramp and sinusoidal loadings) on consolidation response of the composite ground. The examples show that a faster increase of load from an initial surcharge to an expected loading might generate more significant excess pore water pressure to be dissipated during the early stages of consolidation, but the dissipation rate in soft soil would speed up significantly afterwards. The column and soil settlements along with the differential settlement between them also proceed faster corresponding to the acceleration of loading – unloading processes. Finally, the proposed analytical solution is employed to evaluate the excess pore water pressure dissipation rate at an investigation point in soft clay of a case history foundation. The calculation results exhibit a reasonable agreement with field measurement data when various constant values of stress concentration ratio are substituted into the solution to reflect the increase of stress concentration ratio with consolidation time in real practice.
Dong, W, Guo, Y, Sun, Z, Tao, Z & Li, W 2021, 'Development of piezoresistive cement-based sensor using recycled waste glass cullets coated with carbon nanotubes', Journal of Cleaner Production, vol. 314, pp. 127968-127968.
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Different from widely exploring the application of waste glass to replace natural aggregate or cement powder, this study firstly utilized waste glass cullets coated with carbon nanotubes (CNTs) as conductive fillers to develop novel self-sensing cement-based sensors. The coating efficiency of CNTs and self-sensing properties were also investigated in terms of workability, water absorption, mechanical properties, electrical resistivity and microstructure. The results show that CNTs are attached to the surfaces of waste glass particles, especially the small-size waste glass particles with high roughness. Workability decreased significantly with the increased waste glass. Cementitious mortar with sand replaced by CNTs-coated waste glass exhibited the highest flowability when the replacement ratio was 25%. Moreover, the water impermeability continuously increased with the content of waste glass. The compressive strength was higher than that of the control mortar, which reached the highest with 50% waste glass content. Additionally, an excellent piezoresistivity was achieved for cement-based sensors with CNTs-coated waste glass particles for the self-monitoring of stress magnitude and failure. The CNTs are uniformly distributed well in the cement matrix by attaching the surfaces of waste glass particles, thus the conductive passages are formed in cement-based sensors for structural health monitoring.
Dong, W, Li, W & Tao, Z 2021, 'A comprehensive review on performance of cementitious and geopolymeric concretes with recycled waste glass as powder, sand or cullet', Resources, Conservation and Recycling, vol. 172, pp. 105664-105664.
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Recycling waste glass for developing cementitious and geopolymeric concretes as sustainable construction materials have recently attracted increasing attentions for the construction industry. There are many previous studies on the effects of waste glass used as powder, sand or cullet based on the various sizes on the fresh and mechanical properties of concrete. However, there are few studies conducted on the durability performance of waste glass concrete. In this paper, in addition to a brief review on the fresh and mechanical properties and microstructure, the durability performance of concrete with waste glass is comprehensively reviewed under various environmental actions, including chemical attacks, chloride transport, high temperature, freeze-thaw cycles, carbonation, efflorescence, abrasion, alkali-silica reaction (ASR), and practical applications. It was found that the type, size and replacement ratio of waste glass significantly affect concrete durability. Compared to the glass cullet, the fine glass powder can usually improve the long-term durability, because the enhanced pozzolanic reactivity can reduce the ASR expansion due to the densified microstructure and reduced porosity. On the other hand, other factors such as mineral additives, mixing and curing methods also potentially affect the durability. Finally, some research perspectives and challenges of concrete with recycled waste glass are also presented and discussed. Considering the potential applications of waste glass concrete, this comprehensive review will provide an insight into an in-depth understanding of the production and performance for promising application.
Dong, W, Li, W, Shen, L, Zhang, S & Vessalas, K 2021, 'Integrated self-sensing and self-healing cementitious composite with microencapsulation of nano-carbon black and slaked lime', Materials Letters, vol. 282, pp. 128834-128834.
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In this paper, multifunctional cementitious composites with integrated self-sensing and self-healing properties are developed using microencapsulation of nano-carbon black (NCB) to enclose slaked lime (SL). The results show that the cracks healing efficiency is strongly improved with NCB enclosed SL. With SL, the self-sensing capacity of NCB-cementitious composite exhibits higher and more stable piezoresistivity before or after self-healing. The NCB enclosing SL particles not only achieve excellent piezoresistivity, but also preserve SL from initial hydration. Furthermore, the remained SL can be released for further reactions in the cracks. The results provide a promising integrated multifunctional self-sensing and self-healing cementitious composite for structural health monitoring application.
Dong, W, Li, W, Vessalas, K, He, X, Sun, Z & Sheng, D 2021, 'Piezoresistivity deterioration of smart graphene nanoplate/cement-based sensors subjected to sulphuric acid attack', Composites Communications, vol. 23, pp. 100563-100563.
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Smart cement-based sensors with self-sensing capacity have been explored for structural health monitoring (SHM) with the intrinsic piezoresistive performance. However, few studies had studied the piezoresistivity degradation of cement-based sensors after exposure to the aggressive environments, especially under sulphate acid attacks. In this study, graphene nanoplate (GNP)/cementitious composites were immersed in sulphuric acid solutions (concentrations of 0, 1%, 2%, and 3%) for 90 and 180 days. Then surface appearance, weight loss, mechanical properties, piezoresistivity and microstructure were investigated and compared before and after sulphuric acid immersion. The results show that after acid immersion, the surface deterioration and mass loss were increased, and the compressive strength was significantly decreased. As for the intact GNP/cementitious composite, the piezoresistivity exhibited excellent linearity and repeatability, demonstrating the great potential to act as intelligent cement-based sensors for SHM. After 90 and 180 days of acid immersion, the piezoresistivity was sensitive to the initial low load initially but then turned less sensitive to the later high load. The highly corroded GNP/cementitious composites exhibited porous microstructures associated with the low compressive strength. The fractional changes to resistivity (FCR) under the low load could be attributed to the compressed pores and voids filled with erosion products that would form conductive passages. In contrast, with the increase of applied load, the intact cement matrix became much denser, which in turn constrained the further development of conductive passages in the GNP/cementitious composites.
Dong, W, Li, W, Wang, K & Shah, SP 2021, 'Physicochemical and Piezoresistive properties of smart cementitious composites with graphene nanoplates and graphite plates', Construction and Building Materials, vol. 286, pp. 122943-122943.
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Graphene nanoplate (GNP) and graphite plate (GP) are promising functional nanofillers for smart self-sensing cementitious composites. The effects of GNP and GP on physicochemical, mechanical and piezoresistive properties of cementitious composite were investigated in this paper. The results show that cement hydration was accelerated with the increased amounts of GNP and GP because of nucleation effect. The electrical resistivity of GNP-cementitious composites was always lower than the counterpart with GP with the same concentration. On the other hand, percolation occurred for the GNP/cementitious composites at the dosages from 2 to 3% (by weight), while it never happens for the GP/cementitious composites. Moreover, the GNP/cementitious composites reached the maximum mechanical strength when the GNP content was 1.0%, while for the GP/cementitious composites, only minor strength improvement was obtained with a dosage of 0.5% GP. As for the piezoresistivity, the cementitious composites with GNP exhibited higher fractional changes of resistivity. Irreversible resistivity happened for 2–3% GP/cementitious composites subjected to cyclic compression, due to the poor and loose microstructures. The outcomes are expected to provide an insight into the application of GNP/cementitious and GP/cement composites as cement-based sensors for the future structural health monitoring.
Dong, W, Li, W, Zhu, X, Sheng, D & Shah, SP 2021, 'Multifunctional cementitious composites with integrated self-sensing and hydrophobic capacities toward smart structural health monitoring', Cement and Concrete Composites, vol. 118, pp. 103962-103962.
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In this study, multifunctional cementitious composites with integrated self-sensing and hydrophobicity capacities were developed and investigated using conductive graphene nanoplate (GNP) and silicone hydrophobic powder (SHP). The mechanical properties, permeability, water contact angle, microstructure and piezoresistivity were studied and compared under different contents of GNP and SHP. The highest compressive and flexural strengths with 1% SHP and 2% GNP reached 62.6 MPa and 8.9 MPa, respectively. The water absorption significantly was decreased with the content of SHP, but was minorly affected by GNP. The water contact angle firstly increased but then decreased with the dosages of GNP and SHP. SHP and GNP could reduce the microscale pores and enhance the density of microstructures. The piezoresistivity under compression firstly exhibited low gauge factor, but then gradually increased to a constant value under high-stress magnitude. Moreover, compared to the conventional cement-based sensors, this piezoresistive cementitious composites containing SHP and GNP as novel cement-based sensors are less sensitive to water content and humidity. The outcomes can provide an insight into promoting the application of multifunctional cement-based sensors toward structural health monitoring under various ambient conditions.
Fang, J, Wu, C, Rabczuk, T, Wu, C, Sun, G & Li, Q 2021, 'Correction to: Phase field fracture in elasto-plastic solids: a length-scale insensitive model for quasi-brittle materials', Computational Mechanics, vol. 67, no. 6, pp. 1769-1770.
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The original article contained typographical errors that a number of double brackets.
Far, H & Nejadi, S 2021, 'Experimental investigation on flexural behaviour of composite PVC encased macro-synthetic fibre reinforced concrete walls', Construction and Building Materials, vol. 273, pp. 121756-121756.
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Composite PVC encased concrete walls provide substantial advantages in terms of structural strength and durability enhancement, ultraviolet radiation and pest infestation resistance, design flexibility, ease of construction and excellent resistance to impact. In this study, the effects of using macro-synthetic fibre reinforced concrete on flexural behaviour of composite PVC encased walls in comparison with composite PVC encased walls filled with conventional plain concrete and reinforced concrete have been experimentally investigated. Fifteen composite PVC encased concrete wall specimens were cast and tested using three-point bending test. Based on the load-deflection curves resulting from the three-point bending tests, flexural parameters including ultimate loads, ultimate flexural strengths, stiffness and flexural rigidity values for cracked and uncracked conditions were determined for three different cases including i) test specimens filled with plain concrete, ii) test specimens filled with macro-synthetic fibre reinforced concrete, and iii) test specimens filled with reinforced concrete. The determined parameters as well as the measured load-deflection curves for the three cases were compared and the final findings have been discussed. Based on this study, it has become apparent that using BarChip 48 macro-synthetic fibre reinforced concrete in composite PVC encased walls instead of plain concrete can lead to 43.5% flexural strength improvement and 25% stiffness enhancement at the age of 28 days. Based on the experimental measurements and theoretical comparison in this study, it has been concluded that composite PVC encased walls filled with BarChip 48 macro-synthetic fibre reinforced concrete, without steel reinforcement, are deemed suitable for sway-prevented structures such as retaining walls. If using steel reinforcement in composite PVC encased retaining walls is not an option due to high-risk of steel corrosion in harsh environment; it is hig...
Far, H & Nejadi, S 2021, 'Experimental investigation on interface shear strength of composite PVC encased macro-synthetic fibre reinforced concrete walls', Structures, vol. 34, pp. 729-737.
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Over the past decade, Polyvinyl Chloride (PVC) stay-in-place formwork has become a popular alternative for conventional formwork in concrete construction industry due to its relatively lower cost of construction and ease of assembly. The PVC panels are joined using connectors and serve as a permanent formwork into which fresh concrete is poured to form composite PVC encased concrete walls. This study has experimentally investigated the effects of using macro-synthetic fibre reinforced concrete on the interface shear strength of composite PVC encased walls in comparison with composite PVC encased walls filled with conventional plain concrete and reinforced concrete. Nine composite PVC encased concrete wall specimens were cast and tested using direct shear tests. Based on the load–deflection curves obtained from the direct shear tests, the maximum shear loads and interface shear strength values were determined for three different cases including i) test specimens filled with plain concrete, ii) test specimens filled with macro-synthetic fibre reinforced concrete, and iii) test specimens filled with reinforced concrete. The determined parameters as well as the measured load–deflection curves for the three cases were compared and the final findings have been discussed. Based on the outcomes of this study, it has become apparent that the tested composite PVC encased macro-synthetic fibre reinforced concrete wall specimens can noticeably exhibit higher interface shear strength values compared to the tested wall specimens filled with plain concrete. Since AS 3600 (2018) does not prescribe the shear plane surface coefficients for determining the interface shear strength of composite PVC encased concrete walls, in order to enable structural designers to determine the interface shear strength for those panels using AS 3600 (2018), those coefficients have been extracted from the test results for the three mentioned cases and proposed for practical applications.
Far, H, Nejadi, S & Aghayarzadeh, M 2021, 'Experimental investigation on in‐plane lateral stiffness and degree of ductility of composite PVC reinforced concrete walls', Structural Concrete, vol. 22, no. 4, pp. 2126-2137.
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AbstractThis study investigates the in‐plane lateral stiffness and ductility of composite PVC encased concrete walls subject to the lateral loads using pushover tests to determine lateral strength and ductility characteristics of composite PVC encased walls filled with plain concrete, macro‐synthetic fiber reinforced concrete (RC), and steel RC. Eighteen concrete wall specimens were cast and subjected to pushover test to determine the load‐deflection curves. Based on the capacity curves resulting from the pushover tests, the yield and maximum displacements and subsequently structural ductility and performance factors according to Australian Standard for seismic design of buildings have been determined. The determined parameters as well as the initial and effective lateral stiffness values measured from the load‐deflection curves for all three cases were compared and the final findings have been discussed. Based on the outcomes of this study, it has become apparent that the tested composite PVC encased macro‐synthetic fiber RC walls can exhibit superior performance in terms of ductility when compared to the unreinforced concrete specimens. In addition, the results indicated that the initial in‐plane lateral stiffness values of the tested composite PVC encased macro‐synthetic fiber RC walls increased by 25% compared to the tested walls filled with plain concrete. In order to enable structural designers to design composite PVC encased concrete walls, ductility factors for this type of walls have been extracted from the test results for the three mentioned cases and proposed for practical applications. It has been concluded that all the PVC encased concrete walls evaluated in this study can be categorized as fully ductile structures.
Farooq, MA, Nimbalkar, S & Fatahi, B 2021, 'Three-dimensional finite element analyses of tyre derived aggregates in ballasted and ballastless tracks', Computers and Geotechnics, vol. 136, pp. 104220-104220.
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Scrap tyres are a significant source of pollution and pose a grave threat to the environment and human health. The present study aims to examine the application of Tyre Derived Aggregate (TDA) in a concrete slab track and ballasted track and compare its performance in both track forms. In this study, long-term performance of slab track and ballasted track subjected to train induced loading is demonstrated based on the three-dimensional finite element modelling. The most suitable constitutive hyperelastic model for TDA has been identified. Subsequently, the most suitable position for the location of TDA is determined for both track types. A comparative analysis between slab track and ballasted track, with and without TDA, is presented in terms of stress transfer, vibration reduction and displacement (elastic and plastic). It is shown that TDA helps in reducing up to 50% vibration levels of both track types. The influence of train speed and axle load on the vertical and horizontal displacement and stress response of both track forms is shown for a large number of load cycles. Overall, it is observed that the long-term performance of TDA is better in slab track compared to ballasted track.
Gao, C, Huang, L, Yan, L, Kasal, B, Li, W, Jin, R, Wang, Y, Li, Y & Deng, P 2021, 'Compressive performance of fiber reinforced polymer encased recycled concrete with nanoparticles', Journal of Materials Research and Technology, vol. 14, pp. 2727-2738.
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Nanomaterials have been used in improving the performance of construction materials due to their compacting micro-structure effect and accelerating cement hydration reaction. Considering the brittle characteristic of fiber reinforced polymer (termed as FRP) tube encased concrete and inferior properties of recycled concrete, nanoparticles were used in FRP tube encased recycled aggregate concrete. The axial compressive performance of FRP tube used in recycled concrete treated with nanoparticles strengthening, termed as FRP-NPRC, were investigated by axial compression experiments and theoretical analysis. Five experimental variables were considered including (1) the dosages and (2) varieties of nanoparticles (i.e. 1% and 2% of nanoSiO2, 1% and 2% of nanoCaCO3), (3) replacement ratios of recycled coarse aggregates (termed as RCAs) (0%, 50%, 70% and 100%) the RCAs were mainly produced from the waste cracked bricks, (4) the number of glass FRP (GFRP) tube layers (2, 4 and 6-layer) and (5) the mixing methods of concrete. Results indicate that the combination of FRP confinement and nanoparticle modification in recycled concrete exhibited up to 76.2% increase in compressive strength and 7.62 times ductility improvement. Furthermore, a design-oriented stress–strain model on the basis of the ultimate condition analysis were executed to evaluate the stress–strain property of this strengthened component.
Gao, K, Liu, Z, Wu, C, Li, J, Liu, K, Liu, Y & Li, S 2021, 'Effect of low gas concentration in underground return tunnels on characteristics of gas explosions', Process Safety and Environmental Protection, vol. 152, pp. 679-691.
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This study numerically investigated the effect of a very low gas concentration on a gas explosion's performance numerically using OpenFOAM. The use of the Harten–Lax–van Leer–Contact (HLLC) approximation algorithm based on the density-based solver was proposed to capture the shock wave. The process variable in XiFOAM of the OpenFOAM toolbox was used for the deflagration reaction. A gas explosion test was performed, and the numerical model with OpenFOAM was validated using the testing data. Based on the numerical investigation, the influence of a very low methane concentration on the flame and shock wave propagation law of a gas explosion was analyzed. It showed that the flame initially accelerated, followed by deceleration, and then accelerated again before slowing down. An increase in the methane concentration had an enhanced effect on the maximum overpressure ratio, which increased linearly with an increase in the methane concentration from 0 vol. % to 3.0 vol. % in the return tunnels. Increasing the explosive methane volume and concentration caused a significant increase in the flame spread distance. It was also noted that increasing the methane concentration caused a linear increase in the maximum overpressure ratio, and the methane volume and concentration both had a sensitive effects on the maximum overpressure ratio and average overpressure rising rate. The results clarified how the gas explosion law was affected by a very low gas concentration and provided theoretical support for controlling gas explosion disasters.
Ghosh, B, Fatahi, B, Khabbaz, H, Nguyen, HH & Kelly, R 2021, 'Field study and numerical modelling for a road embankment built on soft soil improved with concrete injected columns and geosynthetics reinforced platform', Geotextiles and Geomembranes, vol. 49, no. 3, pp. 804-824.
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He, X, Wang, F, Li, W & Sheng, D 2021, 'Efficient reliability analysis considering uncertainty in random field parameters: Trained neural networks as surrogate models', Computers and Geotechnics, vol. 136, pp. 104212-104212.
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This paper presents an efficient reliability analysis framework, by using trained artificial neural networks (ANNs) as surrogate models, for geotechnical problems where the random field parameters like the mean and standard deviation are themselves uncertain. Random field theory has been extensively used to model soil uncertainty and spatial variability. However, due to limited availability of data, random field parameters can rarely be estimated accurately, often estimated in confidence intervals (uncertain parameters). Monte Carlo based reliability analysis is computationally extremely demanding because the function to map outcomes of random fields to structural response can only be calculated via numerical simulations. The authors have used trained ANNs as surrogate models in reliability analysis. However, these ANNs are specific for random fields with deterministic parameters. This paper presents a new framework in which trained ANN models are for random fields with variable parameters. A key component is the design of experiments – generating representative outcomes. In the prediction of the bearing capacity for strip footings, the efficiency and accuracy of this framework are successfully demonstrated. This framework is also efficient in reliability sensitivity studies. One main finding is that ignoring random field parameter uncertainty could lead to underestimated failure probability and hence unsafe design.
Huang, L, Liu, Z, Wu, C & Liang, J 2021, 'Interaction between a tunnel and alluvial valley under plane SV waves of earthquakes by IBIEM', European Journal of Environmental and Civil Engineering, vol. 25, no. 12, pp. 2217-2235.
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© 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group. This paper investigates the dynamic interaction between a lined tunnel and an alluvial valley under plane SV waves with the indirect boundary integral equation method (IBIEM). The impact of different parameters on the displacement of sedimentary valley and the dynamic stress concentration factors (DSCF) of the lining inner and outer walls are studied. The dynamic response of a tunnel embedded in an alluvial valley is considerably different from that of a tunnel not embedded in an alluvial valley. Numerical results indicate that under the same frequency, different buried depths can change the distribution of displacement in the sedimentary area. The deeper the tunnel is buried, the more resonance points the response spectrum curve has. In general, the DSCF on the inner surfaces of the tunnels embedded in the sedimentary valley is obviously greater than that of the tunnels in the half space. However, the DSCF on the outer surfaces of the former is smaller than that of the latter. The results reported here will provide a quantitative basis to the security assessment and seismic design of lined tunnels.
Huang, S, Samali, B & Li, J 2021, 'Numerical and experimental investigations of a thermal break composite façade mullion under four-point bending', Journal of Building Engineering, vol. 34, pp. 101590-101590.
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© 2020 Elsevier Ltd This paper presents numerical and experimental investigations on a typical thermal break composite façade profile under four-point bending. The purpose of this study is to gain the knowledge of the interfacial behaviour between aluminum extrusion and polyamide insert beyond elastic range. Understanding the behaviour of this energy efficient façade profile within plastic range is important for the design under extreme loading, such as earthquakes, strong wind conditions and even blast loads. The experimental investigation was carried out on four types of beam specimens. The specimens were grouped by their span lengths with three specimens for each span length. As the specimens’ geometry and composite action are complicated, seven strain gauges were used per specimen including small strain gauges to fit in the limited space of the thermal break section. A three stage failure process was observed during the experiments. A numerical investigation was carried out by using Finite Element modelling to simulate behaviour of the thermal break composite façade profile under similar loading condition in order to compare with the testing results as well as to capture the corresponding failure mechanisms. Numerical simulations were setup by applying a proposed partitioned multi-phase failure model to simulate three stage failure process discovered by experiments. The results from FE models were compared and discussed with experimental counterparts. In summary, FE models showed consistent results to the experimental counterparts and it also provided the insight and more details of failure mechanism and stress distribution including interfacial condition details. Behaviour of the thermal break façade profile in the plastic range displayed excellent ductility and high strength capacity of this type of thermal break section in the plastic range after slip.
Jaradat, Y & Far, H 2021, 'Optimum stiffness values for impact element models to determine pounding forces between adjacent buildings', Structural Engineering and Mechanics, vol. 77, no. 2, pp. 293-304.
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Structural failure due to seismic pounding between two adjacent buildings is one of the major concerns in the context of structural damage. Pounding between adjacent structures is a commonly observed phenomenon during major earthquakes. When modelling the structural response, stiffness of impact spring elements is considered to be one of the most important parameters when the impact force during collision of adjacent buildings is calculated. Determining valid and realistic stiffness values is essential in numerical simulations of pounding forces between adjacent buildings in order to achieve reasonable results. Several impact model stiffness values have been presented by various researchers to simulate pounding forces between adjacent structures. These values were mathematically calculated or estimated. In this study, a linear spring impact element model is used to simulate the pounding forces between two adjacent structures. An experimental model reported in literature was adopted to investigate the effect of different impact element stiffness k on the force intensity and number of impacts simulated by Finite Element (FE) analysis. Several numerical analyses have been conducted using SAP2000 and the collected results were used for further mathematical evaluations. The results of this study concluded the major factors that may actualise the stiffness value for impact element models. The number of impacts and the maximum impact force were found to be the core concept for finding the optimal range of stiffness values. For the experimental model investigated, the range of optimal stiffness values has also been presented and discussed.
Jiang, S, Shen, L & Li, W 2021, 'An experimental study of aggregate shape effect on dynamic compressive behaviours of cementitious mortar', Construction and Building Materials, vol. 303, pp. 124443-124443.
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An experimental investigation is conducted to study the effect of aggregate shape on mortar dynamic failure behaviours. Split Hopkinson bar device is employed to compress cylindrical mortar samples containing irregular glass aggregates and rounded glass aggregates under high strain rates from 1000 s−1 to 2500 s−1. A new insight into the aggregate shape effect on the mortar cracking mechanisms is presented at the microscale using micro-CT. The cracking characteristics are found to be highly dependent on the aggregate shape, where more rounded aggregates in mortar are less likely to possess transgranular cracks after the initiation of intergranular cracks in the weak interfacial transition zone. These microscopic cracking mechanisms are validated by the cumulative distribution evolutions of particle size and morphological parameters (elongation and flatness), which are further manifested by the dynamic compressive strength. The results demonstrate that mortar with more regular aggregates exhibits higher dynamic compressive strength and strain rate sensitivity.
Kamali, S & Far, H 2021, 'Numerical Investigation on Shear Deflection of Steel Welded I Sections with Varying Span to Depth Ratios', International Journal of Steel Structures, vol. 21, no. 2, pp. 393-407.
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Deflection of the steel I-sections is an important phenomenon that needs to be taken into account to ensure that the serviceability limit state criteria of the Australian Standards are met. The method that is widely used to calculate the deflection of steel I-sections is by the use of existing formulae that only accommodate the bending stiffness of the beams. A numerical investigation is performed in this study to find the contribution of shear effects in the final deflection of the Welded-Beams (WB) and Welded-Columns (WC). The numerical analyses were carried out in SAP2000 and numerical model was first validated using the experimental results of welded plate girders. The model was then used to analyse simply supported WB and WC sections under uniformly distributed load (UDL) with varying span lengths. The results of the numerical analyses are reported in this study which compare the mid-span deflection values from the simply supported deflection formula with the numerical model deflection values. The data acquired from the numerical analyses were used to establish a span to depth ratio for WB and WC sections below which the shear deflection becomes significant. The analysis of the results obtained from the numerical investigation suggests that a predication error begins to emerge in the result that is acquired from flexure deflection formulae at a certain span-depth ratio.
Karki, D & Far, H 2021, 'State of the art on composite cold‐formed steel flooring systems', Steel Construction, vol. 14, no. 2, pp. 117-127.
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AbstractThis article presents a comprehensive review of the state of the art in composite cold‐formed steel flooring research over the past couple of years. The most relevant and significant literature references were reviewed to provide some insights into trends and developments in composite cold‐formed steel floors. Advantages of this type of composite flooring system are also highlighted. A broad description of mainly two types of composite floor – mainly consisting of cold‐formed steel and concrete, and cold‐formed steel and timber‐based floorboards – are outlined in this study. The experimental and numerical investigations that have been carried out worldwide are likewise discussed in the paper. The most important aspects covered are shear connection behaviour and the flexural and dynamic behaviour of the floors. There is also a brief description of fire testing.
Karki, D, Far, H & Saleh, A 2021, 'Numerical studies into factors affecting structural behaviour of composite cold-formed steel and timber flooring systems', Journal of Building Engineering, vol. 44, pp. 102692-102692.
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Lightweight flooring system made up of cold-formed steel joist, and timber floorboard is widespread but the benefits of composite action that arise due to the interaction of top flange of cold-formed steel joist and the bottom surface of timber floorboard as a result of mobilising the shear connection are not considered in their design. A three-dimensional (3D) finite element model was developed and validated against the experimental results for cold-formed steel and particle board flooring system. The validated numerical model was used for parametric studies to investigate the influence of various factors that affect the structural behaviour of the composite flooring system. The results from the parametric studies showed that higher strength and stiffness values of engineered timber product, as well as their increased thickness, enhances the moment capacity and stiffness of the flooring system. The reduction in the spacing of the cold-formed steel joist was found to increase the stiffness and hence the load-carrying capacity of the flooring system. The high strength to weight ratio of cold-formed steel flooring system is also demonstrated in this study. A simplified design method is proposed herein to predict flexural capacity of composite beams taking into account for the composite action. The finding in this study indicates that the design and construction of composite cold-formed steel and timber flooring system should be subjected to availability of the engineered timber product in the region,choice of timber floorboard thickness and joist spacing can be based on the ultimate strength and serviceability requirements of the flooring systems to make it cost-effective.
Leng, D, Zhu, Z, Xu, K, Li, Y & Liu, G 2021, 'Vibration control of jacket offshore platform through magnetorheological elastomer (MRE) based isolation system', Applied Ocean Research, vol. 114.
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Undesirable vibrations in offshore platforms due to ocean loadings may reduce platform productivity and increase the fatigue failure. This study proposes a magnetorheological elastomer (MRE) based isolation system to control the jacket platform oscillations and its effectiveness is numerically evaluated. The working principle and design method of MRE-based isolation system are proposed, and MRE materials with high magnetorheological effects are conceptually designed. Practical jacket offshore platforms are selected for case studies. Semi-active fuzzy controller (SFC) is utilized to achieve real-time non-resonance vibration control. The proposed fuzzy core is constructed conceptually by the dynamic analysis of object structure. Numerical results demonstrate that MRE isolation system with SFC significantly reduces the maximum, minimum and RMS of the deck displacement and acceleration under realistic irregular waves at different sea states. MRE system could also reduce the response spectrum peaks and present robustness under various deck's mass. The present study proves the feasibility of MRE isolation systems in the application of vibration control for marine structures.
Leng, D, Zhu, Z, Xu, K, Li, Y & Liu, G 2021, 'Vibration control of jacket offshore platform through magnetorheological elastomer (MRE) based isolation system', Applied Ocean Research, vol. 114, pp. 102779-102779.
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With high flexibility and low damping, offshore wind turbines (OWTs) are prone to external vibrations such as wind, wave and earthquake, either attacked individually or as combined loading cases. This study proposes a semi-active variable-stiffness tuned mass damper (VSTMD) with magnetorheological elastomer (MRE) materials to mitigate undesired dynamic responses of OWT. A jacket supported OWT with MRE-TMD installed at the top of the tower is adopted as an example to demonstrate the effectiveness of the proposed design under multiple hazards. A semi-active frequency tracing algorithm is proposed through which the current-dependent stiffness of MRE-TMD is controlled by tracking the acceleration of OWT tower. The numerical results demonstrate that the semi-active MRE-TMD can effectively attenuate the dynamic responses of OWT under multi-hazard loadings, and it outperforms the passive TMD in reducing the peak and RMS displacements of tower structure. Robustness analysis of semi-active MRE-TMD is also validated by considering OWT sudden loss of partial stiffness under multiple-loadings.
Li, H, Askari, M, Li, J, Li, Y & Yu, Y 2021, 'A novel structural seismic protection system with negative stiffness and controllable damping', Structural Control and Health Monitoring, vol. 28, no. 10.
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In this paper, an innovative controllable negative stiffness system (CNSS) integrating adaptive negative stiffness and controllable damping characteristics is proposed to realise desirable vibration protection and improve adaptability, hence being effective to various earthquakes. The force-displacement relationship of the CNSS is derived as the forward model to describe its nonlinear properties. Three representative control algorithms, i.e., Linear Quadratic Regular (LQR) control, H∞ control and Sliding Mode (SM) control, are utilised for the CNSS to attain optimal control force. Based on the Takagi-Sugeno-Kang (TSK) Fuzzy inference system optimised by Non-Dominated Sorted Genetic Algorithm II (NSGAII), a novel inverse model is proposed accordingly to obtain input current according to the required control force and real-time system responses. To demonstrate the feasibility and efficiency of the CNSS for structural seismic protection, a numerical case study is conducted on a three-storey building model with CNSS installed on its first floor. Four scaled benchmark earthquakes are employed as excitations for the case study. Ten evaluation criteria are adopted to assess and verify the performance of the CNSS, and comparisons are made with that of uncontrolled and passive controlled systems. The numerical results indicate that the proposed CNSS can significantly improve the vibration control performance on all evaluation criteria simultaneously in comparison with the other two conventional systems. In addition to having good suppression effects on peak floor displacement and peak inter-storey drift, the CNSS with the SM controller demonstrates superior performance on mitigating peak structure shear and peak acceleration response of the first floor.
Li, H, Yu, Y, Li, J & Li, Y 2021, 'Analysis and optimization of a typical quasi-zero stiffness vibration isolator', Smart Structures and Systems, vol. 27, no. 3, pp. 525-536.
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To isolate vibration at a low-frequency range and at the same time to provide sufficient loading support to the isolated structure impose a challenge in vibration isolation. Quasi-zero stiffness (QZS) vibration isolator, as a potential solution to the challenge, has been widely investigated due to its unique property of high-static & low-dynamic stiffness. This paper provides an in-depth analysis and potential optimization of a typical QZS vibration isolator to illustrate the complexity and importance of design optimization. By carefully examining the governing fundamentals of the QZS vibration isolator, a simplified approximation of force and stiffness relationship is derived to enable the characteristic analysis of the QZS vibration isolator. The explicit formulae of the amplitude-frequency response (AFR) and transmissibility of the QZS vibration isolator are obtained by employing the Harmonic Balance Method. The transmissibility curves under force excitation with different values of nonlinear coefficient, damping ratio, and amplitude of excitation are further investigated. As the result, an optimization of the structural parameter has been demonstrated using a comprehensive objective function with considering multiple dynamic characteristic parameters simultaneously. Finally, the genetic algorithm (GA) is adopted to minimise the objective function to obtain the optimal stiffness ratios under different conditions. General recommendations are provided and discussed in the end.
Li, M, Chen, Q, Wen, K, Nimbalkar, S & Dai, R 2021, 'Improved Vacuum Preloading Method Combined with Sand Sandwich Structure for Consolidation of Dredged Clay-Slurry Fill and Original Marine Soft Clay', International Journal of Geomechanics, vol. 21, no. 10, pp. 04021182-04021182.
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Li, P, Li, W, Sun, Z, Shen, L & Sheng, D 2021, 'Development of sustainable concrete incorporating seawater: A critical review on cement hydration, microstructure and mechanical strength', Cement and Concrete Composites, vol. 121, pp. 104100-104100.
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Many countries are experiencing freshwater crises due to the increasing growth of the population together with the infrastructure construction that is aligned with the needs of freshwater for concrete production. There are also deficiencies in freshwater in many coastal areas where seawater is more accessible. To reduce unnecessary resource-wasting and meanwhile drive sustainable development in the construction industry, great efforts have been made to utilize seawater as the alternative mixing water for concrete casting, which presents potential economical and environmental benefits in the coastal and island regions. This paper comprehensively reviews the current studies on the predominant performance differences between seawater-mixed and conventional concretes with freshwater. Particular attention is paid to the chloride-induced hydration mechanism due to the chloride ions in seawater. The main findings of this review reveal that although harmful ingredients in seawater may weaken some of the concrete performances, applying proper curing conditions and adding moderate additives and admixtures could significantly and effectively mitigate these defects in properties. However, the unstable chloride binding ability in cement hydrates cannot eliminate the risk of rebar corrosion caused by chlorides in seawater, resulting in a limited scope of practical application. Finally, some trade-offs are recommended in using seawater in concrete, suggesting prospects of applications in the future construction industry. This study guides for the safer use of seawater in sustainable concrete through reviewing the advanced research progress.
Li, W, Dong, W, Castel, A & Sheng, D 2021, 'Self-sensing cement-based sensors for structural health monitoring toward smart infrastructure', Journal and Proceedings of the Royal Society of New South Wales, vol. 154, pp. 24-32.
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Since its first appearance more than 100 years ago, concrete has had a significant impact on urban development — buildings, roads, bridges, ports, tunnels, railways and other structures. While traditional concrete is a structural material without any function, a new branch of concrete technology has produced smart (or intelligent) concrete, with superior self-sensing capabilities that can detect stress, strain, cracks and damage, and monitor temperature and humidity. With the incorporation of functional conductive fillers, traditional concrete can exhibit electrical conductivity with intrinsic piezoresistivity. This piezoresistivity means that the electrical resistivity of concrete is synchronously altered under applied load or environmental factors. The self-sensing electrical resistivity thus obtained can be an index or parameter to detect stress or strain changes in concrete, or cracks and damage to concrete. On the other hand, because of the relationship between electrical resistivity, temperature and humidity, self-sensing concrete can also monitor environmental factors. This smart self-sensing concrete can therefore be a promising alternative to conventional sensors for monitoring structural health and detecting traffic information from concrete roads, all of which are critical to achieving smart automation in concrete infrastructures.
Li, Z-X, Zhang, X, Shi, Y, Wu, C & Li, J 2021, 'Finite element modeling of FRP retrofitted RC column against blast loading', Composite Structures, vol. 263, pp. 113727-113727.
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Fiber-reinforced polymer (FRP) wrap could considerably improve the shear capacity and ductility of RC columns. FRP is therefore considered a potential material to strengthen the RC column against blast loading. Due to the high expense and safety concern of field blast tests, a very limited number of explosion tests on FRP retrofitted RC columns have been conducted, which hinders the understanding of the response of FRP retrofitted RC columns against blast loading. With advanced computational technology, it is convenient to develop a Finite Element (FE) model that can accurately capture the structural response of FRP retrofitted columns under blast loading. In this paper, a refined FE model was established to simulate the FRP retrofitted RC columns under blast loading. Strain rate effects on the concrete and steel reinforcing bar as well as the FRP composite of which the strain rate effect was commonly ignored, were all considered in the model. Comprehensive modifications were made to the Karagozian and Case concrete (KCC) model to accurately capture the mechanical properties of FRP-confined concrete. Finally, the FE model was validated with several available experimental tests. The developed FE model could capture the blast response of FRP retrofitted columns with good accuracy.
Li, Z-X, Zhang, X, Shi, Y, Wu, C & Li, J 2021, 'Predication of the residual axial load capacity of CFRP-strengthened RC column subjected to blast loading using artificial neural network', Engineering Structures, vol. 242, pp. 112519-112519.
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In this study, two genetic algorithm optimized backpropagation neural networks (GA-BPNN) were established to predict the ratio of residual axial load capacity to the maximum axial load capacity (referred to as RCI hereafter) of the non- and CFRP-strengthened RC columns based on a huge amount of simulation data. The first one can be used to predict the residual axial load capacity of the damaged non- and CFRP-strengthened RC columns induced by blast load with the input of several parameters including column dimensions, concrete strength, transverse reinforcement ratio, longitudinal reinforcement ratio, axial load ratio, CFRP stiffness, carbon fiber strength, peak pressure and impulse of the blast load. Therefore it can be used for the blast-resistant design of non- and CFRP-strengthened RC columns. The input variables of the second GA-BPNN were changed to be the ratio of residual mid-height deflection to the column height after the explosion, column dimensions, concrete strength, transverse reinforcement ratio, longitudinal reinforcement ratio, CFRP stiffness and carbon fiber strength. Since the input variables of the second GA-BPNN could be easily derived after the explosion, thus it could be used for the rapid damage assessment of RC columns. Damage assessments for three non- and CFRP-strengthened columns were also conducted using the first GA-BPNN.
Lin, X & Far, H 2021, 'Post-buckling Strength of Welded Steel I-Girders with Corrugated Webs', International Journal of Steel Structures, vol. 21, no. 3, pp. 850-860.
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Lin, X, Far, H & Zhang, X 2021, 'Shear Capacity Analysis of Welded Steel I-Girders with Corrugated Webs based on First Yield', International Journal of Steel Structures, vol. 21, no. 3, pp. 1053-1062.
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Ling, Y, Wang, K, Wang, X & Li, W 2021, 'Prediction of engineering properties of fly ash-based geopolymer using artificial neural networks', Neural Computing and Applications, vol. 33, no. 1, pp. 85-105.
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© 2019, Springer-Verlag London Ltd., part of Springer Nature. Fly ash-based geopolymer has been studied extensively in recent years due to its comparable properties to Portland cement and its environmental benefits. However, the uncertainty and complexity of design parameters, such as the SiO2/Na2O mole ratio in alkaline solution, the alkaline solution concentration in liquid phase, and the liquid-to-fly ash mass ratio (L/F), have made it very difficult to create a systematic approach for geopolymer mix design. These mix design parameters, along with fly ash properties and curing conditions (temperature and time), significantly influence key properties of the material, such as setting time and compressive strength. In this study, an artificial neural network (ANN) was used to develop models for predicting the key properties of high-calcium fly ash-based geopolymer according to its mix design parameters. The correlations between experimental measurements and ANN model predictions of setting time, compressive strength, and heat of geopolymerization were established based on the results of tests on 36, 273, and 72 geopolymer mixes, respectively. The results show that the correlations between the experimental measurements and ANN model predictions of the properties studied are all strong. ANN modeling was found to be a suitable computing method to analyze the effects of design parameters on geopolymer properties and showed that L/F exhibited the greatest effect on setting time, alkaline solution concentration had the greatest influence on compressive strength, and a mole ratio larger than 1.5 significantly impacted heat at the geopolymerization peak. The developed ANN models can be used as guidance for mix design of high-calcium fly ash geopolymer in engineering applications.
Liu, J, Wu, C, Li, J, Liu, Z, Xu, S, Liu, K, Su, Y, Fang, J & Chen, G 2021, 'Projectile impact resistance of fibre-reinforced geopolymer-based ultra-high performance concrete (G-UHPC)', Construction and Building Materials, vol. 290, pp. 123189-123189.
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This paper describes the mix design of geopolymer-based ultra-high performance concrete (G-UHPC) with the compressive strength from 100 to 150 MPa. Projectile impact tests at two striking velocities of ~550 m/s and ~800 m/s were then performed to explore the impact resistance of G-UHPC targets. G-UHPC without the addition of fibres yielded better impact resistance than Ordinary Portland Cement (OPC) concrete regarding crater damage and crack propagation, but inferior performance on reducing depth of penetration (DOP). The addition of fibres in G-UHPC effectively helped reduced DOP, crater damage and crack propagation. Steel fibres with a length of 10 mm and a volumetric fraction of 2% were most effective in resisting projectile impact compared with other G-UHPC specimens. To further comprehend the projectile impact performance of G-UHPC, a calibrated Karagozian and Case Concrete (KCC) model accounting for the strain rate effect was successfully used for G-UHPC in projectile analysis. Numerical results including single element and full-scale quasi-static tests, deceleration-time histories of projectiles during penetration and DOP of G-UHPC targets were obtained to validate the numerical models. After that, trendlines were regressed to predict DOP of G-UHPC at two striking velocities of ~550 m/s and ~800 m/s. Perforation limits of G-UHPC were also proposed for the design of both safe and cost-effective protective structures against projectile impact, in which the perforation limits of G-UHPC were taken as 1.1 times of DOP.
Liu, J, Wu, C, Liu, Z, Li, J, Xu, S, Liu, K, Su, Y & Chen, G 2021, 'Investigations on the response of ceramic ball aggregated and steel fibre reinforced geopolymer-based ultra-high performance concrete (G-UHPC) to projectile penetration', Composite Structures, vol. 255, pp. 112983-112983.
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This paper presents experimental and numerical studies on projectile impact resistance of ceramic ball aggregated and steel fibre reinforced geopolymer-based ultra-high performance concrete (G-UHPC) targets. Compared with plain G-UHPC, ceramic ball aggregated G-UHPC enhanced projectile impact resistance regarding crack propagation, crater damage and depth of penetration (DOP). A further improvement of projectile impact resistance was observed if a combined addition of steel fibres and ceramic balls was used. Numerical simulations were then performed to further comprehend the projectile impact on G-UHPC targets using the HJC constitutive model in the finite element software LS-DYNA. Numerically simulated DOP, projectile velocity and displacement histories were obtained and then validated through comparing with the existing models. The numerical perforation limits for 20 vol-% ceramic ball aggregated and 1.5 vol-% steel fibre reinforced G-UHPC were 240 mm at 568 m/s and 380 mm at 798 m/s, respectively.
Liu, K, Wu, C, Li, X, Liu, J, Tao, M, Fang, J & Xu, S 2021, 'The influences of cooling regimes on fire resistance of ultra-high performance concrete under static-dynamic coupled loads', Journal of Building Engineering, vol. 44, pp. 103336-103336.
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Liu, Z, Liu, J, Pei, Q, Yu, H, Li, C & Wu, C 2021, 'Seismic response of tunnel near fault fracture zone under incident SV waves', Underground Space, vol. 6, no. 6, pp. 695-708.
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This study investigated the impact of a non-causative fault on the dynamic response of a nearby lined tunnel under the incidence of plane SV waves using the indirect boundary element method. The effects of several critical parameters, such as the incident frequency, the inclination degree of the fault, the distance between the fault and the tunnel on the hoop stress of the lined inner and outer walls, were explored intensively. The numerical results indicated that the non-causative fault could significantly change the hoop stress distribution of inner and outer surfaces of the tunnels. In general, for the vertically incident seismic waves, when the tunnel was located in the foot wall (under the fault), the hoop stress within the tunnel was significantly greater than that of the tunnels in the non-fault half space, with an amplification factor of up to 117%. The amplification effect became more pronounced as the fault dip angle increased. However, when the tunnel was located in the hanging wall (above the fault), the non-causative fault could produce a significant shielding effect on the dynamic response of the tunnel under high frequency wave incidence, with the reduction of hoop stress being up to 81%. For low-frequency waves, though, the fault could lead to an increase of the hoop stress of the tunnel of up to 152%. The research results will provide a reference for the seismic design and safety protection of underground structures in non-causative fault sites.
Lu, Z-H, Wu, S-Y, Tang, Z, Zhao, Y-G & Li, W 2021, 'Effect of chloride-induced corrosion on the bond behaviors between steel strands and concrete', Materials and Structures, vol. 54, no. 3.
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The corrosion of steel strands due to the chloride contamination is one of the most common causes for the degradation of prestressed concrete infrastructure. In this paper, an experimental study was performed to investigate the bond behaviors between steel strands and concrete after suffered the chloride corrosion. Total twenty central and off-center pull-out specimens with different corrosion levels were prepared and tested, in which the electrochemical acceleration method was employed to induce various corrosion levels. The effects of corrosion rate, stirrup configuration and holding condition of concrete to the steel strands on the bond behaviors of steel strands were studied and compared, in terms of the failure mode, bond-slip relationship, bond strength, and bond toughness. The results show that both the ultimate bond strength and characteristic bond strength decreased with the increase of corrosion degree. The presence of stirrups can significantly enhance the bond performance, indicating the more ductile failure characteristic and increased bond toughness. Moreover, the prediction results using empirical and analytical models are also compared with the experimental results to verify their applicability and accuracies in predicting the bond strength of steel strands after corrosion.
Luo, J, Zhou, C, Li, W, Chen, S, Habibnejad Korayem, A & Duan, W 2021, 'Using graphene oxide to improve physical property and control ASR expansion of cement mortar', Construction and Building Materials, vol. 307, pp. 125006-125006.
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Alkali-silica reaction (ASR) is a slowly occurring reaction in concrete between alkaline pore solution and reactive non-crystalline silica in aggregates, which is a challenge to physical property and durability of concrete. The oxygen-containing functional groups coupled with large surface area of graphene oxide (GO) nanomaterial renders highly reactive interaction with cement-based composite. Here, the physical properties and ASR expansion test of cement mortars modified with varied loadings of GO (wGO) or/and Pyrex glass (GOPM) were implemented after optimizing GO dispersion efficiency in water. The water absorption and microstructures of GOPM were observed to figure out the mechanism of GO's effect on mechanical strength, permeability, and ASR expansion of GOPM. Results show, 15 kJ is the optimal sonication energy for the dispersion of 300 mL pristine GO-water suspension with 0.04% wGO; the effect of GO on improving the flexural and compressive strength of GOPM is remarkable, the maximal amplitude is up to 24.16%, 43.03% compared with the baseline, respectively; GO has great influence on long-term anti-permeability and controlling expansion, the nano-nucleation and interlocking effect of GO render the expansion rate of GOPM be well below 0.1% threshold.
Luo, Z, Li, W, Gan, Y, He, X, Castel, A & Sheng, D 2021, 'Nanoindentation on micromechanical properties and microstructure of geopolymer with nano-SiO2 and nano-TiO2', Cement and Concrete Composites, vol. 117, pp. 103883-103883.
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Fly ash-based geopolymers incorporated with 2% nano-SiO2 (NS)/nano-TiO2 (NT) particles were subjected to microstructural and statistical nanoindentation analysis. With the addition of both types of nanoparticles, the compressive strength of geopolymer and the micromechanical properties of N-A-S-H gel were increased. NS exhibited higher reinforcement effect than NT on macro-strength. However, NT more significantly enhanced gel micromechanical properties. NT and especially the NS were found to have a positive effect on the early reaction rate of geopolymer. After 28 days, the gel proportion obtained by Backscattered electron (BSE) images analysis was close values of 49.16%, 55.69% and 54.02% for reference sample and NS, NT reinforced geopolymer, which were more than two times of that from the statistical nanoindentation. The effects of NS and NT on microstructure, gel proportion and gel micromechanical properties were discussed to reveal the macro-strength reinforcement mechanism. The results obtained from different techniques were also compared and discussed.
Meng, Q, Wu, C, Li, J, Wu, P, Xu, S & Wang, Z 2021, 'A study of pressure characteristics of methane explosion in a 20 m buried tunnel and influence on structural behaviour of concrete elements', Engineering Failure Analysis, vol. 122, pp. 105273-105273.
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With increasing use of natural gas in urban metropolitan areas, utility tunnels that contain utility and gas lines have become critical infrastructure. A leak within a gas pipe may cause methane-air explosions in the tunnel, leading to structural damage and casualties. Thus, it is necessary to investigate the response of structural members against explosion loads in the tunnel. Few studies in the open literature have studied the effects of a methane-air explosion in a full-scale concrete tunnel. This study presents two 9.5% methane-air explosions in a tunnel with a dimension of 20000 mm × 1800 mm × 600 mm. The pressure characteristics are summarized and compared with existing pressure–time curve of the methane-air explosion in typical vented containers. Similarities of pressure characteristics between the current study and previous studies avaliable from the literature are identified. Apart from explosion pressure characteristics, concrete structural specimens with a dimension of 1800 mm × 400 mm × 90 mm are also investigated. Geopolymer concrete, ultra high performance concrete (UHPC) and conventional concrete with compressive strength of approximately 70 MPa, 150 MPa and 30 MPa, respectively, were used to manufacture the testing specimens subjected to the methane-air explosions in the tunnel. In this study, the cracks were observed on all specimens. Due to large size of the tunnel and gas leakage during blast, the pressure distribution in the tunnel is not as uniform as observed in methane-air explosion chamber from the previous literatures. The conventional concrete specimen positioned between two pressure sensors is selected to validate the numerical model in the present study. The calibrated numerical model is then used to study the structural responses of concrete specimen subjected to the captured pressure.
Metia, S, Nguyen, HAD & Ha, QP 2021, 'IoT-Enabled Wireless Sensor Networks for Air Pollution Monitoring with Extended Fractional-Order Kalman Filtering', Sensors, vol. 21, no. 16, pp. 5313-5313.
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This paper presents the development of high-performance wireless sensor networks for local monitoring of air pollution. The proposed system, enabled by the Internet of Things (IoT), is based on low-cost sensors collocated in a redundant configuration for collecting and transferring air quality data. Reliability and accuracy of the monitoring system are enhanced by using extended fractional-order Kalman filtering (EFKF) for data assimilation and recovery of the missing information. Its effectiveness is verified through monitoring particulate matters at a suburban site during the wildfire season 2019–2020 and the Coronavirus disease 2019 (COVID-19) lockdown period. The proposed approach is of interest to achieve microclimate responsiveness in a local area.
Nguyen, LV, Phung, MD & Ha, QP 2021, 'Iterative Learning Sliding Mode Control for UAV Trajectory Tracking', Electronics, vol. 10, no. 20, pp. 2474-2474.
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This paper presents a novel iterative learning sliding mode controller (ILSMC) that can be applied to the trajectory tracking of quadrotor unmanned aerial vehicles (UAVs) subject to model uncertainties and external disturbances. Here, the proposed ILSMC is integrated in the outer loop of a controlled system. The control development, conducted in the discrete-time domain, does not require a priori information of the disturbance bound as with conventional SMC techniques. It only involves an equivalent control term for the desired dynamics in the closed loop and an iterative learning term to drive the system state toward the sliding surface to maintain robust performance. By learning from previous iterations, the ILSMC can yield very accurate tracking performance when a sliding mode is induced without control chattering. The design is then applied to the attitude control of a 3DR Solo UAV with a built-in PID controller. The simulation results and experimental validation with real-time data demonstrate the advantages of the proposed control scheme over existing techniques.
Ottenhaus, L-M, Jockwer, R, van Drimmelen, D & Crews, K 2021, 'Designing timber connections for ductility – A review and discussion', Construction and Building Materials, vol. 304, pp. 124621-124621.
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Punetha, P, Nimbalkar, S & Khabbaz, H 2021, 'Simplified geotechnical rheological model for simulating viscoelasto‐plastic response of ballasted railway substructure', International Journal for Numerical and Analytical Methods in Geomechanics, vol. 45, no. 14, pp. 2019-2047.
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AbstractA proper understanding of the mechanical behaviour of the substructure layers is crucial for optimising the design and performance of a ballasted railway track. The recent advent of high‐speed trains and heavy haul freight wagons has heightened this need more than ever. The accurate prediction of the long‐term performance of the railway tracks under increased speed and loads still remains an intriguing challenge for researchers and design engineers. In this context, the present paper proposes a simplified geotechnical rheological model to evaluate the viscoelasto‐plastic response of the track substructure layers. The proposed approach combines plastic slider, elastic springs and viscous dampers to predict the transient response during a train passage, and the irrecoverable deformation accumulated in the track substructure over an operational period. The model simulates tri‐layered substructure (ballast, subballast, and subgrade) in comparison with existing rheological approaches employing either single or dual‐layered substructure. The model is validated against the field data published in the literature. An acceptable agreement between the predicted results and the field data verifies the accuracy of the model. Parametric investigations are conducted to study the influence of train and track parameters on the cumulative track deformation. The results demonstrate the enhanced capability of the rheological model to adequately capture the crucial effects of axle load, train speed and thickness of granular layers on the accumulation of track settlement. The proposed method can provide an effective tool for the practising engineers for quick prediction of changes to the geometry of railway tracks over their operational periods.
Qian, H, Li, J, Zong, Z, Wu, C & Pan, Y 2021, 'Behavior of precast segmental utility tunnel under ground surface Explosion: A numerical study', Tunnelling and Underground Space Technology, vol. 115, pp. 104071-104071.
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Over the past few decades, a large number of precast segmental utility tunnels have been constructed. Intensive research efforts have been devoted to understanding their performance under service and seismic loads. However, the vulnerability of precast segmental utility tunnels against accidental blast loads is seldom discussed. The present study performs a comprehensive numerical investigation on precast segmental utility tunnels against ground surface explosion. The numerical model is verified against testing data based on buried RC structures and semi-analytical equations in TM 5–855-1. Three types of precast tunnel connections are investigated, i.e., connection without shear keys, connection with trapezoid-shaped shear keys, and connection with wedge-shaped shear keys. The effects of detonation location and prestressing conditions are evaluated. The performances of precast segmental utility tunnels under low-level, medium-level and high-level threat explosions are obtained and compared with those of the conventional monolithic utility tunnel. Discussions on the dynamic responses and energy dissipation (ED) of different precast segmental utility tunnels are made. The influences of energy dissipating (ED) bar, shear link and burial depth on the dynamic responses of the precast segmental utility tunnel are also investigated numerically.
Qian, H, Zong, Z, Wu, C, Li, J & Gan, L 2021, 'Numerical study on the behavior of utility tunnel subjected to ground surface explosion', Thin-Walled Structures, vol. 161, pp. 107422-107422.
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Over the past few decades, underground utility tunnels have become increasingly popular in many countries, especially in North America and China. Utility tunnels host multiple services’ infrastructures inside an accessible underground space that allows regular inspection, maintenance, and easy replacement. Previous studies on the safety of underground utility tunnels were mainly focused on the seismic performances, their dynamic behaviors under accidental/hostile blast loads were seldomly investigated. TM 5-855-1 is frequently employed to calculate the ground shock load and responses of buried structures. However, it is only applicable for the cases with a scaled distance larger than 0.4 m/kg1/3. The present study performs a comprehensive numerical investigation on the blast performance of utility tunnel subjected to ground surface explosion with small scaled distance. With validated material and structural models, a FEM model based on a utility tunnel project is established. The influence of charge weight on blast resistance of the utility tunnel is studied numerically. The effect of the reinforcement ratio, shear reinforcement arrangement, buried depth and wall thickness are investigated under the scenario of a sedan car bomb overhead explosion. It is found that over 200 kg TNT ground surface explosion will cause a great threat to the utility tunnel with 2 m burial depth (scaled distance smaller than 0.4 m/kg1/3). The shear reinforcement arrangement is of great importance to the blast resistance of the utility tunnel. The failure mode of the roof can be changed from combined shear and flexural failure to flexural failure, with an increased reinforcement ratio. Increased wall thickness and buried depth can improve the blast resistance of the utility tunnel as expected. Safety buried depth, and wall thickness for a sedan car bomb overhead explosion are discussed in the present study.
Qu, F, Li, W, Tang, Z & Wang, K 2021, 'Property degradation of seawater sea sand cementitious mortar with GGBFS and glass fiber subjected to elevated temperatures', Journal of Materials Research and Technology, vol. 13, pp. 366-384.
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Effects of ground granulated blast-furnace slag (GGBFS) and glass fiber on the property degradation of seawater sea sand mortar (FSSM) after elevated temperature exposure were investigated in this study. The physical properties and mechanical strength of FSSM were compared with that of cementitious mortar prepared with demineralized water and river sand (FRRM). The results showed that when the mortars were exposed to normal temperature, the compressive strength of FSSM was higher than that of FRRM. GGBFS increased both the compressive and flexural strengths of FSSM, while glass fiber increased the flexural strength but slightly decreased the compressive strength. The maximum flexural strength of FSSM was achieved with 1 wt.% glass fiber and 30% GGBFS. After exposed to temperatures of 200 °C and 400 °C, the flexural and compressive strength losses of FSSM were lower than that of the corresponding FRRM, while the FSSM with glass fiber exhibited more compressive strength loss but less flexural strength loss compared to the FRRM. Additionally, GGBFS could densify the microstructure of FSSM, and decrease the losses of flexural and compressive strength after exposed to elevated temperatures. The calcium aluminosilicate hydrate (C–A–S–H) gels with higher ratios of Si/Ca and Al/Ca in the FSSM with GGBFS were significantly more stable at the temperature of 700 °C compared to the calcium silicate hydrate (C–S–H) gels with lower ratios of Si/Ca and Al/Ca in the FRRM or FSSM without GGBFS. Therefore, it can be included that the high temperature or fire resistance of FSSM can be improved by glass fibers and GGBFS.
Qu, F, Li, W, Wang, K, Tam, VWY & Zhang, S 2021, 'Effects of seawater and undesalted sea sand on the hydration products, mechanical properties and microstructures of cement mortar', Construction and Building Materials, vol. 310, pp. 125229-125229.
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Qu, F, Li, W, Wang, K, Zhang, S & Sheng, D 2021, 'Performance deterioration of fly ash/slag-based geopolymer composites subjected to coupled cyclic preloading and sulfuric acid attack', Journal of Cleaner Production, vol. 321, pp. 128942-128942.
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Coupled effects of cyclic preloading and sulfuric acid attacks on the performance deterioration of fly ash/ground granulated blast furnace slag (GGBFS) geopolymer mortar (GPM) were investigated in this study. Ordinary Portland cement mortar (OPM) was also prepared as the control for comparison. The testing parameters include visual appearance, mass change, compressive strength, degradation depth, microstructure and leaching behavior after exposure to sulfuric acid solutions. Before the exposure to sulfuric acid solutions, compressive strength of GPM was increased with the addition of GGBFS, but more strength reduction was caused by cyclic preloading compared to the OPM. On the other hand, after the exposure to different sulfuric acid attacks, GPM with higher content of GGBFS experienced server deterioration after preloading. Cyclic preloading probably caused microcracks or damages in mortars, thus increasing the probability of sulfuric acid deterioration. Although GPM exhibited more strength reduction due to preloading than the OPM, after 18-month exposure to sulfuric acid attacks, GPM with preloading still performed better than the corresponding OPM. Similarly, the corresponding GPM exhibited a lower mass loss and degradation depth compared to the OPM under the same conditions. This implies that the higher content of CaO in GGBFS and OPC increase the formations of ettringite and gypsum, which lead to more expansion and severer cracks and damages. Compared with the calcium silicate hydrate (C-S-H) gels in OPM, there are higher Al/Si ratios but lower Ca/Si ratios of cross-linked aluminosilicate polymer gels in GPM. Therefore, GPM exhibited less severe deterioration even with exposure to sulfuric acid attacks though.
Ramu, YK, Sirivivatnanon, V, Thomas, P, Dhandapani, Y & Vessalas, K 2021, 'Evaluating the impact of curing temperature in delayed ettringite formation using electrochemical impedance spectroscopy', Construction and Building Materials, vol. 282, pp. 122726-122726.
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Ramu, YK, Thomas, P, Sirivivatnanon, V, Vessalas, K, Baweja, D & Sleep, P 2021, 'Non-deleterious delayed ettringite formation in low alkali cement mortars exposed to high-temperature steam curing', Concrete in Australia, vol. 47, no. 1, pp. 32-38.
Rao, P, Wu, J, Chen, Q & Nimbalkar, S 2021, 'Three-dimensional assessment of cracked slopes with pore water pressure using limit analysis', Environmental Earth Sciences, vol. 80, no. 18.
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Rao, P, Wu, J, Jiang, G, Shi, Y, Chen, Q & Nimbalkar, S 2021, 'Seismic stability analysis for a two-stage slope', Geomechanics and Engineering, vol. 27, no. 2, pp. 189-196.
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This paper adopts the kinematic theorem of limit analysis to assess the seismic stability of a two-stage slope. The seismic effect is taken into account by using the pseudo-static approach. The failure mechanism for the slope is extended to include below-toe failure, toe failure and face failure. Validation of this approach is conducted by comparing the factor of safety with the data in the existing literatures. The stability charts are presented based on the graphical method for reading the factor of safety readily. Parametric study involving the effect of slope geometry, internal friction angle, seismic effect as well as depth coefficient on the stability of a two-stage slope is carried out. The critical failure surfaces with various parameters are plotted. The results obtained reveal the significant influence of slope geometry on the failure mechanism of a two-stage slope under static and seismic condition.
Rasouli, H & Fatahi, B 2021, 'Geosynthetics reinforced interposed layer to protect structures on deep foundations against strike-slip fault rupture', Geotextiles and Geomembranes, vol. 49, no. 3, pp. 722-736.
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In the present study, the interaction mechanism of a 10-story moment-resisting building frame sitting on the conventional piled raft foundation with a strike-slip fault rupture with a dip angle of 90̊ is studied via three-dimensional finite element numerical simulation using ABAQUS. In addition, an alternative composite foundation system with geosynthetics reinforced interposed layer between piles and raft is proposed to improve the safety and performance of foundation under strike-slip fault ruptures. The interposed layer is reinforced with two high tensile strength of the geotextile layer. The inelastic behaviour of piles under large ground deformations is simulated using moment-curvature relationships of the real reinforced concrete section of piles and ductility concepts. The performance of both composite and conventional piled raft foundations are evaluated in terms of the geotechnical and structural responses of foundations including rotational and translational displacements and shear forces of the raft, as well as shear forces and ductility capacity of piles. The obtained results show the superior performance of composite foundation with geotextile reinforced interposed layer in terms of a significant reduction in shear forces in the raft and piles, as well as ductility demand in the piles.
Sadeghi, F, Zhu, X, Li, J & Rashidi, M 2021, 'A Novel Slip Sensory System for Interfacial Condition Monitoring of Steel-Concrete Composite Bridges', Remote Sensing, vol. 13, no. 17, pp. 3377-3377.
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Steel-concrete composite (SCC) beams are widely employed in bridge decks. The interfacial shear transfer between the top concrete slab and the supporting steel beams significantly affects the overall load carrying capacity and performance of a bridge deck. The inaccessibility of the connection system makes the visual inspection difficult, and the traditional vibration-based methods are insensitive to this type of local damage. In this study, a novel interlayer slip monitoring system has been developed for interfacial condition assessment of SCC beams. The monitoring system is mainly based on the Ultra-flat Industrial Potentiometer Membrane (UIPM). The sensor film that is glued on a steel base is mounted on the concrete slab, and the wiper is installed on the steel beam. The interlayer slip between the concrete slab and steel beam is monitored by the relative displacement between the sensor film and the wiper. An experimental study has been carried out on a 6-m long composite bridge model in the laboratory. In the model, the concrete slab and the steel beams are bolt-connected, and the bolts could be loosened to simulate the defects in the shear connection system. Seven slip sensors are evenly installed along the bridge model. The sensors are calibrated using the testing machine before they are installed on the bridge model. Three damage scenarios are simulated by loosening bolts at different locations. Different loadings are also applied on the bridge to simulate the operational conditions. Undamaged and damaged scenarios have been considered within load increments, and data are collected and interpreted to find out how the slip changes. The results show that this system is reliable and efficient to monitor the interlayer slip for assessing the interface condition of composite structures.
Senanayake, S, Pradhan, B, Huete, A & Brennan, J 2021, 'Proposing an ecologically viable and economically sound farming system using a matrix-based geo-informatics approach', Science of The Total Environment, vol. 794, pp. 148788-148788.
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Healthy farming systems play a vital role in improving agricultural productivity and sustainable food production. The present study aimed to propose an efficient framework to evaluate ecologically viable and economically sound farming systems using a matrix-based analytic hierarchy process (AHP) and weighted linear combination method with geo-informatics tools. The proposed framework has been developed and tested in the Central Highlands of Sri Lanka. Results reveal that more than 50% of farming systems demonstrated moderate status in terms of ecological and economic aspects. However, two vulnerable farming systems on the western slopes of the Central Highlands, named WL1a and WM1a, were identified as very poor status. These farming systems should be a top priority for restoration planning and soil conservation to prevent further deterioration. Findings indicate that a combination of ecologically viable (nine indicators) and economical sound (four indicators) criteria are a practical method to scrutinize farming systems and decision making on soil conservation and sustainable land management. In addition, this research introduces a novel approach to delineate the farming systems based on agro-ecological regions and cropping areas using geo-informatics technology. This framework and methodology can be employed to evaluate the farming systems of other parts of the country and elsewhere to identify ecologically viable and economically sound farming systems concerning soil erosion hazards. The proposed approach addresses a new dimension of the decision-making process by evaluating the farming systems relating to soil erosion hazards and suggests introducing policies on priority-based planning for conservation with low-cost strategies for sustainable land management.
Shafaghat, A, Khabbaz, H & Fatahi, B 2021, 'Analytical and Numerical Approaches to Attain the Optimum Tapering Angle for Axially-Loaded Bored Piles in Sandy Soils', International Journal of Geomechanics, vol. 21, no. 7.
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This study aims to establish an equation to obtain the optimum tapering angle (αopt) for bored tapered piles that is correlated with pile geometry and sand properties that vary with the relative density. This αopt corresponds with the maximum axial bearing capacity when the volume of material in the tapered pile is maintained identical to the counterpart straight cylindrical pile. First, analytical formulations will be developed to estimate the axial bearing capacity of bored tapered piles that are embedded in sand. The proposed governing equations capture the shaft vertical bearing component of the tapered pile, which is unique to tapered piles and varies nonlinearly with the tapering angle (α). By differentiating the obtained bearing capacity equation for α, an αopt is achieved. The finite element method (FEM) will be adopted to conduct the numerical modeling and to calibrate the model parameters of the proposed analytical equation, which considers soil nonlinearities and interactions between the tapered pile and the surrounding soil that is subjected to axial loading. The UBCSAND constitutive model will be used to simulate the soil response near the tapered pile and the model parameters will be calibrated against laboratory test results for sandy soils with different relative densities. However, due to the complexity of the proposed differentiation and inverse calculation, a numerical solution will be used to obtain the results. Then, the load-displacement curves of the tapered piles will be attained numerically and αopt, which results in the maximum axial capacity of the pile, will be determined. The results exhibit good agreement between the analytically determined axial bearing capacity for the tapered pile and the corresponding numerical modeling predictions. Furthermore, a simplified empirical equation will be established to select αopt, which could be used by practicing engineers.
Sun, Y, Sumelka, W, Gao, Y & Nimbalkar, S 2021, 'Phenomenological fractional stress–dilatancy model for granular soil and soil-structure interface under monotonic and cyclic loads', Acta Geotechnica, vol. 16, no. 10, pp. 3115-3132.
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Tapas, MJ, Sofia, L, Vessalas, K, Thomas, P, Sirivivatnanon, V & Scrivener, K 2021, 'Efficacy of SCMs to mitigate ASR in systems with higher alkali contents assessed by pore solution method', Cement and Concrete Research, vol. 142, pp. 106353-106353.
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This study demonstrates the efficacy of supplementary cementitious materials (SCMs) to mitigate alkali-silica reaction (ASR) even when used in conjunction with cement of higher alkali contents (up to 1% Na2Oeq). The expansion of concrete prisms was studied immersed in simulated pore solution in order to address the limitations of conventional ASR testing methods, accelerated mortar bar test (AMBT) and concrete prism test (CPT). Expansion results demonstrate that 25% fly ash and 50% slag are both sufficient to mitigate ASR even with cements with alkali content up to 1% Na2Oeq and that the pore solution method is a viable alternative ASR testing method. Massive amounts of ASR products (~20 μm thickness) were observed in concretes without SCMs consistent with high degree of expansion and extensive cracking. Small amounts of ASR products (≤5 μm thickness) were also observed in concrete with SCMs despite absence of significant expansion.
Tapas, MJ, Vessalas, K, Thomas, P & Sirivivatnanon, V 2021, 'Influence of Limestone Mineral Addition in Cements on the Efficacy of SCMs in Mitigating Alkali-Silica Reaction Assessed by Accelerated Mortar Bar Test', Journal of Materials in Civil Engineering, vol. 33, no. 6, pp. 04021106-04021106.
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This study evaluates the effect of limestone mineral addition in cement on the efficacy of supplementary cementitious materials (SCMs) in mitigating alkali-silica reaction (ASR) using the accelerated mortar bar test (AMBT). Mortars with and without SCMs were prepared by substituting portions of 0% limestone general portland (GP) cement with increasing amounts of limestone. Mortars with SCMs (25% fly ash or 65% slag) exhibit negligible expansion regardless of the limestone content in the binder, whereas mortars without SCMs exhibit high and almost identical expansion for all limestone substitutions. The expansion results show that limestone does not aggravate ASR, has no detrimental effect on the efficacy of SCMs in ASR mitigation, and likewise has no observable ASR-mitigating properties under the test conditions. The calcium silicate hydrate (C-S-H) composition is not affected by the amount of limestone, which suggests that limestone has no influence on the alkali uptake in the C-S-H. This is supported by the pore solution analysis results where SCMs (both fly ash and slag) have drastically reduced the pore solution alkali concentration over time, whereas limestone substitution only resulted in an alkali reduction equivalent to the substitution (dilution). Moreover, the carboaluminate phases formed when limestone is present were observed to decompose under AMBT conditions; thus, their influence on ASR mitigation is not possible to discern from this study.
Tran, T & Ha, QP 2021, 'Semi-automatic control of network systems with non-monotonic Lyapunov function', International Journal of Control, vol. 94, no. 8, pp. 2144-2160.
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© 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group. A partially decentralised scheme for the semi-automatic control of network systems with stabilising agents is presented in this paper. The semi-automatic control of interconnected systems employing the stabilising agent whose installation is segregated from the associated control algorithm has been presented previously. In this development, the quadratic dissipativity constraint (QDC) associated with a non-negative supply rate is newly introduced for the stabilising agent. The closed-loop system having bounded disturbances is input-to-state stabilised with a non-monotonic Lyapunov function when the QDC is used with model predictive controllers. The effectiveness of the QDC for stabilising agents in the presented partially decentralised architecture is demonstrated via simulation studies of a frequency regulation problem in power systems.
Wang, H, Chang, T, Li, Y, Li, S, Zhang, G & Wang, J 2021, 'Field–Frequency-Dependent Non-linear Rheological Behavior of Magnetorheological Grease Under Large Amplitude Oscillatory Shear', Frontiers in Materials, vol. 8, pp. 1-17.
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This article investigates the influence of frequency on the field-dependent non-linear rheology of magnetorheological (MR) grease under large amplitude oscillatory shear (LAOS). First, the LAOS tests with different driving frequencies were conducted on MR grease at four magnetic fields, and the storage and loss moduli under the frequency of 0.1, 0.5, 1, and 5 Hz were compared to obtain an overall understanding of the frequency-dependent viscoelastic behavior of MR grease. Based on this, the three-dimensional (3D) Lissajous curves and decomposed stress curves under two typical frequencies were depicted to provide the non-linear elastic and viscous behavior. Finally, the elastic and viscous measures containing higher harmonics from Fourier transform (FT)-Chebyshev analysis were used to quantitatively interpret the influence of the frequency on the non-linear rheology of MR grease, namely, strain stiffening (softening) and shear thickening (thinning), under LAOS with different magnetic fields. It was found that, under the application of the magnetic field, the onset of the non-linear behavior of MR grease was frequency-dependent. However, when the shear strain amplitude increased in the post-yield region, the non-linear rheology of MRG-70 was not affected by the oscillatory frequency.
Wang, W, Wu, C, Yu, Y & Zeng, J-J 2021, 'Dynamic responses of hybrid FRP-concrete-steel double-skin tubular column (DSTC) under lateral impact', Structures, vol. 32, pp. 1115-1144.
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Hybrid fibre-reinforced polymer (FRP)-concrete-steel double-skin tubular column (DSTC) is a new form of composite column that consists of an outer FRP tube and an inner steel tube, with the space between them filled with concrete. Although many studies have been conducted on the hybrid DSTC, studies on its lateral impact behaviour are very limited. This study numerically investigates the dynamic responses of hybrid DSTC under lateral impact. Numerical models of the hybrid DSTCs were developed and validated with existing test results. Afterwards, the dynamic responses, including the deflection-time histories and the force–time histories, were analysed. Specifically, the bending moment and shear force distributions at typical cross sections were discussed, and the impact resistance (shear and flexure) from each component (FRP tube, concrete, and steel tube) was investigated. The results indicate that the hybrid DSTC exhibits ductile behaviour under lateral impact. Even though the FRP tube cannot contribute to the impact resistance directly, it can greatly improve the impact resistance of the concrete. Moreover, parametric analyses were conducted to investigate the influences of different parameters on the lateral impact resistance of hybrid DSTC. Finally, simplified design-oriented equations were developed to predict the dynamic flexural capacity of hybrid DSTC.
Wei, J, Li, J, Wu, C, Liu, Z-X & Fang, J 2021, 'Impact resistance of ultra-high performance concrete strengthened reinforced concrete beams', International Journal of Impact Engineering, vol. 158, pp. 104023-104023.
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To improve the impact resisting performance of reinforced concrete (RC) components, three strengthening designs based on ultra-high performance concrete (UHPC) are proposed in this study. Drop hammer impact test was conducted to evaluate the dynamic response and failure modes of RC beams and UHPC strengthened RC-UHPC beams. Test specimens included two control RC beams, a RC beam with UHPC layer retrofitted on the tension surface, a RC beam with UHPC layers retrofitted on both the compression and tension sides, two RC beams with UHPC layer that was not directly attached to the tension surface, but with 5 mm gap between the interfaces. Test results showed UHPC strengthened beams had a good impact resistance. Under the impact from 641 kg weight dropping from 0.5 m, with a 15 mm UHPC layer directly attached to the tension surface of the RC beam, the crack pattern shifted from concrete spalling to diagonal shear failure, and the maximum and residual displacements decreased by 9.1% and 25.3%, respectively. RC-UHPC beams with non-attached interfaces exhibited even better impact resistance, the UHPC layer was able to develop multiple energy dissipating tensile cracks prior to failure, and the gap ensured a larger moment resistance leading to reduced beam deflections. The repeated impacts were performed on RC-UHPC beams. With the same total impact energy, the single impact was found to be more hazardous than the repeated impacts. Nonlinear finite element modelling was developed to further interpret the experimental results. With the validated numerical model, energy absorption curves, dynamic shear force and bending moment distribution diagrams were derived. Based on the experimental and numerical data, the shear mechanisms of RC beams and RC-UHPC beams were studied. The effects of non-attached spacing length, spacing depth and UHPC layer thickness were investigated in the parametric study.
Wei, J, Li, J, Wu, C, Liu, Z-X & Li, J 2021, 'Corrigendum to “Hybrid fibre reinforced ultra-high performance concrete beams under static and impact loads” [Eng. Struct. 245 (2021) 112921]', Engineering Structures, vol. 247, pp. 113236-113236.
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The authors regret, in the article “Hybrid fibre reinforced ultra-high performance concrete beams under static and impact loads” published in ENG STRUCT. 2021; 245, in Section 3.2.3, the content “vi. Determine the crack opening distance, ω (i.e. Eq. (9)-(10)). Match the analytical value and the value from step (i) by adjusting the length of the crack, αde, and repeating from step (ii).” and the Eqs. (9) and (10) should be omitted. Rather than the described step “vi” and the Eqs. (9) and (10), the relationship between the crack length αde and crack opening distance ω was determined based on experimental results presented in the paper. The relationship between mid-span displacement and CMOD could be obtained from Fig. 6. The mid-span deflection Δt is equated to the sum of the central elastic deflection Δe and the additional deflection due to cracking Δc: [Formula presented] Before cracking, the central elastic deflection Δe is expressed as follow: [Formula presented] The plane rotation of the prism is [Formula presented] The experimental Δtversus CMOD relationship could be transferred to αde versus ω relationship: [Formula presented] [Formula presented] The omitted information does not impact the analytical results or the scientific conclusions of the article in any way. The authors would like to apologise for any inconvenience caused.
Wei, J, Li, J, Wu, C, Liu, Z-X & Li, J 2021, 'Hybrid fibre reinforced ultra-high performance concrete beams under static and impact loads', Engineering Structures, vol. 245, pp. 112921-112921.
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High mechanical strength and ductility of fibre reinforced ultra-high performance concrete (UHPC) are beneficial to its loading capacity under static and dynamic loads. To further improve the material performance, especially the crack restraint capability and flexural capacity, hybrid fibre reinforcement in UHPC is investigated in the present study. This study first investigated the influence of hybrid straight steel fibres on the static mechanical performance of UHPC. Four mixtures with single and hybrid fibre reinforcement were developed. Fibres with three different lengths (6, 10, 15 mm) but identical diameter (0.2 mm) and volume dosage (2.5%) were incorporated. Quasi-static compression and flexural tests were conducted on these mixtures. The findings in this study indicated that while longer fibre provided an improvement of both compressive strength and elastic modulus, UHPC with hybrid fibres demonstrated better flexural performance. With notched three-point bending test results, tensile softening curves and fracture energy of UHPC were obtained and discussed. The flexural strength and fracture energy of mixture with hybrid long and short fibre was 21.84% and 20.13% greater than those with single long fibre reinforcement. Subsequently, the dynamic behaviour of UHPC beams (2000 × 168 × 168 mm) with a single and hybrid fibre reinforcement was investigated against low-velocity impact. The impact scenario was modelled with 641 kg drop hammer falling freely to the mid-span of the UHPC beams. The test results showed all specimens exhibited flexural response with minimal damage. The impact resistance of UHPC beams reinforced with hybrid fibres was found better than that with single long fibre reinforcement. The maximum and residual displacement of the mixture with hybrid long and medium fibre was 16.08% and 23.95% lower than that with long fibre reinforcement.
Xiao, H, He, L, Li, X, Zhang, Q & Li, W 2021, 'Texture synthesis: A novel method for generating digital models with heterogeneous diversity of rock materials and its CGM verification', Computers and Geotechnics, vol. 130, pp. 103895-103895.
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The interaction of meso-structures determines the macro-mechanical properties of rock material. Therefore, reliable description of heterogeneous diversity in rock is of great significance for studying its mechanical response and fracturing process. Based on the Markov random field theory, the texture synthesis method is optimized in terms of input exemplar and its best matching neighborhood size by using the mean shift clustering algorithm and the color histogram statistics. The optimized method can generate many parallel images of rock materials which have the function of feature replication and the characteristics of diverse heterogeneity. The reliability of the heterogeneous diversity models generated by the texture synthesis method is verified from three fundamental levels, including the CIELab color space, the geometric parameters of particles, and the numerical mechanical properties (CGM). The stress–strain curves and damage evolution processes of synthetic digital models under uniaxial compression have a strong characterization ability. Therefore, this new digital modeling method that represents the structural details and heterogeneous diversity of rock material can be utilized for evaluating the composition similarity and heterogeneous geometric features, and provide abundant materials for subsequent numerical mechanical analysis. This method provides a new idea for studying the meso-mechanical properties and failure mechanism of rock materials.
Xu, S, Liu, Z, Li, J, Yang, Y & Wu, C 2021, 'Dynamic behaviors of reinforced NSC and UHPC columns protected by aluminum foam layer against low-velocity impact', Journal of Building Engineering, vol. 34, pp. 101910-101910.
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© 2020 Elsevier Ltd Two strategies were proposed in this study to improve the safety of RC columns under low-velocity impact loading. One is setting up the protective closed-cell aluminum foam (CCAF) layer on the surfaces of RC columns for general structures, and the other one is utilizing the combination of the CCAF layer and UHPC for important structures. For verifying the effectiveness of these two strategies, both experimental and numerical investigations on the dynamic behaviors of reinforced normal strength concrete (R–NSC) and ultra-high-performance concrete (R–UHPC) columns protected by the CCAF layer against low-velocity impact were presented in this study. Two R–NSC columns and two R–UHPC columns were tested by the free-falling drop-weight system. The failure modes, failure process, time history of impact force and deflection were discussed in detail. Moreover, a 3D finite element model was developed to further investigate the impact dynamic behaviors of R–NSC columns and R–UHPC columns protected by the CCAF layer. The test results demonstrated that the CCAF layer can protect both R–NSC columns and R–UHPC columns effectively by reducing the impact force and absorbing a large amount of impact energy. Correspondingly, the safety of RC columns was also effectively improved since the impact force between the target and the impactor was reduced significantly by the adoption of the aluminum foam layer, and it verified strategy one. Furthermore, R–UHPC columns showed a better impact-resistant performance than R–NSC columns, especially, R–UHPC columns with the CCAF layer showed superior impact-resistant performance, and it verified strategy two. The finite element model can predict the dynamic behaviors of aluminum foam protecting R–NSC and R–UHPC columns with reasonable accuracy. Eventually, the energy absorption of the specimens was investigated by the numerical model.
Xu, S, Wu, P, Liu, Z & Wu, C 2021, 'Calibration of CSCM model for numerical modeling of UHPCFTWST columns against monotonic lateral loading', Engineering Structures, vol. 240, pp. 112396-112396.
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The objective of this study is to calibrate continuous surface cap model (CSCM) for ultra-high-performance concrete (UHPC), and then to investigate the structural behavior of UHPC filled thin-walled steel tubular (UHPCFTWST) column against monotonic lateral loading via numerical simulation of nonlinear pushover analysis. The parameters of CSCM model for UHPC were derived via fitting experimental data of a series of tests on UHPC under uniaxial/triaxial states. Subsequently, a detailed 3D FE (finite element) model of UHPCFTWST column against monotonic lateral loading was developed and validated. After that, the effect of main design parameters, including steel ratio, steel grade, axial compression ratio, dosage of steel fiber, and bonding strength, on the structural behavior of UHPCFTWST column against monotonic lateral loading was investigated via a parametric study based on the FE model. Eventually, the axial pressure-moment (P-M) interaction diagram of a specified UHPCFTWST column was derived to illustrate the sectional response. Comparisons of the lateral behavior of UHPCFTWST column with that of normal strength concrete (NSC) filled steel tubular (NSCFST) column were also made for better illustrations. It indicates that the lateral load capacity and ductility were both improved with the increase of steel ratio, whereas the increase of steel grade improved the lateral load capacity but reduced the ductility owing to the increase of yield drift ratio. Moreover, the increase of axial compression ratio improved the lateral load capacity but significantly degraded the ductility. Although the increase of the dosage of steel fiber improved the lateral load capacity and ductility, but a suitable volume ratio should be specified in consideration of the cost. The comparisons with NSCFST column indicated the advantage and potential of UHPC application to concrete filled steel tubular (CFST) column with a thinner steel tube and a higher grade of steel. The P-M ...
Xu, S, Yuan, P, Liu, J, Pan, Z, Liu, Z, Su, Y, Li, J & Wu, C 2021, 'Development and preliminary mix design of ultra-high-performance concrete based on geopolymer', Construction and Building Materials, vol. 308, pp. 125110-125110.
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This study reports a preliminary mix design of the geopolymer-based ultra-high-performance concrete (G-UHPC) developed using the alkaline activated alumino-silicate source materials. A combination of the sodium silicate (Na2SiO3) solution and sodium hydroxide (NaOH) was used as the alkaline activator, and the alumino-silicate source materials included the granulated blast furnace slag (GGBFS), fly ash and silica fume. The effect of the sodium silicate modulus, fly ash, GGBFS, Si/Al ratio, Ca/(Si + Al) ratio and steel fiber on the flowability of the fresh mixture and mechanical behavior of G-UHPC was comprehensively investigated via a series of flowability, compression and flexure tests. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were conducted to reveal the performance enhancement mechanism based on the reaction products and micromorphology. It was observed that an increase in the sodium silicate modulus, GGBFS and Si/Al ratio negatively impacted the flowability of the fresh G-UHPC mixture, whereas a significantly positive effect on the flowability was observed on incorporating the fly ash. Overall, the compressive and flexural strength of G-UHPC exhibited an increasing trend, followed by a decline, on increasing the sodium silicate modulus, fly ash, GGBFS and Ca/(Si + Al) fractions. The compressive and flexural strength demonstrated an identical trend on increasing the Si/Al fraction at a CaO fraction of 0.1 or 0.2. On the other hand, an increment in the Si/Al fraction exhibited a negative impact on the compressive and flexural strength as the CaO fraction increased to 0.3. The steel fiber dosage negatively affected the flowability, whereas an increase in the steel fiber dosage enhanced the compressive and flexural strength. Further, the flowability and flexural strength could be effectively estimated from the length (Lf) -to-dimeter (Df) ratio (Lf / Df), whereas 1/(LfDf)could be used to estimate the compressive strengt...
Xu, T, Li, Y, Lai, T & Zheng, J 2021, 'A simplified design method of tuned inerter damper for damped civil structures: Theory, validation, and application', Structural Control and Health Monitoring, vol. 28, no. 9.
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Xu, Z, Li, J, Wu, P & Wu, C 2021, 'Experimental investigation of triaxial strength of ultra-high performance concrete after exposure to elevated temperature', Construction and Building Materials, vol. 295, pp. 123689-123689.
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Equipped with excellent strength and energy absorption capacity, ultra-high performance concrete (UHPC) is a promising material to improve structural resistance against extreme loads. Material and structural tests at ambient temperature have been conducted extensively on UHPC specimens in recent years, and its mechanical properties have been well-documented. In this study, a hybrid steel and polypropylene (PP) fibre reinforced UHPC is investigated under uniaxial and triaxial compression states after exposure to elevated temperatures. Cubic (50 mm) and cylindrical specimens (50 mm diameter × 100 mm height) were first heated in electric furnace to target temperatures, i.e. 200 °C, 400 °C, 600 °C, 800 °C and 1000 °C. After naturally cooled down to ambient temperature, the specimens were tested under uniaxial compression and triaxial compression with confining pressure ranging from 5 to 40 MPa. The triaxial stress–strain relationships and failure modes after exposure to elevated temperatures were then compared and discussed. Several common failure criteria for concrete material were adopted to describe the high temperature effect on UHPC's strength. An empirical model for reproducing the triaxial compression stress–strain curves of UHPC after elevated temperature was proposed.
Yang, G, Hu, X, Feng, Q & Nimbalkar, S 2021, 'Laboratory and Constitutive Modeling of Critical State Behavior of Rockfill Aggregates Mixed with Polymer', Journal of Testing and Evaluation, vol. 49, no. 6, pp. 4344-4356.
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Abstract In order to increase the strength and deformation properties of coarse aggregates, the polymer was used as an additive. In this study, a series of triaxial tests were performed to analysis the effect of polymer content on the strength, deformation, and critical state of rockfill aggregates. It is found that the deformation properties are the same for different polymer contents. As the polymer content increases, the peak stress increases, and the volume strain decreases. The addition of polymer mainly led to inducing cohesion in rockfill aggregates while showing a marginal influence on friction angle. The average effective stress, which considered the cohesion of polymer as additional effective stress, was modified. It was observed that the critical state envelopes in q–p′pc and e–p′pc were not much influenced by the addition of polymer. A state parameter is used as a function of void ratio and pressure. A boundary surface model of polymer rockfill aggregates based on the critical state approach was proposed. The performance of the model is demonstrated by the results of triaxial tests. The study shows the model could effectively capture the influence of polymer contents and confining pressures on strength and deformation characteristics of rockfill aggregates.
Yang, Y, Wu, C, Liu, Z, Qin, Y & Wang, W 2021, 'Comparative study on square and rectangular UHPFRC-Filled steel tubular (CFST) columns under axial compression', Structures, vol. 34, pp. 2054-2068.
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This paper presents an experimental study on the axial performance of square/rectangular concrete-filled steel tubular (CFST) columns. A total of 34 specimens, classified as four groups, were fabricated and tested under uniaxial compression. The failure modes, axial stress–strain curves, ultimate axial stress, and ductility were analysed in detail considering the effect of the steel ratio, steel fibre addition, concrete type, cross-section type, and size of the specimens. Further, the confinement index (ξ) and strength index (SI) was discussed. The obtained findings revealed that the ultimate axial stress of CFST columns was increased by increasing the thickness of the steel tube and adding steel fibres to the concrete mixture. When the steel ratio, steel tube thickness, and specimen height were the same, the type of cross-section (the square and the rectangular section) exhibited an insignificant effect on the axial stress–strain of the CFST column. Finally, a formula was proposed to estimate the ultimate axial stress of both square and rectangular CFST columns, with the concrete core strength ranging from 70 MPa to 150 MPa.
Ye, F, He, X, Zheng, J, Li, Y, Li, M, Hu, Z, Wang, S, Tong, G & Li, X 2021, 'Highly stretchable and self-foaming polyurethane composite skeleton with thermally tunable microwave absorption properties', Nanotechnology, vol. 32, no. 22, pp. 225703-225703.
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Abstract Stretchable and lightweight polymer composite material possessing tunable microwave absorption (MA) properties under thermal radiations remain a significant challenge. Here, we proposed a facile strategy to fabricate stretchable, magnetic composite skeletons by incorporating the tadpole-like CNTs@Fe3O4 nanoparticles into self-foaming polyurethane (PU) matrix and the electromagnetic responsive of CNTs@Fe3O4/PU composite foams with different CNTs contents under heating−cooling cycle in a temperature range of 253 −333 K were carefully investigated. Enhanced complex permittivity and shifting peak frequency were observed at elevated temperatures. For instance, the 70-CNTs@Fe3O4/PU sample with 15 wt% loading content at 333 K exhibits excellent MA properties including a minimum reflection loss (RLm) of −66.9 dB and ultrabroad effective frequency bandwidth (RL ≤ −20 dB) of 9.98 GHz at the thickness of 1.58−3.37 mm. Meanwhile, great recoverability in terms of RL-f profile was achieved in the process of thermal cooling back to 253 K. Such adjustable MA property was attributed to the well-matched impedance and dramatic attenuation ability, benefiting from the temperature-dependant electrical conductivity, abundant interfacial polarization and interior microcellular structures. Besides, the rising temperature increased the sample elongation and electrical conductivity with a slight sacrifice of maximum tensile strength. This stretchable PU skeleton with a unique assembly of CNTs and Fe3O4 nanoparticles are expected to be promising candidates as smart absorbers for application in the harsh environments.
Yu, Y, Nguyen, TN, Li, J, Sanchez, LFM & Nguyen, A 2021, 'Predicting elastic modulus degradation of alkali silica reaction affected concrete using soft computing techniques: A comparative study', Construction and Building Materials, vol. 274, pp. 122024-122024.
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Alkali silica reaction (ASR) is a harmful distress mechanism which results in expansion and reduction of mechanical properties of concrete. The latter may cause loss of serviceability and load carrying capacity of affected concrete structures. Influences of ASR on concrete are known to be complex in nature, for which the traditional empirical and curve-fitting approaches are insufficient to provide adequate models to capture such complexity. Recent advancement in soft computing (SC) offers a new tool for tackling the complexity of ASR affected concrete. Most of previous experimental studies agreed that as a result of ASR, the elastic modulus suffers a significant reduction compared with other properties such as compressive and tensile strength of the affected concrete. In this study, an investigation has been conducted, utilising different SC models to quantify ASR-induced elastic modulus degradation of unrestrained concrete. Five SC techniques, namely support vector machine (SVM), artificial neural network (ANN), adaptive neuro-fuzzy inference system (ANFIS), M5P model and genetic expression programming (GEP), are investigated comparatively in this research. The models, on basis of SC techniques, are developed and tested using a comprehensive dataset collected from existing publications. In order to demonstrate the superiorities of SC techniques, the proposed approaches are compared to several empirical models developed using same dataset. The comparative results show that the developed SC models outperform empirical models in a wide range of evaluation indices, which indicates promising applications of the proposed approach.
Yu, Y, Yousefi, AM, Yi, K, Li, J, Wang, W & Zhou, X 2021, 'A new hybrid model for MR elastomer device and parameter identification based on improved FOA', Smart Structures and Systems, vol. 28, no. 5, pp. 617-629.
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A new hysteresis model based on curve fitting method is presented in this work to portray the greatly nonlinear and hysteretic relationships between shear force and displacement responses of the magnetorheological (MR) elastomer base isolator. Compared with classical hysteresis models such as Bouc-Wen or LuGre friction model, the proposed model combines the hyperbolic sine function and Gaussian function to model the hysteretic loops of the device responses, contributing to a great decline of model parameters. Then, an improved fruit fly optimization algorithm (FOA) is proposed to optimize the model parameters, in which a self-adaptive step is employed rather than the fixed step to balance the global and local optimum search abilities of algorithm. Finally, the experimental results of the device under both harmonic and random excitations are used to verify the performance of the proposed hybrid model and parameter identification algorithm with the satisfactory results.
Zhang, X & Fatahi, B 2021, 'Assessing axial load transfer mechanism of open-ended tubular piles penetrating in weak rocks using three-dimensional discrete element method', Computers and Geotechnics, vol. 137, pp. 104267-104267.
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Zhang, X, Tang, Z, Ke, G & Li, W 2021, 'Mechanical Properties and Durability of Sustainable Concrete Containing Various Industrial Solid Wastes', Transportation Research Record: Journal of the Transportation Research Board, vol. 2675, no. 12, pp. 797-810.
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Benefits of replacing ordinary Portland cement with industrial solid wastes are promising for reducing cement production and solving environmental problems associated with industrial solid wastes. In this study, an experimental investigation was conducted to evaluate the performance of sustainable concrete containing different industrial solid wastes (e.g., waste glass, coal gangue, fly ash, and slag), with the attention on the mechanical strength, chloride transport property, and pore structure characteristics. Three water to binder ratios (i.e., 0.38, 0.48, and 0.65) and three replacement levels (i.e., 10%, 20%, and 30%) were considered in this work. The test results show that regardless of the content and type of industrial solid wastes, the inclusion of industrial solid wastes generally exerts a negative influence on the mechanical properties, especially under high water to binder ratios. However, acceptable mechanical strength can still be achieved in these sustainable concretes. In addition, the inclusion of industrial solid wastes could enhance the chloride diffusion resistance of concrete, and also the concrete with waste glass powder showed the best performance. Furthermore, the incorporation of industrial solid wastes has a refinement effect on the microstructure of the matrix, manifesting as decreased cumulative pore volume and compacted microstructural morphology.
Zhao, E & Wu, C 2021, 'Centroid deformation-based nonlinear safety monitoring model for arch dam performance evaluation', Engineering Structures, vol. 243, pp. 112652-112652.
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The purpose of this study is evaluating the arch dam performance through modelling on the defined centroid deformation with the measured data. The space-time distribution characteristics of the arch dam deformation are firstly identified through the comparative analysis of typical arch dams with height of 200–300 m in China. Subsequently, the geometry centroid of the deflection curve of an arch or a cantilever, composed of multiple monitoring points, is defined to indicate the global structural behavior of the arch dams. In order to evaluate the future performance of the arch dams, the space–time monitoring model for the centroid is established by introducing its initial coordinates based on the traditional statistical models. Afterwards, a novel centroid prediction model is developed based on the least squares support vector machine to balance the empirical risk and generalization ability of the statistical regression models. The input factors of the prediction model are determined in advance by principal component analysis to eliminate the multi-collinearity and reduce the computational complexity. The model construction and validation of the centroid deformation method are implemented on the world's highest arch dam through evaluating its structural behavior and predicting the development trend. The results can provide strong technical support to better grasp its performance during long-term operation.
Zhao, E & Wu, C 2021, 'Long-term safety assessment of large-scale arch dam based on non-probabilistic reliability analysis', Structures, vol. 32, pp. 298-312.
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Zhao, E & Wu, C 2021, 'Risk probabilistic assessment of ultrahigh arch dams through regression panel modeling on deformation behavior', Structural Control and Health Monitoring, vol. 28, no. 5.
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Boyd-Weetman, B, Thomas, P & Sirivivatnanon, V 1970, 'Evaluation of the effect of alkali bath concentration on ASR development in AMBT', Concrete Institute of Australia's Biennial National Conference 2021, Perth - Virtual.
Boyd-Weetman, B, Thomas, P, Sirivivatnanon, V & Nairn, J 1970, 'Alkali thresholds in concrete; the balanced alkali approach in ASRmitigation', Proceedings of the 16th International Conference on Alkali-Aggregate Reaction in Concrete, International Conference on Alkali-Aggregate Reaction in Concrete, LABORATÓRIO NACIONAL DE ENGENHARIA CIVIL, I. P., Lisbon, pp. 611-616.
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The Alkali Silica Reaction (ASR) is a deleterious reaction in concrete that poses significant durability concern worldwide. As a preventative measure, total alkali content of general purpose Portland cements can be limited. In Australia, like in other countries, general purpose cement is limited with a conservative alkali content of 0.6%, this may be unnecessary, as low risk non-reactive aggregates and SCM blends are effective in reducing ASR prevalence. Indeed there is a growing argument to transition to risk assessed methods in choosing cement alkali levels. ASTM in the USA has employed a prescriptive approach to selecting preventative measures that incorporates a variety of cement alkali contents without compromising on safety. Similar balanced alkali approaches such as those recommended in Europe, Canada and New Zealand may be applicable in Australia. Raising alkali limits to a level greater than 0.6% in cement used in conjunction with alternative mitigation techniques would reduce the economic and environmental impact associated with alkali removal during cement production. This literature review discusses the Australian approach to alkali limits in contrast to the methods used around the world and explores the continuing research into alkali’s mechanistic contribution to ASR.
Doan, S, Fatahi, B & Khabbaz, H 1970, 'Exact Series Solution for Plane Strain Consolidation of Stone Column Improved Soft Soil Accounting for Space-Dependent Total Stresses', Lecture Notes in Civil Engineering, International Conference on Computer Methods and Advances in Geomechanics, Springer International Publishing, Virtual, pp. 794-802.
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This paper provides an analytical solution to predict the free strain consolidation of a stone column supported soft soil under plane strain configuration. The external load on the ground surface was assumed to be applied instantly, which results in time-independent but space-dependent total stresses in the composite ground. A rigorous analytical solution to evaluate the changes of excess pore water pressure with time at any point in the model was derived as a double series, using the method of separation of variables. The obtained solution can capture any distribution patterns of total stresses caused by the external load, where the total stresses are described as separable functions against spatial coordinates. The validation of the proposed solution was exhibited through an example evaluating the effect of change patterns of the total stresses with depth on consolidation of the composite ground. The calculation results were presented graphically in terms of average degree of consolidation for column and for soft soil, and average differential settlement between the column and soil regions. The more diminution of the total stresses with depth led to accelerated consolidation of the composite ground and more significant reduction in the average differential settlement between the column and the soil.
El-Hawat, O, Fatahi, B & Mostafa, M 1970, 'Effect of Near-Fault Vertical Ground Motions on the Seismic Response of Bridges with Rocking Foundations', Springer Singapore, pp. 95-107.
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Rocking foundations can be used in bridges to reduce the seismic demand of the structure and prevent inelastic behaviour from developing at the piers during large earthquake events. Several studies have proven that rocking is an effective seismic isolation technique under lateral earthquake loading. However, limited research has been conducted on the effect of the vertical component of earthquakes on the rocking behaviour of bridge piers. This paper aims to numerically investigate the effect of the vertical component of near-fault earthquakes on the seismic performance of bridges with rocking pile foundations. Two identical bridge configurations with different foundation systems (conventional fixed base foundation and rocking foundation) are subjected to two loading cases: (1) horizontal ground motions only, (2) combined horizontal and vertical ground motions. Three-dimensional models of the bridges are developed with the appropriate material models to capture possible inelastic behaviour, as well as to model the soil–structure interaction. Four near-fault ground motions with three components are selected and scaled to the appropriate seismic hazard and applied to the bridges using nonlinear dynamic time history analyses. The dynamic responses of the bridges are compared in terms of deck displacements, deck bending moments, and pier axial and bending moments. The results show that the vertical component of ground motions can considerably increase the dynamic response of the bridge with the rocking foundation when compared to the fixed base foundation, leading to increased deck displacements and inertial actions on the bridge structure.
Gowripalan, N, Cao, J, Sirivivatnanon, V & South, W 1970, 'Comparison of the effect of ASR deterioration on the load carrying capacity of concrete structural elements in accelerated laboratory tests and in the field', First Book of Proceedings of the 16th ICAAR, International Conference on Alkali Aggregate Reaction, LABORATÓRIO NACIONAL DE ENGENHARIA CIVIL, Lisbon, Portugal, pp. 1245-1257.
JARADAT, Y, FAR, H & SALEH, ALI 1970, 'EXAMINING THE ADEQUACY OF SEPARATION GAPS BETWEEN ADJACENT BUILDINGS UNDER NEAR-FIELD AND FAR-FIELD EARTHQUAKES', WIT Transactions on The Built Environment, ERES 2021, WIT Press, pp. 59-71.
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Li, H, Li, J, Li, Y & Yu, Y 1970, 'Dynamic Property Optimization of a Vibration Isolator with Quasi-Zero Stiffness', Vibration Engineering for a Sustainable Future, Asia-Pacific Vibration Conference, Springer International Publishing, Australia, pp. 289-295.
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For a linear vibration isolator, it is a dilemma to accomplish low transmissibility for effective vibration isolation and meanwhile to provide sufficient loading support, especially under low and ultralow frequency range. Adopting a class of vibration isolators with quasi-zero stiffness (QZS) is verified as a potential solution since it is designed with low-dynamic stiffness that contributes to low natural frequency, while its high-static stiffness can maintain sufficient loading support. This paper conducts an in-depth exploration of the dynamic properties of a compact QZS vibration isolator (QZSVI) that consists of two oblique springs and one vertical spring. Its dynamic properties including resonance frequency, amplitude-frequency response (AFR), and force transmissibility are obtained by employing the harmonic balance method. Following that, a comprehensive objective function considering three property parameters is proposed to optimize its dynamic property. The optimization results under different damping ratios are obtained and discussed at the end of this paper.
Liu, Z, Wu, D, Sheng, D, Fatahi, B & Khabbaz, H 1970, 'MACHINE LEARNING AIDED STOCHASTIC SLOPE STABILITY ANALYSIS', 4th International Conference on Uncertainty Quantification in Computational Sciences and Engineering, 4th International Conference on Uncertainty Quantification in Computational Sciences and Engineering, Institute of Research and Development for Computational Methods in Engineering Sciences (ICMES), Streamed from Athens, Greece,, pp. 75-81.
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This paper presents the study in the machine learning aided stochastic slope stability analysis through the finite element method. The probability of failure of a dam with cohesive slope has been investigated. The numerical model has been built by the finite element method. An advanced machine learning algorithm called Extreme Learning Machine (ELM) is adopted to establish the regression model. The applicability and effectiveness of the presented approach are compared by the Monte-Carlo simulation method.
Mansell, B, Thomas, P, Li, Y, Tapas, MJ & Holt, C 1970, 'The impact of accelerating admixtures on blended cement hydration for early age strength enhancement', Concrete Institute of Australia's Biennial National Conference 2021, Concrete Institute of Australia's Biennial National Conference 2021, Perth - Virtual.
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With an ever-increasing focus on sustainable concrete, the use of supplementary cementitious materials (SCMs) has grown and, although SCMs provide improved later age properties, their use can result in reduced early age strength. Chemical admixtures, particularly those that accelerate hydration processes, have the potential to address these deficiencies. Examples of these opportunities for greater early age strength systems have been identified in the literature, whether through the development of new research and commercial products, or through the creative application of existing admixtures. Conventional inorganic and organic accelerators can be applied in novel high order combinations that exhibit a synergistic effect on early strength. A major focus in the literature at present is the use of C-S-H seeds in superplasticiser suspensions or composites, which can elicit very early strength improvement. Such nucleating agents provide sites for hydrate product growth, potentially leading to denser microstructures and improved early age mechanical properties. In this paper, key studies from the past decade are reviewed, covering the application of a range of accelerating admixtures to the enhancement of early age strength in blended cements.
Martin, L, Thomas, P, Nairn, J & Sirivivatnanon, V 1970, 'Calorimetric Study into the Role of Alkali and Sulfate in the Early Hydration of Heat-cured GP Cements and Associated Susceptibility to DEF', Concrete Institute of Australia's Biennial National Conference 2021, Perth - Virtual.
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Durability of concrete structures is an important issue in the modern world, with the performance of concrete as a construction material significantly impacting its environmental, economic, and social costs. Understanding of the chemical behaviour of concrete informs the prevention and mitigation of potential causes of durability loss. Delayed e ttringite f ormation (DEF) is a chemical process in concrete that can cause expansion, microcracking and strength loss. It is a known risk of durability loss, in particular with precast concrete. The primary mechanism of DEF is the dissolution of the sulfate mineral ettringite during early hydration and subsequent re-precipitation as an expansive phase in hardened cement paste. The major factors of DEF relate to the saturation of the pore solution with sulfate ions. Primary factors that influence sulfate solubility are alkalinity and temperature, particularly in the early stage of hydration. Factors that influence the ettringite formation are aluminate and sulfate, and their content ratios. DEF is mainly initiated in the manufacturing process of precast elements and is a consequence of phase development during hydration. Isothermal calorimetry provides a way to monitor cement paste hydration and to investigate the role of alkali and sulfate content in phase development. This paper present s the outcomes of a study on the influence of these chemical factors on the hydration process and correlate s this with phasedevelopment by characterisation of phases using XRD and TGA in paste compositions that are both DEFfree and at-risk of deleterious DEF.
Nguyen, T, Li, J, Gowripalan, N & Sirivivatnanon, V 1970, 'Assessing Structural Performance Of Existing Concrete Structures Damaged By Asr', Concrete Institute of Australia's Biennial National Conference 2021SUNDAY, Concrete Institute of Australia's Biennial National Conference 2021SUNDAY, Virtual Conference.
Nsiah-Baafi, E, Tapas, MJ, Vessalas, K, Thomas, P & Sirivivatnanon, V 1970, 'Mitigation of ASR using aggregate fines as an alternative for SCMs', Proceedings of the 16th International Conference on Alkali-Aggregate Reaction in Concrete, 16th International Conference on Alkali-Aggregate Reaction in Concrete, LABORATÓRIO NACIONAL DE ENGENHARIA CIVIL, I. P., Lisbon, pp. 423-431.
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The use of supplementary cementitious materials (SCMs) for mitigating alkali-silica reaction (ASR) isthe most common and practical approach adopted by concrete producers since the early 1950s [1].However, with the future supply of commonly available SCMs such as fly ash and ground granulatedblast furnace slag set to decline, alternative materials for mitigating ASR needs to be considered. Theobjective of this experimental work is to investigate the potential of using ground reactive aggregatefines as SCM substitutes to mitigate ASR. The mechanism of mitigation has been investigated usingcharacterization and expansion tests assessed under AMBT conditions. Mortar bars containing 0%,10%, 25% and 40% ground reactive aggregate fines by mass of cement replacement were prepared formodified accelerated mortar bar testing. The results obtained indicated that a reduction in ASRexpansion was achieved with increasing ground reactive aggregate fines content. Furthercharacterization including XRF and ICP-OES analyses were carried out on ground reactive aggregatefines to understand the efficacy of these materials as potential additives for ASR mitigation.
Nsiah-Baafi, E, Vessalas, K, Thomas, P & Sirivivatnanon, V 1970, 'Correlation between Existing Test Methods for Assessing Alkali-Silica Reaction of Aggregates', Concrete Institute of Australia Biennial National Conference, Concrete 2021, Perth - Online.
Nsiah-Baafi, E, Vessalas, K, Thomas, P & Sirivivatnanon, V 1970, 'Protocols for investigating the reactivity of aggregates and alkali thresholds for ASR prevention', Proceedings of the 16th International Conference on Alkali-Aggregate Reaction in Concrete, 16th International Conference on Alkali-Aggregate Reaction in Concrete, LABORATÓRIO NACIONAL DE ENGENHARIA CIVIL (LNEC), Lisboa, pp. 689-698.
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Alkali in concrete pore solution and reactive silica in aggregate are integral features required for alkalisilicareaction (ASR). When high amounts of alkali are present, expansive ASR gel forms that causecracking of concrete. Thus, limits have been imposed, restricting allowable alkali contents for use inconcrete. However, these limits are known to be generalised with a single limit specified for all aggregatetypes. This study investigates the reactivity potential and critical alkali threshold for individual aggregatesand aggregate combinations, by increasing alkali content (0.60-1.25% Na2Oe) in concrete, varyingexposure temperature (38-80°C) and extending test duration. A combination of RILEM recommendedmethods and modified versions of the standard accelerated mortar bar test (AMBT) and concrete prismtest (CPT) expansion test methods have been used. The key findings of this study suggest that thepotential exists for specifying a determined alkali threshold in concrete based on the reactivityclassification of aggregates used, thus, allowing a relaxation of the current alkali limit for concrete. Thisapproach permits greater flexibility in the potential safe use of reactive aggregates in concrete.Furthermore, this study shows that the determination of an aggregate’s reactivity and potential to ASRis not only highly dependent on its chemical composition and the alkali content in the concrete but alsothe test method, exposure temperature and test storage age used to assess changes in expansion.
Omar, KR, Fatahi, B & Nguyen, LD 1970, 'Investigation on the Mechanical Properties of Low Plasticity Clay Contaminated with Engine Oil', Springer International Publishing, pp. 21-32.
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Ramu, Y, Thomas, P & Sirivivatnanon, V 1970, 'Pore solution chemistry of expansive heat cured cementitious systems', Proceedings of the 4th International RILEM conference on Microstructure Related Durability of Cementitious Composites (Microdurability2020), International RILEM conference on Microstructure Related Durability of Cementitious Composites (Microdurability2020), TUDeft, The Hague, The Netherlands, pp. 212-219.
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Heat cured cement mortars may result in linear expansion due to later age ettringite precipitation, popularly termed as delayed ettringite formation (DEF). However, later age ettringite precipitation may not result in expansion always. To differentiate the expansive and non-expansive nature of heat-cured cementitious systems, in this research pore solution chemistry of various cementitious systems cured at 90°C for 12 hours were studied. Linear expansion of mortar bars was measured periodically. Besides, ettringite precipitation was studied using X-ray diffraction (XRD) and thermal gravimetric analysis (TGA). The XRD, TGA results show the absence of early age ettringite and its delayed precipitation in all the heat-cured cementitious systems irrespective of expansive or non-expansive mortars. However, the pore solution ionic concentration reveals that sulphate ion concentration at the end of heat curing is vital to predicting whether the mortar will expand or not in the future. The curing temperature increased the solubility of sulphates and total alkalis present in the pore solution. The expanded mortars had relatively higher amount of sulphates in the pore solution at the age of 30 hours, compared to the non-expansive mortars. Further, at the age of 7 and 30 days, a drop in Sulphate, sodium, potassium ions concentration in pore solution was noticed, suggesting the leaching of alkalis and consumption of Sulphate for the precipitation of ettringite.
Ramu, Y, Thomas, P, Sirivivatnanon, V & Vessalas, K 1970, 'Role of fly ash in mitigating durability issues due to curing cement systems at elevated temperature', Concrete Institute of Australia Biennial National Conference, Concrete 2019, Perth - Online.
Rasouli, H & Fatahi, B 1970, 'Effect of Burial Depth on Pipeline-Fault Rupture Interaction Mechanism and Mitigation Technique Using Geofoam Blocks', Springer International Publishing, Switzerland, pp. 966-974.
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This paper presents the effect of burial depth on the response of conventional buried pipelines under strike-slip fault rupture and also proposes a mitigation method using geofoam blocks to safeguard buried pipelines. The performance of the buried pipelines is assessed using three-dimensional numerical simulation using ABAQUS. The configuration of geofoam blocks for protection consists of two blocks at each side of the pipeline and one block on the top of pipeline. The results shows that although the conventional buried pipeline failed due to fault rupture as a result of excessive compressive strain as well as local buckling within the pipe wall, geofoam blocks could successfully reduce the compressive and tensile strains along the pipeline satisfying the design requirements.
Rasouli, H & Fatahi, B 1970, 'Effect of Strike-Slip Fault Rupture on Piled Raft Foundation', Springer International Publishing, Switzerland, pp. 653-660.
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This paper presents the interaction mechanism of a 12-story building sitting on a piled raft foundation with a strike-slip fault rupture. The mechanical response of foundation including both structural and geotechnical response of the foundation are evaluated through three-dimensional numerical modelling using ABAQUS. The obtained results showed that the raft significantly suffers from rotation about the vertical axpipelinis and horizontal displacement. Both bending moment and shear forces in piles due to fault rupture exceeded the capacity values of piles. The maximum bending moment and shear forces within piles took place at the connection of piles to the raft and exceeded allowable values when the fault slipped more than 0.3 m.
Reja, VK, Bhadaniya, P, Varghese, K & Ha, QP 1970, 'Vision-Based Progress Monitoring of Building Structures Using Point-Intensity Approach', Proceedings of the 38th International Symposium on Automation and Robotics in Construction (ISARC), 38th International Symposium on Automation and Robotics in Construction, International Association for Automation and Robotics in Construction (IAARC).
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Shafaghat, A, Khabbaz, H & Fatahi, B 1970, 'Developing an Efficiency Equation for Tapered Pile Groups in Sand Using Mathematical and Numerical Analyses', Advances in Urban Geotechnical Engineering Proceedings of the 6th GeoChina International Conference on Civil & Transportation Infrastructures: From Engineering to Smart & Green Life Cycle Solutions -- Nanchang, China, 2021, GeoChina International Conference, Springer International Publishing, China, pp. 16-30.
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This study presents a new simple equation for prediction of pile group efficiency considering the effect of tapering angle in cohesionless soil under vertical loading. Firstly, a simple analytical relationship based on the mathematical definition of the pile group efficiency is developed. However, the effect of tapering angle is captured by defining a new geometry efficiency coefficient associated with the shaft vertical bearing component of tapered piles. Thereafter, a mathematical equation is developed by taking into account the shaft vertical bearing ratio and the new geometry efficiency coefficient. On the other hand, a numerical analysis is performed for modelling a single bored cylindrical pile and a tapered pile with the same volume as well as bored tapered pile groups to validate the proposed mathematical equation. The UBC sand constitutive model is adopted for the modelling of piles in loose Cambria sand. Subsequently, the load-displacement diagrams of single and group of piles are obtained. Then, the bearing capacities of cylindrical and tapered bored piles both as single and group are computed and compared, using a specific settlement criterion. Besides, the friction resistance ratio and the shaft vertical bearing ratio are separated, applying numerical methods. Having calculated the ratios of various components of bearing capacity, pile group efficiencies can be obtained from both numerical and mathematical models. The results show that the proposed equation can predict the pile group efficiency incorporating the tapering angle as well as other influencing parameters as a simple and novel relationship.
Slattery, TP, Cowled, CJL, Crews, K & Brooke, H 1970, 'Preliminary experimental study of midply trussed shear walls', World Conference on Timber Engineering 2021, WCTE 2021.
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The lateral restraint system in mid-rise timber buildings must be designed for higher loads, due to wind and earthquake, than that of low-rise buildings. In this preliminary experimental study, we report on the racking performance of a midply trussed shear wall prototype with an X configuration. The mean ultimate capacity of this prototype is 56.9 kN/m and the design capacity is estimated as 45.5 kN/m, a substantial improvement on typical timber-framed shear wall systems.
Song, Z, Mortazavi, M, Tapas, MJ, Moghaddam, F & Sirivivatnanon, V 1970, 'Particle Packing Theory in Ultra-sustainable Concrete with High SCM Content', Concrete Institute of Australia's Biennial National Conference 2021, Online.
Tapas, MJ, Nsiah-Baafi, E, Vessalas, K, Thomas, P & Sirivivatnanon, V 1970, 'Reactive Aggregate Fines as Alternative Supplementary Cementitious Material for Alkali Silica Reaction (ASR) Mitigation', Concrete Institute of Australia Biennial National Conference, Concrete 2021, Concrete Institute of Australia Biennial National Conference, Concrete 2021, Perth - Online.
Tapas, MJ, Sofia, L, Vessalas, K, Thomas, P, Sirivivatnanon, V & Scrivener, K 1970, 'Alternative Test Method for Assessing Alkali-Silica Reaction and the Efficacy of Supplementary Cementitious Materials in ASR Mitigation', Concrete Institute of Australia Biennial National Conference, Concrete 2021, Perth - Online, pp. 1-8.
Tapas, MJ, Sofia, L, Vessalas, K, Thomas, P, South, W, Sirivivatnanon, V & Scrivener, K 1970, 'The ability of SCMs to mitigate ASR in cements of higher alkali contents assessed by pore solution method', Proceedings of the 16th International Conference on Alkali-Aggregate Reaction, 16th International Conference on Alkali-Aggregate Reaction, LABORATÓRIO NACIONAL DE ENGENHARIA CIVIL, I. P., Lisbon, pp. 595-600.
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This study reports on the efficacy of supplementary cementitious materials (SCMs) to mitigate ASRwhen used in conjunction with cement of higher alkali contents (up to 1%Na2Oeq). The expansion ofconcrete prisms immersed in simulated pore solution was studied in order to address the limitations ofconventional ASR testing methods AMBT and CPT. The alkali concentration in the simulated poresolution was derived from the 28-day age pore solution of pastes with equivalent composition as theconcrete binder of interest. The concrete prisms were prepared using Australian sourced materials:2 types of reactive aggregates (dacite and rhyolite), 2 types of SCMs (fly ash and slag) and cement with0.6% Na2Oeq original alkali content that was boosted with alkali to obtain 1.0% Na2Oeq. The concreteprisms were stored at 38 °C and at 60 °C. Expansion results show that 25% fly ash and 50% slag areboth sufficient to mitigate ASR even with cements with alkali content up to 1.0%Na2Oeq. Extensiveamount of ASR products were observed in concretes without SCMs. Small amount of ASR productswere also observed in concrete with SCMs, even if there was no notable expansion observed.
Tapas, MJ, Thomas, P, Fu, J, Chandler, J, Sirivivatnanon, V & Keyte, L 1970, 'High Early Strength Gain Low-carbon Concrete: A Microstructure Study', Concrete Institute of Australia Biennial National Conference, Concrete 2021, Concrete Institute of Australia Biennial National Conference, Concrete 2021, Perth - Online.
Tapas, MJ, Vessalas, K, Thomas, P & Sirivivatnanon, V 1970, 'Dissolution behaviour of SCMs in alkaline environment and mechanisms behind ASR mitigation', Proceedings of the 16th International Conference on Alkali-Aggregate Reaction in Concrete, International Conference on Alkali-Aggregate Reaction in Concrete, LABORATÓRIO NACIONAL DE ENGENHARIA CIVIL, I. P., Lisbon, pp. 423-430.
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Fly ash and slag are supplementary cementitious materials (SCMs) commonly used to mitigate alkali-silica reaction (ASR). However, future supply of these SCMs is at risk due to a global push to reduce coal-fired energy production and increased steel recycling. Thus, an immediate need to identify alternative SCMs is critical. In order to establish the efficacy of an SCM in its ability to mitigate ASR, an understanding of the chemical processes involved in ASR mitigation is required. This study aims to better understand the mechanisms behind ASR mitigation by comparing the amount of silicon (Si) and aluminium (Al) released by SCMs under AMBT conditions, investigating the interaction of the dissolvedSCM species in the system (i.e. formation of reaction products) and how these correlate to explain thedifferences in SCM dosage requirements for effective mitigation. Results show that the ability of SCMs to release Si is as follows: SF>MK>FA>SL which correlates well with the dosage required to mitigate ASR. This indicates that the efficacy of SCMs in mitigating ASR is primarily due to their ability to release Si in solution. Formation of sodium aluminium silicate hydrate (N-A-S-H) in fly ash and metakaolin and formation of calcium aluminium silicate hydrate (C-A-S-H) in slag post alkali immersion were also observed. This indicates the ability of aluminium to bind silicon and precipitate alkali in theprocess (effectively reducing solution alkali concentration) and highlights its beneficial effect on ASRmitigation. Further, in systems saturated with calcium, Ca is bound instead of Na suggesting the occurrence of competitive reactions and subsequent alkali recycling. Calcium, therefore, does not appear to have a beneficial effect on ASR mitigation.
Thomas, P 1970, 'Structural Properties of Precious Opal', 2020 Vision 10th National Opal Symposium, Coober Pedy.
Tran Thanh, H, Li, J & Zhang, YX 1970, 'Numerical Evaluation the Effect of Specimen Thickness on Fibre Orientation in Self-consolidating Engineered Cementitious Composites', RILEM Bookseries, Springer International Publishing, pp. 661-669.
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The orientation of distributed synthetic fibres in the matrix of engineered cementitious composites (ECCs) governs their capability of bearing stress and bridging micro-cracks. Understanding the orientation of synthetic fibres in ECCs matrix of different thickness specimens, therefore, is necessary. In the present work, the effect of specimen thickness on the orientation of synthetic fibres in self-consolidating (SC) ECC, a typical member of family ECC materials, is numerically investigated through the simulation of the casting of fresh SC-ECC into different thicknesses of moulds. The moulding of fresh SC-ECC, which is discretised by a limit number of separated mortar and fibre particles, is simulated using the mesh-free smoothed particle hydrodynamics (SPH) method. The synthetic fibre utilised in SC-ECC is considered as flexible fibre and virtually connected by a drag force between two adjacent fibre particles. The SPH allows tracking the movement of mortar and fibre particle during their flow, thus providing the real image of flexible synthetic fibres orientation in specimens during the casting process. A simple method is proposed to evaluate the orientation of flexible synthetic fibres at various sections of specimens after the SC-ECC stop flowing in the moulds. The results of this study reveal that thin specimens tend to have higher fibre orientation factors than thick specimens. Synthetic fibres tend to parallel with the longitudinal direction of specimens at the bottom of the formwork and rotate freely at the top surface of specimens.
