Alamdari, MM, Li, J, Samali, B, Ahmadian, H & Naghavi, A 2014, 'Nonlinear Joint Model Updating in Assembled Structures', Journal of Engineering Mechanics, vol. 140, no. 7, pp. 04014042-04014042.
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Dynamic response of mechanical structures is significantly affected by joints. Joints introduce remarkable frictional damping and
localized flexibility to the structure; hence, to obtain a more accurate representation of a system’s dynamics, it is crucial to take these effects into
account. This paper investigates the application of finite-element model updating on characterization of a nonlinear joint interface. A thin layer
of virtual elements is used at a joint location to represent the nonlinear behavior of the coupling in the tangential direction. The material
properties of the elements are described by a nonlinear constitutive stress-strain equation that defines the nonlinear state of the joint interface. In
this study, Richard–Abbot elastic-plastic material was considered, which is capable of characterizing energy dissipation and softening
phenomena in a joint at a nonlinear state. Uncertain material parameters are adjusted to minimize the residual between the numerical and
experimental nonlinear frequency responses. Minimization was carried out based on iterative sensitivity-based optimization. The procedure was
implemented on an assembled structure consisting of two steel threaded pipes coupled to each other by a nut interface. It was demonstrated that
the proposed technique significantly reduced the uncertainties in the joint modeling and led to a more reliable description of the assembled
structure.
Alamdari, MM, Li, JC & Samali, B 2014, 'A Novel FRF-Based Damage Localisation Method Using Random Vibration', Applied Mechanics and Materials, vol. 553, pp. 713-718.
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This paper presents a novel damage localization method based on the measured Frequency Response Functions (FRFs) without demanding any previous data records of the structure in its healthy state. The main innovation of this study starts with reconstruction of FRFs curvature to develop spatial shape functions. It is demonstrated that reconstructed data significantly magnifies the influence of low-frequency spectra in damage detection procedure which is considered the milestone of this approach as excitation of the higher frequencies is not easy to obtain in most practical applications. The modified curvature data in all measured frequencies and locations is interpreted as a two dimensional image and then processed by employing 2-D discrete wavelet transform to detect any abrupt variation at damage site. Level one wavelet decomposition is utilised to provide the finest detail coefficients. It is illustrated that this approach presents a more recognizable pattern at damage site in all measured frequencies. The pattern can be described by a horizontal line parallel to the frequency spectra in 2-D image. Hence, the horizontal detail coefficients are utilised to detect this pattern as they are more sensitive to perturbation with orientation parallel to horizontal axis in the image. The main contribution of this approach lies in the fact that the proposed technique is able to detect the structural damage in all measured frequencies and the effectiveness of the method is independent of the excitation location. Moreover, the results provide a better visualisation at damage site which other FRF-based damage detection methods could not obtain. Applying broadband FRF data in this approach and the fact that there is no need for data from the healthy state of the structure are other advantages accompanying this method. The robustness of the proposed damage identification method was examined with various damage conditions in both single and multiple states. Mo...
Aslani, F, Nejadi, S & Samali, B 2014, 'Long-term flexural cracking control of reinforced self-compacting concrete one way slabs with and without fibres', COMPUTERS AND CONCRETE, vol. 14, no. 4, pp. 419-444.
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Aslani, F, Nejadi, S & Samali, B 2014, 'Short term bond shear stress and cracking control of reinforced self-compacting concrete one way slabs under flexural loading', COMPUTERS AND CONCRETE, vol. 13, no. 6, pp. 709-737.
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Fibre-reinforced self-compacting concrete (FRSCC) is a high-performance building material that combines positive aspects of fresh properties of self-compacting concrete (SCC) with improved characteristics of hardened concrete as a result of fibre addition. To produce SCC, either the constituent materials or the corresponding mix proportions may notably differ from the conventional concrete (CC). These modifications besides enhance the concrete fresh properties affect the hardened properties of the concrete. Therefore, it is vital to investigate whether all the assumed hypotheses about CC are also valid for SCC structures. In the present paper, the experimental results of short-term flexural load tests on eight reinforced SCC and FRSCC specimens slabs are presented. For this purpose, four SCC mixes - two plain SCC, two steel, two polypropylene, and two hybrid FRSCC slab specimens - are considered in the test program. The tests are conducted to study the development of SCC and FRSCC flexural cracking under increasing short-term loads from first cracking through to flexural failure. The achieved experimental results give the SCC and FRSCC slabs bond shear stresses for short-term crack width calculation. Therefore, the adopted bond shear stress for each mix slab is presented in this study. Crack width, crack patterns, deflections at mid-span, steel strains and concrete surface strains at the steel levels were recorded at each load increment in the post-cracking range. Copyright © 2014 Techno-Press, Ltd.
Cassidy, MJ, Gaudin, C, Bates, L, Indraratna, B, Nimbalkar, S, O'Loughlin, CD, White, DJ & Sloan, SW 2014, 'Advancing Australia's facilities for physical modelling in geotechnics', Australian Geomechanics Journal, vol. 49, no. 4, pp. 3-12.
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This paper presents details of the advancements of the Australian Research Council Centre of Excellence for Geotechnical Science and Engineering to the apparatus, facilities and methods for physical modelling in geotechnics. This advancement includes (i) the launch of a National Geotechnical Centrifuge Facility with a new 10 m diameter fixed beam centrifuge that will be capable of spinning 2.4 tonnes of soil at 100 gravities, (ii) a new mobile soft soil in situ testing laboratory, (iii) a new national facility for the cyclic testing of high-speed rail and (iv) three recirculating flumes, called O-tubes, which are presented in another paper of this special issue. This paper provides an overview of this new equipment and the aims of the research that it will underpin. The equipment will provide enhanced possibilities for Australia to conduct project specific testing for future energy and transportation infrastructure developments, nationally and internationally.
Dackermann, U, Crews, K, Kasal, B, Li, J, Riggio, M, Rinn, F & Tannert, T 2014, 'In situ assessment of structural timber using stress-wave measurements', MATERIALS AND STRUCTURES, vol. 47, no. 5, pp. 787-803.
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This paper summarizes the test recommendations for in situ assessment of structural timber using stress wave measurements as developed by members of the RILEM Technical Committee AST 215 ``In-situ assessment of structural timber. In the first part, the basic principles, the equipment, and the practical application of stress-wave-based testing using the time-of-flight method are described. A detailed testing procedure provides hands-on information on the execution of in-field stress wave testing. A typical example is given to demonstrate step-by step on how to evaluate stress wave readings and the health state of the inspected timber member. The latter part of the paper gives a short overview of the use of acoustic tomography and ultrasonic echo methods.
Dragos, J & Wu, C 2014, 'Application of Normalized Pressure Impulse Diagrams for Vented and Unvented Confined Blasts', Journal of Engineering Mechanics, vol. 140, no. 3, pp. 593-603.
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Dragos, J & Wu, C 2014, 'Interaction between direct shear and flexural responses for blast loaded one-way reinforced concrete slabs using a finite element model', Engineering Structures, vol. 72, pp. 193-202.
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In this paper, both the moment-curvature flexural behavior and the direct shear behavior are incorporated into a numerically efficient one dimensional finite element model, utilizing Timoshenko Beam Theory, to determine the member and direct shear response of one-way reinforced concrete slabs subjected to blasts. The model is used to undertake a case study to demonstrate the flexural member response behavior during the direct shear response and is then used to carry out a parametric study to better understand the interaction of the flexural member response and the direct shear response. This is done by comparing pressure impulse curves corresponding to direct shear failure for one-way reinforced concrete slabs with varying depth, span and support conditions. The results aim to provide insight to facilitate the development of more accurate simplified methods for determining the direct shear response of blast loaded reinforced concrete members, such as the single degree of freedom method. © 2014 Elsevier Ltd.
Dragos, J, Visintin, P, Wu, C & Oehlers, DJ 2014, 'A Numerically Efficient Finite Element Analysis of Reinforced Concrete Members Subjected to Blasts', International Journal of Protective Structures, vol. 5, no. 1, pp. 65-82.
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A common approach for predicting member response under blast loading is through the use of a finite element software package. Such an analysis typically requires the implementation of a three dimensional mesh and, therefore, requires significant computational effort. In this paper, it is shown how a displacement based segmental moment-rotation (M/θ) analysis can be used to simulate the cracking and softening behavior of reinforced concrete over a segment of a member using the mechanics of partial interaction and shear friction. It is then shown how the M/θ behavior extracted from the segmental analysis can be simplified into an equivalent one dimensional moment curvature relationship which can then be incorporated into a fast running one dimensional finite element approach to determine the response of reinforced concrete slabs subjected to blast loading. Then, results determined using the approach are compared against those obtained from blast experiments and the numerical efficiency of the model is discussed.
Fatahi, B & Tabatabaiefar, SHR 2014, 'Effects of Soil Plasticity on Seismic Performance of Mid-Rise Building Frames Resting on Soft Soils', Advances in Structural Engineering, vol. 17, no. 10, pp. 1387-1402.
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In this study, the effects of Plasticity Index (PI) variation on the seismic response of mid-rise building frames resting on soft soil deposits are investigated. To achieve this goal, three structural models including 5, 10, and 15 storey buildings are simulated in conjunction with a clayey soil representing soil class Eeaccording to the classification of AS1170.4–2007 (Earthquake actions in Australia) and then varying the Plasticity Index. Structural sections of the selected frames were designed according to AS3600–2009 (Australian Standard for Concrete Structures) after undertaking dynamic analysis under the influence of four different earthquake ground motions. The frame sections are modelled and analysed, employing finite difference method adopting FLAC 2D software under two different boundary conditions: (i) fixed base (no Soil-Structure Interaction), and (ii) flexible base considering soil-structure interaction. Fully nonlinear dynamic analyses under the influence of different earthquake records are conducted and the results in terms of maximum lateral displacements and inter-storey drifts for the above mentioned boundary conditions are obtained, compared, and discussed. Base on the results of the numerical investigations, it becomes apparent that as the Plasticity Index of the subsoil increases, the base shears of mid-rise building frames resting on soft soil deposits increase, while the lateral deflections and corresponding inter-storey drifts decrease. It is concluded that reduction of the Plasticity Index could noticeably amplify the effects of soil-structure interaction on the seismic response of mid-rise building frames.
Fatahi, B & Tabatabaiefar, SHR 2014, 'Fully Nonlinear versus Equivalent Linear Computation Method for Seismic Analysis of Midrise Buildings on Soft Soils', International Journal of Geomechanics, vol. 14, no. 4, pp. 04014016-04014016.
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In this study, the accuracy of a fully nonlinear method against an equivalent linear method for dynamic analysis of soil-structure interaction is investigated comparing the predicted results of both numerical procedures. Three structural models, including 5-story, 10-story, and 15-story buildings, are simulated in conjunction with two soil types with shear-wave velocities less than 600?m/s. The aforementioned frames were analyzed under three different conditions: (1) fixed-base model performing conventional time history dynamic analysis under the influence of earthquake records, (2) flexible-base model (considering full soil-structure interaction) conducting equivalent linear dynamic analysis of soil-structure interaction under seismic loads, and (3) flexible-base model performing fully nonlinear dynamic analysis of soil-structure interaction under the influence of earthquake records. The results of these three cases in terms of average lateral story deflections and interstory drifts are determined, compared, and discussed. It is concluded that the equivalent linear method of the dynamic analysis underestimates the inelastic seismic response of midrise moment resisting building frames resting on soft soils in comparison with the fully nonlinear dynamic analysis method. Therefore, a design procedure using the equivalent linear method cannot adequately guarantee the structural safety for midrise building frames resting on soft soils.
Fatahi, B, Basack, S, Ryan, P, Zhou, W-H & Khabbaz, H 2014, 'Performance of laterally loaded piles considering soil and interface parameters', GEOMECHANICS AND ENGINEERING, vol. 7, no. 5, pp. 495-524.
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© 2014 Techno-Press, Ltd. To investigate the soil-pile interactive performance under lateral loads, a set of laboratory model tests was conducted on remoulded test bed of soft clay and medium dense sand. Then, a simplified boundary element analysis had been carried out assuming floating pile. In case of soft clay, it has been observed that lateral loads on piles can initiate the formation of a gap, soil heave and the tension crack in the vicinity of the soil surface and the interface, whereas in medium dense sand, a semi-elliptical depression zone can develop. Comparison of test and boundary element results indicates the accuracy of the solution developed. However, in the boundary element analysis, the possible shear stresses likely to be developed at the interface are ignored in order to simplify the existing complex equations. Moreover, it is unable to capture the influence of base restraint in case of a socketed pile. To bridge up this gap and to study the influence of the initial stress state and interface parameters, a field based case-study of laterally-loaded pile in layered soil with socketed tip is explored and modelled using the finite element method. The results of the model have been verified against known field measurements from a case-study. Parametric studies have been conducted to investigate the influence of the coefficient of lateral earth pressure and the interface strength reduction factor on the results of the model.
Fatahi, B, Khabbaz, H & Indraratna, B 2014, 'Modelling of unsaturated ground behaviour influenced by vegetation transpiration', Geomechanics and Geoengineering, vol. 9, no. 3, pp. 187-207.
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Vegetation contributes to weak soil stabilisation through reinforcement of the soil, dissipation of excess pore pressure and increasing the shear strength by induced matric suction. This paper describes the way vegetation influences soil matric suction, shrinkage and ground settlement in the vadose zone through transpiration. A mathematical model for the rate of root water uptake, including the root growth rate considering ground conditions, type of vegetation and climatic parameters, has been developed. A finite element approach is employed to solve the transient coupled flow-deformation equations. The finite element mesh is built using partially saturated soil elements capable of representing the salient aspects of unsaturated permeability and the soil water characteristic curve. The model formulation is based on the effective stress theory of unsaturated soils. Based on this proposed model, the distribution of the ground matric suction profile adjacent to the tree is numerically analysed. Current field measurements of soil matric suction and moisture content collected from Miram site located in Victoria State, Australia by the authors are compared with the numerical predictions. The results indicate that the proposed root water uptake model incorporated in the numerical analysis can be used for prediction of ground properties influenced by tree roots. © 2014 Taylor & Francis.
Fatahi, B, Tabatabaiefar, SHR & Samali, B 2014, 'Soil-structure interaction vs Site effect for seismic design of tall buildings on soft soil', GEOMECHANICS AND ENGINEERING, vol. 6, no. 3, pp. 293-320.
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In this study, in order to evaluate adequacy of considering local site effect, excluding soil-structure interaction (SSI) effects in inelastic dynamic analysis and design of mid-rise moment resisting building frames, three structural models including 5, 10, and 15 storey buildings are simulated in conjunction with two soil types with the shear wave velocities less than 600 m/s, representing soil classes De and Ee according to the classification of AS1170.4-2007 (Earthquake actions in Australia) having 30 m bedrock depth. Structural sections of the selected frames were designed according to AS3600:2009 (Australian Standard for Concrete Structures) after undertaking inelastic dynamic analysis under the influence of four different earthquake ground motions. Then the above mentioned frames were analysed under three different boundary conditions: (i) fixed base under direct influence of earthquake records; (ii) fixed base considering local site effect modifying the earthquake record only; and (iii) flexible-base (considering full soil-structure interaction). The results of the analyses in terms of base shears and structural drifts for the above mentioned boundary conditions are compared and discussed. It is concluded that the conventional inelastic design procedure by only including the local site effect excluding SSI cannot adequately guarantee the structural safety for mid-rise moment resisting buildings higher than 5 storeys resting on soft soil deposits.
Forsythe, P & Ding, G 2014, 'Greenhouse Gas Emissions from Excavation on Residential Construction Sites', Construction Economics and Building, vol. 14, no. 4, pp. 1-10.
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Despite considerable research concerning the manifestation of greenhouse gases in the usage of buildings, little has been done concerning emissions arising from the construction process itself. This paper specifically examines emissions arising from cut and fill excavation on residential construction sites. Even though such excavation is often seen as being economical in terms of providing a flat base for concrete raft slab construction, the environmental consequences of this approach need to be considered more fully in terms of impact on the environment. This is particularly important when steeply sloping sites are involved and for different soil types. The paper undertakes a study that quantitatively assesses the cumulative greenhouse gas emissions caused by cut and fill excavation on 52 residential projects in Australia for a range of slope and soil types. The paper presents results from the study and concludes that greenhouse gas emissions increase as site slope increases; the building footprint area (as distinct from Gross Floor Area), exposes the need to reduce the area of the building to reduce greenhouse gas emissions; excavation of rock soils creates higher emissions than other soil types; and cut and fill excavation on steeply slope sites increase emissions. Potential alternative construction includes suspended floor construction systems which involve less excavation.
Fukumoto, T, Thomas, PS, Simon, P, Dubaj, T & Stuart, BH 2014, 'Estimation of the curing rate of acrylamide used as a consolidant in heritage sandstone conservation', JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, vol. 116, no. 2, pp. 619-624.
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Ha, QP, That, ND, Nam, PT & Trinh, H 2014, 'Partial state estimation for linear systems with output and input time delays', ISA TRANSACTIONS, vol. 53, no. 2, pp. 327-334.
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This paper deals with the problem of partial state observer design for linear systems that are subject to time delays in the measured output as well as the control input. By choosing a set of appropriate augmented LyapunovKrasovskii functionals with a triple-integral term and using the information of both the delayed output and input, a novel approach to design a minimal-order observer is proposed to guarantee that the observer error is e-convergent with an exponential rate. Existence conditions of such an observer are derived in terms of matrix inequalities for the cases with time delays in both the output and input and with output delay only. Constructive design algorithms are introduced. Numerical examples are provided to illustrate the design procedure, practicality and effectiveness of the proposed observer.
Ho, L, Fatahi, B & Khabbaz, H 2014, 'Analytical solution for one-dimensional consolidation of unsaturated soils using eigenfunction expansion method', INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, vol. 38, no. 10, pp. 1058-1077.
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This paper introduces an exact analytical solution for governing flow equations for one-dimensional consolidation in unsaturated soil stratum using the techniques of eigenfunction expansion and Laplace transformation. The homogeneous boundary conditions adopted in this study are as follows: (i) a one-way drainage system of homogenous soils, in which the top surface is considered as permeable to air and water, whereas the base is an impervious bedrock; and (ii) a two-way drainage system where both soil ends allow free dissipation of pore-air and pore-water pressures. In addition, the analytical development adopts initial conditions capturing both uniform and linear distributions of the initial excess pore pressures within the soil stratum. Eigenfunctions and eigenvalues are parts of the general solution and can be obtained based on the proposed boundary conditions. Besides, the Laplace transform method is adopted to solve the first-order differential equations. Once equations with transformed domain are all obtained, the final solutions, which are proposed to be functions of time and depth, can be achieved by taking an inverse Laplace transform. To verify the proposed solution, two worked examples are provided to present the consolidation characteristics of unsaturated soils based on the proposed method. The validation of the recent results against other existing analytical solutions is graphically demonstrated. © 2013 John Wiley & Sons, Ltd.
Hokmabadi, AS, Fatahi, B & Samali, B 2014, 'Assessment of soil-pile-structure interaction influencing seismic response of mid-rise buildings sitting on floating pile foundations', COMPUTERS AND GEOTECHNICS, vol. 55, no. 1, pp. 172-186.
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The role of the seismic soil-pile-structure interaction (SSPSI) is usually considered beneficial to the structural system under seismic loading since it lengthens the lateral fundamental period and leads to higher damping of the system in comparison with the fixed-base assumption. Lessons learned from recent earthquakes show that fixed-base assumption could be misleading, and neglecting the influence of SSPSI could lead to unsafe design particularly for structures founded on soft soils. In this study, in order to better understand the SSPSI phenomena, a series of shaking table tests have been conducted for three different cases, namely: (i) fixed-base structure representing the situation excluding the soil-structure interaction; (ii) structure supported by shallow foundation on soft soil; and (iii) structure supported by floating (frictional) pile foundation in soft soil. A laminar soil container has been designed and constructed to simulate the free field soil response by minimising boundary effects during shaking table tests. In addition, a fully nonlinear three dimensional numerical model employing FLAC3D has been adopted to perform time-history analysis on the mentioned three cases. The numerical model adopts hysteretic damping algorithm representing the variation of the shear modulus and damping ratio of the soil with the cyclic shear strain capturing the energy absorbing characteristics of the soil. Results are presented in terms of the structural response parameters most significant for the damage such as foundation rocking, base shear, floor deformation, and inter-storey drifts. Comparison of the numerical predictions and the experimental data shows a good agreement confirming the reliability of the numerical model. Both experimental and numerical results indicate that soil-structure interaction amplifies the lateral deflections and inter-storey drifts of the structures supported by floating pile foundations in comparison to the fixed base struc...
Indraratna, B, Navaratnarajah, SK, Nimbalkar, S & Rujikiatkamjorn, C 2014, 'Use of shock mats for enhanced stability of railroad track foundation', Australian Geomechanics Journal, vol. 49, no. 4, pp. 101-111.
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Increasing demand for High Speed Rail (HSR) and fast heavy haul poses a serious challenge for stability of tracks on problematic ground. Ballast is a key track foundation material placed underneath the sleepers which provides structural support against high cyclic and impact stresses caused by moving trains. Degradation of ballast contributes to a large percentage of track maintenance costs apart from affecting longevity and stability. In recent years, use of elastometric soft pads underneath sleepers has become increasingly popular as means of reducing track damage. The 'shock mat' placed under the sleeper is traditionally called Under Sleeper Pad (USP), and when it is placed under ballast, the term Under Ballast Mat (UBM) is often used. Currently there is lack of comprehensive assessment on the geotechnical behaviour of ballast using these artificial inclusions under impact and cyclic loading. In this study, a series of largescale laboratory tests were conducted to understand the performance of these energy absorbing 'shock mats' in the attenuation of impact and cyclic stresses and subsequent mitigation of ballast degradation. Impact loads were simulated using a high-capacity drop-weight impact testing equipment, while the cyclic loads were simulated using a large-scale prismoidal process simulation test apparatus. This paper presents a state-of-the-art review of laboratory studies and field trials demonstrating the benefits of USPs and UBMs in rail industry.
Indraratna, B, Nimbalkar, S & Neville, T 2014, 'Performance assessment of reinforced ballasted rail track', Proceedings of the Institution of Civil Engineers - Ground Improvement, vol. 167, no. 1, pp. 24-34.
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In coastal Australia, high population density and increased traffic volumes have promoted rapid expansion of urban transportation infrastructure including railways. Coastal soft clays pose significant construction challenges. Therefore, the search for innovative ground improvement techniques imperative for more resilient and sustainable transport infrastructure has become an obvious priority in research and development. Use of artificial inclusions such as polymeric geosynthetics and energy-absorbing shock mats is described in this paper as a suitable alternative for reducing unacceptable track degradation and for ensuring sustainable track alignment. An extensive monitoring programme was undertaken on fully instrumented track sections constructed near Singleton, New South Wales, Australia. Four types of geosynthetics were installed at the ballast–capping interface of track sections located on different types of subgrades. It was found that geogrids could decrease the vertical settlement of the ballast layer with the obvious benefits of improved track stability and decreased cost of maintenance. It was also found that the effectiveness of reinforcing geogrids is greater when the subgrade is soft.
Indraratna, B, Nimbalkar, S & Rujikiatkamjorn, C 2014, 'Enhancement of rail track performance through utilisation of geosynthetic inclusions', Geotechnical Engineering, vol. 45, no. 1, pp. 17-27.
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In coastal regions of Australia, high population density and increased traffic volumes have led to rapid expansion of rail transport. Use of artificial inclusions such as polymeric geosynthetics for enhanced soil-structure interaction and rubber shock mats for absorbing energy with the aim of reducing particle breakage is described in this paper as a cost-effective option. This paper highlights the results of a laboratory study on the deformation of coal fouled ballast stabilised with geogrids, at various degrees of fouling. A novel Track Process Simulation Apparatus (TPSA) was employed to reproduce realistic rail track conditions under cyclic loading, and the Void contaminant index (VCI) was used to assess the level of ballast fouling. The beneficial aspects of the geogrid inclusion are discussed in the paper. Laboratory results showed that biaxial geogrids can reduce the deformation of fresh ballast, but their effectiveness diminishes with an increase of VCI. A threshold value of VCI was proposed in view of track maintenance. Comprehensive field trials were executed on two fullscale rail tracks in the towns of Bulli and Singleton in New South Wales. These trials facilitated the evaluation of the relative performance of different types of geogrids, geocomposites and shock mats installed in fully instrumented track sections. Field trials showed that the use of recycled ballasted in rail tracks was a feasible and effective alternative. The performance of geogrids and geocomposite was found to be associated with their geometrical and mechanical properties as well as with the type of subgrade. The distributions of vertical and lateral stresses in the track were also assessed. In addition, effects of magnitude of axle load and train speed on stress distributions were studied. Copyright © 2014 Southeast Asian Geotechnical Society (SEAGS). All Rights Reserved.
Indraratna, B, Nimbalkar, S & Rujikiatkamjorn, C 2014, 'From theory to practice in track geomechanics – Australian perspective for synthetic inclusions', Transportation Geotechnics, vol. 1, no. 4, pp. 171-187.
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© 2014 Elsevier Ltd. The adoption of heavier axle loads and high speed rails have posed serious geotechnical issues with ballasted railway tracks. These issues include poor drainage of soft coastal soils, ballast degradation under cyclic and impact loads, differential settlement of track and misalignment due to lateral movements, and inadequate bearing capacity of some compacted ballast. The mechanisms of ballast degradation and deformation, the need for effective track confinement, understanding of interface behaviour, determining dynamic bearing capacity and use of energy absorbing shock mats and synthetic grids require further insight to improve the existing design guidelines for future high speed commuter and heavier freight trains. In this paper, the current state-of-the-art knowledge of rail track geomechanics is discussed, with particular emphasis on the effects of geosynthetic applications on ballast degradation, and track performance. The stress-strain response and volumetric changes of ballast stabilised with geosynthetics observed in the laboratory experiments were captured through discrete element and finite element models. Installing shock mats and geosynthetics in the track substructure led to the attenuation of high cyclic and impact forces, thereby mitigating ballast degradation. Comprehensive field studies on instrumented tracks at Bulli (near Wollongong) and Singleton (near Newcastle) supported by Sydney Trains and ARTC, were carried out to measure the in situ stresses and deformation of ballast embankments. The paper focuses primarily on research conducted at University of Wollongong for enhanced track performance, highlighting some examples of innovation from theory to practice.
Indraratna, B, Nimbalkar, S & Rujikiatkamjorn, C 2014, 'Preface', Transportation Geotechnics, vol. 1, no. 4, pp. 145-146.
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Indraratna, B, Nimbalkar, S, Coop, M & Sloan, SW 2014, 'A constitutive model for coal-fouled ballast capturing the effects of particle degradation', Computers and Geotechnics, vol. 61, pp. 96-107.
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Rail tracks undergo degradation owing to particle breakage and fouling of ballast by various fines including coal and subgrade soil. As the ballast becomes fouled, its strength and drainage capacity are compromised, sometimes resulting in differential settlement and reduced track stability. This paper demonstrates a continuum mechanics based framework to evaluate the detrimental effect of fines on the strength, deformation and degradation of coal-fouled ballast under monotonic loading. An elastoplastic constitutive model that considers the effect of fines content and energy consumption associated with particle breakage during shearing is presented. This multiphase constitutive model is developed within a critical state framework based on a kinematic-type yield locus and a modified stress-dilatancy approach. A general formulation for the rate of ballast breakage and coal particle breakage during triaxial shearing is presented and incorporated into the plastic flow rule to accurately predict the stress-strain response of coal-fouled ballast at various confining pressures. The behaviour of ballast at various levels of fouling is analysed and validated by experimental data. © 2014 Elsevier Ltd.
Jiang, X, Li, Y, Li, J, Wang, J & Yao, J 2014, 'Piezoelectric energy harvesting from traffic-induced pavement vibrations', JOURNAL OF RENEWABLE AND SUSTAINABLE ENERGY, vol. 6, no. 4.
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This paper focuses on the development and experimental testing of a potential clean energy source for powering the remote equipment used in transportation infrastructure. Traditional power sources (i.e., power cables and batteries) are excessively expensive or infeasible in this type of application. A compression-based roadway energy harvester has been developed that can be embedded into pavement to scavenge electrical energy from traffic-induced vibrations. The proposed roadway harvester employs a group of piezoelectric harvesting units to convert traffic-induced vibrations into electrical energy, and each single harvesting unit contains three piezoelectric multilayer stacks. According to the linear theory of piezoelasticity, a two-degree-of-freedom electromechanical model of the piezoelectric harvesting unit was developed to characterize its performance in generating electrical energy under external excitations. Experimental testing in the laboratory was conducted to investigate the output power properties of the harvesting unit and shows good agreement with the theoretical analysis. Based on the testing results of the harvesting unit, the capability of the proposed roadway harvester has been theoretically evaluated and demonstrated that it has the ability to generate sufficient energy for driving common electrical equipment used in transportation infrastructure. © 2014 AIP Publishing LLC.
Jiang, X, Wang, J, Li, Y & Li, J 2014, 'Design and modelling of a novel linear electromagnetic vibration energy harvester', INTERNATIONAL JOURNAL OF APPLIED ELECTROMAGNETICS AND MECHANICS, vol. 46, no. 1, pp. 165-183.
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This paper presents the design and evaluation of a novel permanent magnet (PM) energy harvesting system for scavenging electrical energy from ambient vibrations. A two-phase tubular linear PM vibration energy harvester consisting of a mover attached with permanent magnets and a slotted stator with built-in two-phase electromagnetic coils is proposed to convert vibrational kinetic energy into electrical energy. Aiming at maximizing the efficiency of vibration-to-electrical energy conversion under designated vibration and limited space requirement, a systematic research, including innovative device design, theoretical modelling and analysis, and finite element evaluation on the PM vibration energy harvester will be presented in this paper. In addition, the methodology of winding the two-phase coils in slotted stator is explicated in order to fully utilize the harvested electrical energy. A two-phase rectifier circuit is developed to convert the alternative voltage generated by the PM harvester into DC voltage that can be used directly by the external resistive load. Simulation results indicate that the proposed linear PM vibration energy harvesting system is able to generate about 100 watt DC electrical power under the vibration with the velocity of 0.4 m/s and the output electrical power is proportional to the levels of vibration excitations.
Jiang, XZ, Li, YC, Wang, J & Li, JC 2014, 'Electromechanical modeling and experimental analysis of a compression-based piezoelectric vibration energy harvester', International Journal of Smart and Nano Materials, vol. 5, no. 3, pp. 152-168.
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Over the past few decades, wireless sensor networks have been widely used in the field of structure health monitoring of civil, mechanical, and aerospace systems. Currently, most wireless sensor networks are battery-powered and it is costly and unsustainable for maintenance because of the requirement for frequent battery replacements. As an attempt to address such issue, this article theoretically and experimentally studies a compression-based piezoelectric energy harvester using a multilayer stack configuration, which is suitable for civil infrastructure system applications where large compressive loads occur, such as heavily vehicular loading acting on pavements. In this article, we firstly present analytical and numerical modeling of the piezoelectric multilayer stack under axial compressive loading, which is based on the linear theory of piezoelectricity. A two-degree-of-freedom electromechanical model, considering both the mechanical and electrical aspects of the proposed harvester, was developed to characterize the harvested electrical power under the external electrical load. Exact closed-form expressions of the electromechanical models have been derived to analyze the mechanical and electrical properties of the proposed harvester. The theoretical analyses are validated through several experiments for a test prototype under harmonic excitations. The test results exhibit very good agreement with the analytical analyses and numerical simulations for a range of resistive loads and input excitation levels. © 2014 The Author(s).
Khabbaz, H & Fatahi, B 2014, 'How to overcome geotechnical challenges in implementing high speed rail systems in Australia', Geotechnical Engineering, vol. 45, no. 1, pp. 39-47.
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Although there are a few medium speed rail systems in Australia, there is not a passenger rail transport with the high transit speed, seen in other countries. This paper firstly summarises lessons learnt from other countries, experienced high speed rail (HRS) for many years. Then, the challenges associated with implementing HSR systems in Australia are explained. The main challenges include selection and design of proper tracks, geographical issues, environmental concerns, economics and project costs and construction procedures. The second part of the paper presents the effective solutions to the geotechnical challenges associated with HSR systems. Various approaches are presented to improve the ballast layer properties and enhance the track formation bearing strength, stiffness, resiliency and dynamic properties. Employing concrete slab (ballast-less) tracks is also taken into consideration for HSR systems, and their performance is compared to ballasted tracks. Copyright © 2014 Southeast Asian Geotechnical Society (SEAGS). All Rights Reserved.
Khorsandnia, N, Schaenzlin, J, Valipour, H & Crews, K 2014, 'Time-dependent behaviour of timber-concrete composite members: Numerical verification, sensitivity and influence of material properties', CONSTRUCTION AND BUILDING MATERIALS, vol. 66, pp. 192-208.
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Khorsandnia, N, Valipour, H & Crews, K 2014, 'Structural Response of Timber-Concrete Composite Beams Predicted by Finite Element Models and Manual Calculations', ADVANCES IN STRUCTURAL ENGINEERING, vol. 17, no. 11, pp. 1601-1621.
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This paper presents the structural response of timber-concrete composite (TCC) beams predicted by finite element models (i.e. continuum-based and 1D frame) and manual calculations. Details of constitutive laws adopted for modelling timber and concrete are provided and application of the Hashin damage model in conjunction with continuum-based FE for capturing failure of timber under bi-axial stress state is discussed. A simplified strategy for modelling the TCC connection is proposed in which the connection is modelled by a nonlinear spring and the full load-slip behaviour of each TCC connection is expressed with a formula that can be directly implemented in the general purpose FE codes and used for nonlinear analysis of TCC beams. The developed FE models are verified by examples taken from the literature. Furthermore, the load-displacement response and ultimate loading capacity of the TCC beams are determined according to Eurocode 5 method and compared with FE model predictions.
Khorsandnia, N, Valipour, H, Foster, S & Crews, K 2014, 'A force-based frame finite element formulation for analysis of two- and three-layered composite beams with material non-linearity', INTERNATIONAL JOURNAL OF NON-LINEAR MECHANICS, vol. 62, pp. 12-22.
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Khorsandnia, N, Valipour, HR & Crews, K 2014, 'Nonlinear Long-Term Analysis of Timber-Concrete Composite Structures with Finite Element-Finite Difference Scheme', Applied Mechanics and Materials, vol. 553, pp. 618-624.
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Long-term analysis of timber-concrete composite (TCC) structures is a challenging task owing to the time-dependent behaviour of timber, concrete and connections which are highly nonlinear under variable environmental conditions (i.e. temperature, humidity). In this paper an efficient numerical method that takes advantage of a finite element-finite difference (FE-FD) scheme is presented. The differential equations governing the long-term behaviour of TCC section under variable humidity are solved using the FD scheme and the differential equations governing the mechanical behaviour of the composite beam are solved by a FE formulation recast in the framework of force-interpolation concept. The comparison between experimental data and numerical results shows the sufficient accuracy of the proposed FE-FD model for capturing long-term behaviour of TCC members.
Li, J & Hao, H 2014, 'A Simplified Numerical Method for Blast Induced Structural Response Analysis', International Journal of Protective Structures, vol. 5, no. 3, pp. 323-348.
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Efficiently and accurately predicting structural dynamic response and damage to external blast loading is a big challenge to both structural engineers and researchers. The conventional numerical treatment to this problem is proved being able to give reliable predictions, however at the cost of enormous computational time and resource. Simplified SDOF approach is popularly used in design as it is straightforward to use and also gives good structural response predictions if the response is governed by a global response mode (shear or bending) and the accurate dynamic deflection curve is available, but it cannot predict the detailed local structural damage. In this study, a new numerical approach that combines the recently proposed two-step method and the static condensation method is proposed to analyze structure response and collapse to blast loads. The two-step method divides the structural response into two phases, i.e. forced vibration phase (blast loading duration) and free vibration phase. Single- Degree-of-Freedom system approach is adopted to solve the structural element responses at the end of the forced vibration phase, and the structural free vibration simulation is carried out using the hydro-code LS-DYNA to calculate the detailed structural response and damage. The static condensation technique is utilized to condense structural components that are relatively away from the explosion center to further reduce the computational effort. To demonstrate the proposed method, the structural responses of a three story RC frame to blast loads are calculated by four approaches, i.e. the traditional detailed FE simulation, the two-step method, the model condensation method, and the new combined two-step and dynamic condensation method. Through the results comparison, the efficiency and accuracy of the proposed combined approach are demonstrated.
Li, J & Hao, H 2014, 'Numerical and Theoretical Study of Concrete Spall Damage under Blast Loads', Applied Mechanics and Materials, vol. 553, pp. 774-779.
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Spall damage is a typical failure mode of concrete structures under blast or high velocity impact loads. At the opposite side from which the structural element was impulsively loaded, spall will occur if the net primary stresses over an area exceed the dynamic tensile strength of concrete. Fragments of structural element could eject with large velocities, and this kind of damage can cause severe threats to equipment and personnel. In the present study, reinforced concrete columns subjected to the blast loading is investigated and the numerical study of concrete spall is conducted. The spall depth is recorded and compared with the theoretical results derived from wave propagation theory. The parameters that affect the concrete spall damage are investigated.
Li, J & Hao, H 2014, 'Numerical study of concrete spall damage to blast loads', International Journal of Impact Engineering, vol. 68, pp. 41-55.
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Spall damage is a typical damage mode of concrete structures under blast or high velocity impact loads. Blast and impact loads generate a stress wave propagating in the structure. At the opposite side from which the structural element is impulsively loaded, spall will occur if the net primary stresses over an area exceed the concrete dynamic tensile strength and the resistance force such as the material dynamic bond and interlock. Fragments of structural element generated from spall damage could eject with large velocities, and impose significant threats to equipment and personnel even it does not necessarily greatly reduce the load carrying capacity of the structural components. In the present study, spall damage of generic reinforced concrete columns subjected to blast loads is investigated numerically. Three-dimensional numerical models are developed to predict the concrete spalling under blast loads. The accuracy of the numerical simulations is verified with blast testing data reported by other researchers. Intensive numerical simulations are then carried out to investigate the influences of the column dimensions and reinforcement mesh on concrete spall damage. Based on numerical simulation data, empirical relations are suggested to predict concrete spall damage based on explosion scenarios, column dimensions and reinforcement conditions. © 2014 Elsevier Ltd. All rights reserved.
Li, Y & Jack Wang, J 2014, 'A Pedestrian Navigation System Based on Low Cost IMU', Journal of Navigation, vol. 67, no. 6, pp. 929-949.
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For indoor pedestrian navigation with a shoe-mounted inertial measurement unit (IMU), the zero velocity update (ZUPT) technique is implemented to constrain the sensors' error. ZUPT uses the fact that a stance phase appears in each step at zero velocity to correct IMU errors periodically. This paper introduces three main contributions we have achieved based on ZUPT. Since correct stance phase detection is critical for the success of applying ZUPT, we have developed a new approach to detect the stance phase of different gait styles, including walking, running and stair climbing. As the extension of ZUPT, we have proposed a new concept called constant velocity update (CUPT) to correct IMU errors on a moving platform with constant velocity, such as elevators or escalators where ZUPT is infeasible. A closed-loop step-wise smoothing algorithm has also been developed to eliminate discontinuities in the trajectory caused by sharp corrections. Experimental results demonstrate the effectiveness of the proposed algorithms.
Li, Y & Li, J 2014, 'Dynamic characteristics of a magnetorheological pin joint for civil structures', Frontiers of Mechanical Engineering, vol. 9, no. 1, pp. 15-33.
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Magnetorheological (MR) pin joint is a novel device in which its joint moment resistance can be controlled in real-time by altering the applied magnetic field. The smart pin joint is intended to be used as a controllable connector between the columns and beams of a civil structure to instantaneously shift the structural natural frequencies in order to avoid resonance and therefore to reduce unwanted vibrations and hence prevent structural damage. As an intrinsically nonlinear device, modelling of this MR fluid based device is a challenging task and makes the design of a suitable control algorithm a cumbersome situation. Aimed at its application in civil structure, the main purpose of this paper is to test and characterise the hysteretic behaviour of MR pin joint. A test scheme is designed to obtain the dynamic performance of MR pin joint in the dominant earthquake frequency range. Some unique phenomena different from those of MR damper are observed through the experimental testing. A computationally-efficient model is proposed by introducing a hyperbolic element to accurately reproduce its dynamic behaviour and to further facilitate the design of a suitable control algorithm. Comprehensive investigations on the model accuracy and dependences of the proposed model on loading condition (frequency and amplitude) and input current level are reported in the last section of this paper. © 2014 Higher Education Press and Springer-Verlag Berlin Heidelberg.
Li, Y, Li, J, Li, W & Du, H 2014, 'A state-of-the-art review on magnetorheological elastomer devices', SMART MATERIALS AND STRUCTURES, vol. 23, no. 12.
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© 2014 IOP Publishing Ltd. During the last few decades, magnetorheological (MR) elastomers have attracted a significant amount of attention for their enormous potential in engineering applications. Because they are a solid counterpart to MR fluids, MR elastomers exhibit a unique field-dependent material property when exposed to a magnetic field, and they overcome major issues faced in magnetorheological fluids, e.g. the deposition of iron particles, sealing problems and environmental contamination. Such advantages offer great potential for designing intelligent devices to be used in various engineering fields, especially in fields that involve vibration reduction and isolation. This paper presents a state of the art review on the recent progress of MR elastomer technology, with special emphasis on the research and development of MR elastomer devices and their applications. To keep the integrity of the knowledge, this review includes a brief introduction of MR elastomer materials and follows with a discussion of critical issues involved in designing magnetorheological elastomer devices, i.e. operation modes, coil placements and principle fundamentals. A comprehensive review has been presented on the research and development of MR elastomer devices, including vibration absorbers, vibration isolators, base isolators, sensing devices, and so on. A summary of the research on the modeling mechanical behavior for both the material and the devices is presented. Finally, the challenges and the potential facing magnetorheological elastomer technology are discussed, and suggestions have been made based on the authors' knowledge and experience.
Li, Y, Li, J, Tian, T & Li, W 2014, 'A highly adjustable magnetorheological elastomer base isolator for applications of real-time adaptive control (vol 22, 095020, 2013)', SMART MATERIALS AND STRUCTURES, vol. 23, no. 12.
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Ma, JL, Wu, CQ, Zhi, XD & Fan, F 2014, 'Prediction of Confined Blast Loading in Single-Layer Lattice Shells', Advances in Structural Engineering, vol. 17, no. 7, pp. 1029-1043.
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Single-layer lattice shells (also known as gridshells) are widely used for architecturally innovative structures. When an explosion occurs inside such a structure, confined blast loading on the structural components will be seriously affected by different factors, such as charge locations and weight, structural types and forms. Moreover, slight changes of blast loading perhaps result in various responses for such a complicated structure. In this paper, blast loads on single-layer lattice shell are calculated by AUTODYN software package. The effect of scaled distance, ratio of rise to span and ratio of height to span are investigated. Simplification of blast loading is studied, and the principles of equivalent loading process are validated with a 40 meters single-layer Kiewitt-8 reticulated dome. In order to predict the blast loading, a precise and simple model is derived from numerical results, which is suitable for a wide scope of single-layer lattice shells. Two applications with different charge weight, structural spans and forms are worked out by using the blast prediction model. Good agreements of comparisons are achieved between prediction model and numerical results.
Mansoury, B & Tabatabaiefar, HR 2014, 'Application Of Sustainable Design Principles To Increase Energy Efficiency Of Existing Buildings', Building Research Journal, vol. 61, no. 3, pp. 167-177.
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AbstractThis study investigates the effectiveness of different energy retrofitting techniques and examines the impact of employing those methods on energy consumption of existing residential buildings. Based on the research findings, the most effective and practical method of retrofitting has been proposed in order to improve energy efficiency of existing buildings. In order to achieve this goal, an existing residential building has been simulated in FirstRate 5 software so as to determine the existing thermal performance of the building. Afterwards, considering sustainable design principles, different insulation layers, glazing, and construction materials have been employed to conduct a comprehensive thermal performance study. Based on the research outcomes, the best technique for increasing energy efficiency of existing buildings and reducing their environmental impact and footprint has been identified and proposed for practical purposes.
Mohammadi, I, Khabbaz, H & Vessalas, K 2014, 'In-depth assessment of Crumb Rubber Concrete (CRC) prepared by water-soaking treatment method for rigid pavements', CONSTRUCTION AND BUILDING MATERIALS, vol. 71, pp. 456-471.
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© 2014 Elsevier Ltd. All rights reserved. This paper investigates effects of applying an innovative method of rubber treatment, named water-soaking, on fresh and hardened properties of rubberised concrete. Unlike the current methods of introducing rubber into concrete mixtures, which are conducted in a dry process, this research trialled introducing of rubber particles into the mixture in a wet process. Conducting the required sets of fresh and hardened concrete tests, mixtures with a variety of rubber content and water-cement ratios were evaluated. In order to measure the effectiveness of the introduced method, properties of concrete prepared by water soaking-method were compared with concrete containing untreated rubber. It was observed that applying the proposed method resulted in improvement of fresh and hardened properties. It resulted in more uniform distribution of rubber particles in concrete matrix, less entrapped air in concrete mixture and 22% higher compressive strength for rubberised concrete.
Mohottige, NW, Wu, C & Hao, H 2014, 'Characteristics of Free Air Blast Loading Due to Simultaneously Detonated Multiple Charges', International Journal of Structural Stability and Dynamics, vol. 14, no. 04, pp. 1450002-1450002.
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Extensive research has been conducted to investigate the characteristics of blast load due to single charge explosion, including numerical simulations and experimental blast tests in both unconfined and confined environments. Further, available guidelines for blast resistant design such as UFC-3-340-02 (2008) and ASCE 59-11 (2011) provide details to predict blast loads on a structure subjected to single charge explosion. However, blast load characteristics due to multiple charge explosions are poorly discussed in available literature. In this paper, commercially available Hydrocode, AUTODYN is calibrated for single charge explosions. Based on a comparison between numerical simulation and UFC prediction, correction factors for peak reflected pressure and positive reflected impulse as a function of charge weight, scaled distance and mesh size of the numerical model are proposed to minimize the errors in simulations. The calibrated AUTODYN model is then used to conduct parametric studies to investigate the effects of charge weight, scaled distance, number of charges and distance between the charges on the characteristics of free air blast load due to simultaneous detonated multiple charges. Numerical simulation results are used to derive analytical formulas for predictions of peak reflected pressure ratio and positive reflected impulse ratio between single and multiple explosions. The discussion is made on characteristics of free air blast load due to simultaneous detonated multiple charges.
Mustapha, S, Lu, Y, Li, J & Ye, L 2014, 'Damage detection in rebar-reinforced concrete beams based on time reversal of guided waves', Structural Health Monitoring, vol. 13, no. 4, pp. 347-358.
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The propagation properties of ultrasonic waves in rebar-reinforced concrete beams were investigated and their ability for damage identification was demonstrated. Rectangular piezoelectric ceramics were attached at the exposed ends of the rebar to monitor the wave transmission along the rebar with and without simulated corrosion, which was introduced in the form of partial removal of material from the rebar. Experimental testing demonstrated that the presence of concrete had a significant influence on the propagation characteristics of guided waves along the rebar. In consideration of the inevitable discrepancies in different concrete beams due to individual specimen preparation and sensor installation, the time-reversal process was applied to identify the damage. A damage index was defined based on the correlation coefficient between the actuated and the reconstructed wave signals. Wavelet transform was applied to overcome the wave conversion difficulty and to reduce the noise in the captured wave signals. Damage of different sizes was introduced and then was correlated with the damage index. Enlarging the damage size resulted in an increase in the level of distortion in the reconstructed wave signals, and consequently, a higher damage index was obtained. The results demonstrate the efficiency of the time-reversal process in identifying damage in rebar-reinforced concrete structures.
Nateghi, F, Shon, HK & Khabbaz, H 2014, 'Development of a new poly silicate ferric coagulant and its application to coagulation- membrane filtration hybrid system in wastewater treatment', DESALINATION AND WATER TREATMENT, vol. 52, no. 4-6, pp. 663-669.
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Coagulation is one of the effective pretreatment stages in membrane filtration of wastewaters to produce clean water. Using a suitable coagulant, one can mitigate membrane fouling. Membrane fouling is a process where particles deposit onto a membrane surface or into membrane pores in a way that degrades the membrane's performance. Research in this area is currently being focused on development of improved coagulation reagents such as poly silicate ferric (PSiFe), which has a high molecular weight and large number of positive surface charges with high efficiency at low doses. In this paper, PSiFe was prepared by following two approaches: (a) acidification of water glass solution using HCl followed by FeCl3 addition (old-PSiFe); (b) acidification of water glass solution by passing it through an acidic ion exchange resin followed by fresh FeCl3 addition under different Fe/Si molar ratios (new-PSiFe). These coagulants were characterised by X-ray diffraction and scanning electron microscopy. According to coagulation jar test results when Fe/Si = 1, the best performance was achieved in terms of turbidity, total organic carbon (TOC) and UV254 removals. Another aspect is the comparison of the old-PSiFe, FeCl3 and new-PSiFe which showed that in a membrane filtration system, using the new-PSiFe not only reduces the required transmembrane pressure (TMP) due to lower fouling, but also improves the TOC removal efficiency. © 2013 © 2013 Balaban Desalination Publications. All rights reserved.
Nguyen, LD, Fatahi, B & Khabbaz, H 2014, 'A constitutive model for cemented clays capturing cementation degradation', INTERNATIONAL JOURNAL OF PLASTICITY, vol. 56, pp. 1-18.
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Laboratory experiments show that the effect of cementation on clays gradually diminishes as the confining pressure increases (particularly at high confining pressures) due to the degradation of cementation bonds. The main aim of this paper is to propose a constitutive model for cemented clays, referred to as the Cemented Cam Clay model (CCC), to simulate the cementation degradation during loading. The failure envelope of the proposed model is formulated to describe the behaviour of the cemented clay at a low pressure range similar to over-consolidated soils, while it merges with the Critical State Line of reconstituted sample gradually as the confining pressure continues to increase. In order to examine the stress-strain behaviour of cemented clays, an energy dissipation equation is developed inspired by the Modified Cam Clay model. The characteristics of the proposed model, including a non-associated plastic potential function and elasto-plastic stress-strain relationship, are presented in light of the Critical State concept. Validity of the proposed constitutive model derived from the modified energy equation is evaluated against triaxial test results for cemented clays available in literature. © 2014 Published by Elsevier Ltd. All rights reserved.
Noushini, A, Samali, B & Vessalas, K 2014, 'Static mechanical properties of polyvinyl alcohol fibre reinforced concrete (PVA-FRC)', MAGAZINE OF CONCRETE RESEARCH, vol. 66, no. 9, pp. 465-483.
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This investigation assessed the performance of polyvinyl alcohol (PVA) fibres of 6 mm and 12 mm length in concrete. Based on total concrete volume, four fibre fractions (0.125, 0.25, 0.375 and 0.5%) were evaluated for their effect on fresh and hardened properties of PVA fibre reinforced concretes (PVA-FRCs). Fly ash was also used as partial replacement of Portland cement in all the mixes. By carrying out a comprehensive set of experiments (compressive strength, splitting tensile strength, modulus of elasticity, modulus of rupture and residual flexural strength), it was observed that PVA fibre significantly enhances the static mechanical properties of concrete as well as improving its post-peak response and ductile behaviour.
Parsa-Pajouh, A, Fatahi, B, Vincent, P & Khabbaz, H 2014, 'Analyzing consolidation data to predict smear zone characteristics induced by vertical drain installation for soft soil improvement', GEOMECHANICS AND ENGINEERING, vol. 7, no. 1, pp. 105-131.
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In this paper, the effects of variability of smear zone characteristics induced by installation of prefabricated vertical drains on the preloading design are investigated employing analytical and numerical approaches. Conventional radial consolidation theory has been adopted to conduct analytical parametric studies considering variations of smear zone permeability and extent. FLAC 2D finite difference software has been employed to conduct the numerical simulations. The finite difference analyses have been verified using three case studies including two embankments and a large-scale laboratory consolidometer with a central geosynthetic vertical drain. A comprehensive numerical parametric study is conducted to investigate the influence of smear zone permeability and extent on the model predictions. Furthermore, the construction of the trial embankment is recommended as a reliable solution to estimate accurate smear zone properties and minimise the post construction settlement. A back-calculation procedure is employed to determine the minimum required waiting time after construction of the trial embankment to predict the smear zone characteristics precisely. Results of this study indicate that the accurate smear zone permeability and extent can be back-calculated when 30% degree of consolidation is obtained after construction of the trial embankment. © 2014 Techno-Press, Ltd.
Parsa-Pajouh, A, Fatahi, B, Vincent, P & Khabbaz, H 2014, 'Trial Embankment Analysis to Predict Smear Zone Characteristics Induced by Prefabricated Vertical Drain Installation', Geotechnical and Geological Engineering, vol. 32, no. 5, pp. 1187-1210.
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© 2014, Springer International Publishing Switzerland. In this study, FLAC finite difference software has been adopted to simulate the performance of the ground improved using prefabricated vertical drains assisted preloading, considering smear zone characteristics. The numerical code has been applied to predict smear zone properties employing a back calculation procedure using the results of several case studies. The construction of a trial embankment is proposed as a reliable method to predict the smear zone characteristics. The proposed back calculation method is applied to estimate the minimum required degree of consolidation and consequently the minimum required preloading time, resulting in a reliable estimation of the smear zone permeability and extent. Three preloading case studies considering both conventional preloading and vacuum assisted preloading have been simulated to verify the numerical code and to conduct the parametric study using the back calculation procedure. According to the results, the properties of the smear zone can be back-calculated reliably, when at least 33 % degree of consolidation due to trial embankment construction is achieved.
Quang, NK, Hieu, NT & Ha, QP 2014, 'FPGA-Based Sensorless PMSM Speed Control Using Reduced-Order Extended Kalman Filters', IEEE Transactions on Industrial Electronics, vol. 61, no. 12, pp. 6574-6582.
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© 2014 IEEE. This paper presents the design and implementation of a field-programmable gate array (FPGA)-based architecture for the speed control of sensorless permanent-magnet synchronous motor (PMSM) drives. For the reduction of computation resources, as well as accuracy improvement in the rotor position estimation, a parallel reduced-order extended Kalman filter (EKF) is proposed in this work. Compared with an EKF, the system order is reduced and the iteration process is greatly simplified, resulting in significant savings of resource utility, while maintaining high estimation performance. The whole control system includes a current-control-and-coordinate-transformation unit, a proportional-integral (PI) speed controller, and other accessory modules, all implemented in a single FPGA chip. A hardware description language is adopted to describe advantageous features of the proposed control system. Moreover, the finite-state-machine method is applied with the purpose to reduce logic elements used in the FPGA chip. The validity of the approach is verified through simulation based on the Modelsim/Simulink cosimulation method. Finally, experimental results are obtained on an FPGA platform with an inverter-fed PMSM to show the feasibility and effectiveness of the proposed system-on-programmable-chip for PMSM drives.
Remennikov, AM, Mutton, V, Nimbalkar, S & Ren, T 2014, 'Experimental and numerical investigation of high-yield grout ore pass plugs to resist impact loads', INTERNATIONAL JOURNAL OF ROCK MECHANICS AND MINING SCIENCES, vol. 70, pp. 1-15.
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In the last fifteen years, Tekseal high yield foaming grout ore pass plugs that could later be easily removed, have been poured above chute maintenance areas providing protection from high energy rock impact and isolating workers from the hazard. Construction and removal methods will be briefly explained. Since it is not economically feasible to investigate the problem of ore pass plug impact response using full-scale experimental studies, this paper presents a combined four-stage approach that includes (1) laboratory testing to investigate the mechanical behaviour of the high-yield foaming grout; (2) high-precision impact testing of reduced-scale models of ore pass plugs; (3) high-fidelity physics-based numerical model calibration using experimental data; and (4) full-scale modelling of mine ore pass plugs using calibrated material models. To calibrate numerical models, three one-metre diameter steel pipes filled with Tekseal high yield foaming grout were tested with falling steel projectiles of different shapes. Impact tests provided data on the depth of penetration and size of the craters formed by the projectiles. Numerical models were calibrated by optimising the material parameters and modelling techniques to provide the best match with the experimental results. Full-scale numerical models of ore pass plugs were developed for typical ore pass dimensions and subjected to impact events by falling rock projectiles. The proposed approach has allowed investigating energy absorbing characteristics of ore pass plugs to further predict and increase understanding of their capacity to withstand high-speed impacts by large falling projectiles. © 2014 Elsevier Ltd.
Šimon, P, Thomas, P, Dubaj, T, Cibulková, Z, Peller, A & Veverka, M 2014, 'The mathematical incorrectness of the integral isoconversional methods in case of variable activation energy and the consequences', Journal of Thermal Analysis and Calorimetry, vol. 115, no. 1, pp. 853-859.
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Kinetic parameters resulting from the application of isoconversional methods mostly depend on the degree of conversion. This paper shows that the integral isoconversional methods are mathematically incorrect if the activation energy depends on conversion. In this case, the incorrectness resides in improper separation of variables in the general rate equation. As a consequence, non-sensical snake-like shape of the conversion versus time curves is observed when the kinetic results are extrapolated to lower temperatures. © 2013 Akadémiai Kiadó, Budapest, Hungary.
Sofi, M, Mendis, P, Baweja, D & Mak, S 2014, 'Influence of ambient temperature on early age concrete behaviour of anchorage zones', CONSTRUCTION AND BUILDING MATERIALS, vol. 53, pp. 1-12.
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SUN, QD, INDRARATNA, B & NIMBALKAR, S 2014, 'Effect of cyclic loading frequency on the permanent deformation and degradation of railway ballast', Géotechnique, vol. 64, no. 9, pp. 746-751.
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A series of large-scale cyclic triaxial tests were conducted on latite basalt aggregates (ballast) to investigate how the frequency f affects the permanent deformation and degradation of railway ballast. During testing the frequency was varied from 5 Hz to 60 Hz to simulate a range of train speeds from about 40 km/h to 400 km/h. Three categories of permanent deformation mechanisms were observed in response to the applied cyclic loads, namely, the inception of plastic shakedown (f ≤ 20 Hz), then plastic shakedown and ratcheting (30 Hz ≤ f ≤ 50 Hz), followed by plastic collapse at higher frequencies (f ≥ 60 Hz). The permanent strain of ballast and particle breakage increased with the frequency and number of load cycles. A cyclic strain ratio was introduced to capture the effect of frequency on the permanent axial and volumetric strains, respectively. An empirical equation was formulated to represent this relationship for latite basalt, and a critical train speed was identified. A good correlation was obtained between particle breakage and volumetric strain under cyclic loading.
Sun, Y, Indraratna, B & Nimbalkar, S 2014, 'Three-dimensional characterisation of particle size and shape for ballast', Géotechnique Letters, vol. 4, no. 3, pp. 197-202.
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The size and shape of particles influence how effectively coarse angular aggregates of ballast interact. The aim of this study was to improve the characterisation of ballast particles using a three-dimensional (3D) imaging method. Various size and shape indices, such as elongation ratio, sphericity and roundness, were determined from the scanned 3D images. A modified index called ‘ellipsoidness’ was proposed to capture adequately the shape of the 3D particles. Variation of these indices with particle size was studied. Comparison of the 3D true sphericity and the corresponding two-dimensional sphericity indicated that the latter would underestimate sphericity. A modified approach for transforming particle size distribution to constriction size distribution is proposed by capturing the size and shape effects of particles.
Tabatabaiefar, HR & Fatahi, B 2014, 'Idealisation of soil-structure system to determine inelastic seismic response of mid-rise building frames', SOIL DYNAMICS AND EARTHQUAKE ENGINEERING, vol. 66, no. 1, pp. 339-351.
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In this study, a novel and enhanced soilstructure model is developed adopting the direct analysis method using FLAC 2D software to simulate the complex dynamic soil-structure interaction and treat the behaviour of both soil and structure with equal rigour simultaneously. To have a better judgment on the inelastic structural response, three types of mid-rise moment resisting building frames, including 5, 10, and 15 storey buildings are selected in conjunction with three soil types with the shear wave velocities less than 600 m/s, representing soil classes Ce, De and Ee, according to Australian Standards. The above mentioned frames have been analysed under two different boundary conditions: (i) fixed-base (no soil-structure interaction) and (ii) flexible-base (considering soil-structure interaction). The results of the analyses in terms of structural displacements and drifts for the above mentioned boundary conditions have been compared and discussed. It is concluded that considering dynamic soil-structure interaction effects in seismic design of moment resisting building frames resting on soil classes De and Ee is essential.
Tabatabaiefar, SHR, Fatahi, B & Samali, B 2014, 'An empirical relationship to determine lateral seismic response of mid-rise building frames under influence of soil-structure interaction', STRUCTURAL DESIGN OF TALL AND SPECIAL BUILDINGS, vol. 23, no. 7, pp. 526-548.
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n this study, to determine the elastic and inelastic structural responses of mid-rise building frames under the influence of soilstructure interaction, three types of mid-rise moment-resisting building frames, including 5-storey, 10-storey and 15-storey buildings are selected. In addition, three soil types with the shear wave velocities less than 600m/s, representing soil classes Ce, De and Ee according to AS 1170.42007 (Earthquake action in Australia, Australian Standards), having three bedrock depths of 10m, 20m and 30m are adopted. The structural sections are designed after conducting nonlinear time history analysis, on the basis of both elastic method and inelastic procedure considering elastic-perfectly plastic behaviour ofstructural elements. The frame sections are modelled and analysed, employing finite difference method adopting FLAC2D software under two different boundary conditions: (a) fixed base (no soilstructure interaction) and (b) considering soilstructure interaction. Fully nonlinear dynamic analyses under the influence of different earthquake records are conducted, and the results in terms of the maximum lateral displacements and base shears for the above mentioned boundary conditions for both elastic and inelastic behaviours of the structural models are obtained, compared and discussed. With the results, a comprehensive empirical relationship is proposed to determine the lateral displacements of the mid-rise moment-resisting building frames under earthquake and the influence of soilstructure interaction.
Tabatabaiefar, SHR, Fatahi, B & Samali, B 2014, 'Numerical and Experimental Investigations on Seismic Response of Building Frames under Influence of Soil-Structure Interaction', ADVANCES IN STRUCTURAL ENGINEERING, vol. 17, no. 1, pp. 109-130.
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In this study, an enhanced numerical soil-structure model has been developed which treats the behaviour of soil and structure with equal rigour. The proposed numerical soil-structure model has been verified and validated by performing experimental shaking table tests. To achieve this goal, a series of experimental shaking table tests were performed on the physical fixed based (structure directly fixed on top of the shaking table) and flexible base (considering soil and structure) models under the influence of four scaled earthquake acceleration records and the results were measured. Comparing the experimental results with the numerical analysis predictions, it is noted that the numerical predictions and laboratory measurements are in a good agreement. Thus, the proposed numerical soil-structure model is a valid and qualified method of simulation with sufficient accuracy which can be employed for further numerical soil-structure interaction investigation studies. Based on the predicted and observed values of lateral deflections of fixed base and flexible base models, lateral deflections of the flexible base model have noticeably amplified in comparison to the fixed base model. As a result of the lateral deflection amplifications, it is observed that the performance level of the scaled structural model changed significantly which could be safety threatening.
Tran, T & Ha, QP 2014, 'Decentralized Model Predictive Control for Networks of Linear Systems with Coupling Delay', JOURNAL OF OPTIMIZATION THEORY AND APPLICATIONS, vol. 161, no. 3, pp. 933-950.
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This paper presents a new dissipativity-based decentralized model predictive control strategy for networks of linear systems suffering from a bounded coupling delay. The notion of delay-robust dissipativity is introduced and applied to the development of interconnection stability conditions. The dissipation inequality of system trajectories is converted into a prognostic stability constraint for the optimization problem of model predictive control to guarantee the system stability. A recursive feasibility condition is derived for the constrained optimization problem, which is formulated in a semi-definite program. A numerical example of an interconnected three-unit process system is provided for illustrations. © 2013 Springer Science+Business Media New York.
Valipour, H, Khorsandnia, N, Crews, K & Foster, S 2014, 'A simple strategy for constitutive modelling of timber', CONSTRUCTION AND BUILDING MATERIALS, vol. 53, pp. 138-148.
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Velis, CA, Franco-Salinas, C, O’Sullivan, C, Najorka, J, Boccaccini, AR & Cheeseman, CR 2014, 'Up-Cycling Waste Glass to Minimal Water Adsorption/Absorption Lightweight Aggregate by Rapid Low Temperature Sintering: Optimization by Dual Process-Mixture Response Surface Methodology', Environmental Science & Technology, vol. 48, no. 13, pp. 7527-7535.
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Concerns with conservation of nonrenewable resources are propelling academic research regarding the use of recycled aggregates in concrete production. Concreteâs shrinkage is a phenomenon intimately linked to concrete loss of water, which is almost inevitable, since the majority of concrete structures is exposed to an environment where atmospheric humidity is below saturation condition. This paper presents an experimental study where concretes were produced varying water/cement ratio (from 0.4 to 0.8) and type and proportion of construction & demolition waste (concrete, cement, and red ceramic) used as coarse and fine recycled aggregates. Mathematical models correlating such variables with concreteâs shrinkage at 56 and 224 days of age were built. The results indicate that, for the age of 56 days, the data presented excessive variability, revealing only 4 of the 7 tested variables as significant. For the age of 224 days, the proposed model still presented considerable variability, however all tested variables were detected as significant. Results point out that substitution of natural aggregates by recycled aggregates increases shrinkage, being this effect stronger when substitution comprises fine aggregates. The most pronounced effect was associated to the use of recycled concrete fine aggregate. The slightest effect was observed using recycled concrete coarse aggregate.
Wu, C, Chanda, E & Willison, J 2014, 'Implementation and outcomes of online self and peer assessment on group based honours research projects', Assessment & Evaluation in Higher Education, vol. 39, no. 1, pp. 21-37.
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Xia, Y, Wu, C, Zhang, F, Li, Z-X & Bennett, T 2014, 'Numerical Analysis of Foam-Protected RC Members under Blast Loads', International Journal of Protective Structures, vol. 5, no. 4, pp. 367-390.
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Due to the threat of terrorist activities worldwide, research on the protection of building structures from the effects of explosions is critical in order to avoid catastrophic damage to buildings. Protecting our infrastructures means protecting lives. Metallic foam is an economical, light-weight and recyclable material used as a sacrificial cladding to protect structures. Its efficient energy absorption enables metallic foam to mitigate the blast energy acting on the protected structure. This paper describes our numerical investigation of the protective performance of metallic foam cladding on reinforced concrete (RC) structural members using LS-DYNA. In the numerical model, Modified Honeycomb (Material 126) from the LS-DYNA material library was used to represent the aluminium foam while Continuous Surface Cap Model (Material 159) was selected to model the behaviour of concrete. The numerical model was validated by field blast testing results. Using the validated numerical model, parametric studies were conducted to assess the influence of different foam properties on the pressure-impulse (P-I) diagrams of the foam-protected RC slabs. The influence of the thickness of the RC members was also investigated. The derived P-I diagrams will prove useful in the preliminary design of the foam cladding on RC members.
Xiao, R, Li, J & Shrestha, R 2014, 'Investigations of Vibration Based Condition Assessment of Timber Beams Strengthened with Fiber Reinforced Polymer', ADVANCES IN CIVIL ENGINEERING AND BUILDING MATERIALS III, vol. 831, pp. 53-57.
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In recent years, research trend on structural condition assessments have largely shifted toward utilizing vibration based methods for structural damage detection and evaluation. On the other hand, research and applications on use of fiber reinforce polymer (FRP) on timber for strengthening or repair damaged timber members in various types of timber structures has also become increasingly popular. Although the application of FRP for repair and/or strengthening of structures has been researched for a long time, research on non-destructive assessment or evaluation of the effectiveness and reliability after FRP repairing or strengthening is yet to be carried out. In this paper, the authors made an attempt on investigation of such issue utilizing Damage Index method, which is a robust vibration-based approach for damage detection. The investigation was aiming at localizing and quantifying damage in timber beams and, more importantly evaluating the effectiveness after the damage was repaired. An experimental program was carried out on five laminated veneer lumber (LVL) beams. Various damage scenarios (i.e. severe, medium, light damage) are introduced on these beams and then repaired with carbon fiber reinforced polymer (CFRP). Experimental results indicate that the use of CFRP was effective in repairing the damaged timber beams. Utilizing Damage Index method can accurately detect the damage location. However, the investigation also shows that direct application of the Damage Index for evaluation of the effectiveness of rehabilitation of the damaged timber beam is not satisfactory. Further investigation and modification of the Damage Index method will be carried out in next stage research.
Xu, J, Wu, C & Li, Z-X 2014, 'Analysis of direct shear failure mode for RC slabs under external explosive loading', International Journal of Impact Engineering, vol. 69, pp. 136-148.
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The single degree of freedom system (SDOF) is used to predict the shear responses of RC (reinforced concrete) members under external blast loading in the present study. An RC member suffering a blast may experience both flexural and shear failure modes. Under very high amplitude short duration shock, structural failure is usually governed by direct shear loading, whereas under low amplitude long duration shock, the structural failure is most likely governed by flexural damage. However, most previous studies are based on the assumption that flexural response dominates the failure mode without taking shear failure into consideration. In the present study, dynamic response equations of a structural member experiencing direct shear failure are derived for elastic, plastic and elasto-plastic shear resistance-slip models. With these equations the P-I curves of both flexural and direct shear failure modes are generated for an RC slab. Furthermore, a parametric study is conducted to investigate the effect of different parameters of RC slabs on the pressure-impulse (P-I) diagrams based on the elasto-plastic model. Finally, based on the results from the parametric studies, curve fitting technique is used to generate the P-I curves for RC slabs in a simplified way. © 2014 Elsevier Ltd. All rights reserved.
Alamdari, MM, Li, J & Samali, B 1970, 'Damage Localisation Using Symbolic Time Series Approach', Conference Proceedings of the Society for Experimental Mechanics Series, Conference of Society for Experimental Mechanics Series, Springer International Publishing, pp. 109-115.
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© The Society for Experimental Mechanics, Inc. 2014. The objective of this paper is to localise damage in a single or multiple state at early stages of development based on the principles of symbolic dynamics. Symbolic Time Series Analysis (STSA) of noise-contaminated responses is used for feature extraction to detect and localise a gradually evolving deterioration in the structure according to the changes in the statistical behaviour of symbol sequences. The method consists of four primary steps: (1) generating the time series data by a set of measurements over time at evenly spaced locations along the structure; (2) creating the symbol space to generate symbol sequences based on the wavelet transformed version of time series data; (3) developing the symbol probability vectors to achieve anomaly measures; (4) localising damage based on any sudden variation in anomaly measure of two adjacent locations. The method was applied to a clamped–clamped beam subjected to random excitation in presence of 5 % white noise to examine the efficiency and limitations of the method. Simulation results under various damage conditions confirmed the efficiency of the proposed approach for localisation of gradually evolving deterioration in the structure, however, for the future work the method needs to be verified by experimental data.
Aoki, Y, Valipour, H, Samali, B & Saleh, A 1970, 'Sensitivity Analysis For Steel Deck Of A Cable-Stayed Bridge Subjected To Blast Loadings', Proceedings of the 23rd Australasian Conference on the Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, Southern Cross university, Byron Bay, Australia, pp. 1039-1044.
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In design of cable-stayed bridges, sudden loss of cables are usually associated with material as well asgeometrical nonlinearities which may trigger progressive collapse of the entire bridge. Accordingly,the possible reasons of loss of cable would be the blast loadings, which is one of the concernedsituations after 911 terrorist attacks. In this paper, detailed 3D finite element models of a hypotheticalcable-stayed bridge deck is developed and analysed with material and geometrical nonlinearitiesincluded. A parametric study is undertaken to investigate the effect of blast loadings with differentmaterial properties, section properties and different amount of explosive materials, to determinedamaged area, number of loss of shell elements as well as cable elements due to explosion. Withregard to the results of FE analysis, it is concluded that the maximum 3 cables would be lost by thelarge amount of TNT equivalent material due to damage of the anchorage zone.
Azari, B, Fatahi, B, Khabbaz, H & Vincent, P 1970, 'Elastic Visco-Plastic Behaviour of Soft Soils Improved with Preloading and Vertical Drains', Pavement Performance Monitoring, Modeling, and Management, Geo-Hubei 2014 International Conference on Sustainable Civil Infrastructure, American Society of Civil Engineers, China, pp. 17-24.
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In this study, a numerical solution adopting an elastic visco-plastic model with nonlinear creep function incorporated in the consolidation equations has been developed to investigate the time-dependent behavior of soft soil deposits improved with vertical drains and preloading. The employed elastic visco-plastic model is based on the framework of the modified Cam-Clay model capturing soil creep during excess pore water pressure dissipation. In addition, nonlinear variations of creep strain rate with stress and time and permeability variations during the consolidation process are considered. The developed numerical model is validated against Ska-Edeby test fill with the available long-term settlement and excess pore water pressure monitoring results for the soft clay deposit improved with vertical drains assisted preloading. Practicing engineers can adopt the developed code and guidelines to predict the long-term performance of embankments on soft soil improved using preloading. © ASCE 2014.
Baweja, D, Benn, BT & Mills, JE 1970, 'The compressive strength of mortar made with cement containing limestone mineral addition, cement kiln dust and fly', Proceedings of the 23rd Australiasian Conference on the Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, Southern Cross University, Byron Bay, Australia, pp. 119-124.
Benn, BT, Baweja, D & Mills, JE 1970, 'The influence of increased levels of limestone mineral addition used in combination with cement kiln dust on chloride ion penetration', RILEM International workshop on performance-based specification and control of concrete durability, RILEM International Workshop on Performance Based Specification and Control of Concrete Durability, RILEM, University of Zagreb, pp. 167-174.
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In 2010 the Australian cement standard, AS 3972 - General purpose and blended cement, increased the maximum mineral addition level to 7.5% from 5% and in addition allowed up to 5% of the mineral addition to be inorganic mineral materials derived from the clinker production process e.g. cement kiln dust. This paper will present the preliminary results of a research program that is investigating chloride ion ingress of mortar and concrete made with cement containing increased levels of mineral addition, where the mineral addition is a combination of limestone and cement kiln dust. The early results based on the Bulk Diffusion Test (ASTM C 1556/NT Build 443) and the Rapid Migration Test (AASHTO TP 64/NT Build 492) tests indicate that with a 10% mineral addition, based on limestone and 5% CKD, there does appear to be an increase in the rate of chloride penetration into mortar but the investigation will not be completed for at least another two years
Brennan, J, Ding, G, Wonschik, C-R & Vessalas, K 1970, 'A Closed-Loop System of Construction and Demolition Waste Recycling', Proceedings of the International Symposium on Automation and Robotics in Construction (IAARC), 31st International Symposium on Automation and Robotics in Construction, International Association for Automation and Robotics in Construction (IAARC), Sydney, Australia, pp. 499-505.
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This study discusses the construction and demolition waste recycling stream both in Australia and in Germany. Differences and commonalities in commercial practices between the two countries are outlined, and open research questions are introduced. Following McDonough and Braungart’s cradle-to-cradle theorem, and ideal closed-loop system within the building life cycle is proposed. Deficiencies and efficiencies in the closed-loop system are reported and assessed and related parameters promoting or hindering the closed-loop system are evaluated. Results of the study demonstrate that reusable and non-reusable materials generated from construction and demolition operations, which are destined for landfill, are categorized differently between the recycling systems used in Australia and Germany.
Carper, KL 1970, '10th International Conference on Shock & Impact Loads on Structures', Journal of Performance of Constructed Facilities, International Conference on Shock and Impact Loads on Structures, American Society of Civil Engineers (ASCE), Singapore, pp. 205-205.
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Concrete-filled double skin steel tubes (CFDST) have widely been used in constructing high-rise buildings, arch bridges and factories. Much research has been done to study its behaviour under axial compression. However, limited information can be found on its performance under lateral impact loading, especially under blast loading. In this paper, numerical models are developed for CFDST with two different cross sections: one is with CHS (circular hollow section) outer and CHS (circular hollow section) inner, and the other one is with SHS (square hollow section) outer and SHS (square hollow section) inner. Conventional concrete is filled in double skin steel tubes. Different blast loadings are applied on the surface of these columns for dynamic analysis. In addition, different axial loads are also applied on the columns to simulate the combined load condition. The displacement-time history obtained from each simulation is recorded and then compared. The key factors that determine the performance of CFDST columns under blast loading are discussed.
Dackermann, U, Smith, WA, Li, J & Randall, RB 1970, 'On the use of the cepstrum and artificial neural networks to identify structural mass changes from response-only measurements', PROCEEDINGS OF INTERNATIONAL CONFERENCE ON NOISE AND VIBRATION ENGINEERING (ISMA2014) AND INTERNATIONAL CONFERENCE ON UNCERTAINTY IN STRUCTURAL DYNAMICS (USD2014), International Conference on Noise and Vibration Engineering, KU Leuven - Departement Werktuigkunde, Leuven, Belgium, pp. 3739-3750.
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This paper presents a damage identification technique based on response-only data utilising cepstrum analysis and artificial neural networks (ANNs) for the identification of added mass in a two-storey framed structure. The proposed technique applies cepstrum-based operational modal analysis (OMA) for the regeneration of frequency response functions (FRFs), and added mass is detected through the combined use of principal component analysis (PCA) for data compression and ANNs for feature extraction and pattern recognition. In particular, different treatments of the zeros in the curve-fitting of the transfer function cepstrum are investigated to improve the automation potential of the method for application in continuous online structural health monitoring (SHM). The proposed technique is validated on a laboratory structure tested on a large-scale shake table with ambient base loading. The results of the investigation show that the method is effective in identifying added mass based on response-only measurements.
Erkmen, RE, Bradford, MA & Crews, K 1970, 'Treatment of locking behaviour for displacement-based finite element analysis of composite beams', STRUCTURAL ENGINEERING AND MECHANICS, Advances in Structural Engineering and Mechanics, Technopress, Soul, Korea, pp. 163-180.
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Firouzianhaji, A, Saleh, A & Samali, B 1970, 'Non-Linear Finite Element Analysis Of Base-Plate Connections Used In Industrial Pallet Rack Structures', Proceedings of Australasian Structural Engineering Conference 2014, Australasian Structural Engineering Conference, ASEC, Auckland, NZ, pp. 1-9.
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This paper presents the results of experimental and FE simulations of a typical base plate connection used for industrial storage racks with two different floor anchoring configurations. The experimental results presented provide moment rotation curves of the base plates for 5 different axial loads imposed on the upright. The experimental setup models the same structural conditions stipulated in EN 15512 but with an alternative test rig setup that overcomes some drawbacks of the test arrangement proposed in EN 15512. Using FE models that incorporate material, geometric and contact non-linearity, the base plates were analysed for both monotonic and cyclic loading.
Firouzianhaji, A, Saleh, A & Samali, B 1970, 'Stability Analysis of Steel Storage Rack Structures', Proceedings of the 23rd Australasian Conference on the Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, Southern Cross University, Byron Bay, Australia, pp. 583-588.
Gandhi, S, Sankaran, S, Er, M, Orr, K & Khabbaz, H 1970, 'Developing Technology-Assisted Multi-Disciplinary Learning Strategies', Proceedings of the International Symposium on Automation and Robotics in Construction (IAARC), 31st International Symposium on Automation and Robotics in Construction, International Association for Automation and Robotics in Construction (IAARC), Sydney, pp. 346-353.
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The construction industry is multi-disciplinary and collaborative in nature. Project managers are expected to understand the relations, roles and responsibilities in this collaborative working environment. Construction project managers need to be equipped with skills to process and understand the principles of interdisciplinary working. In order to keep pace with industry requirements, it is necessary for universities to teach subjects in tertiary education courses that educate and motivate construction students towards interdisciplinary working. This paper is based on a research project aimed at understanding opportunities and challenges for introducing subjects that require students from different disciplines to work together on an integrated project. In order to teach interdisciplinary working principles to project management students, a new post-graduate subject, Integrated Project Delivery, was introduced in the Master of Project Management at the University of Technology Sydney (UTS) as part of a construction sub-major. The subject was designed and teaching materials prepared based on inputs from architecture, engineering and construction management academics. In the teaching of the subject, interdisciplinary student teams were formed based on educational background and professional experience. An (pedagogical) action research approach was adopted to study the challenges and benefits of new ways of learning in line with the UTS learning strategies being adopted by academics. The main finding of this research concluded that project-based learning is very valuable to both students and industry alike as it promotes working on a live project enthusiastically and gaining industry experience in new ways of working adopted by industry. Working in multi-disciplinary teams requires students to respect the other team participants from different backgrounds, inculcating values of team spirit and discouraging adversarial behaviours. Furthermore this research ...
Gu, X, Li, J & Li, Y 1970, 'Innovative semi-active storey isolation system utilising novel magnetorheological elastomer base isolators', Proceedings of the 23rd Australasian Conference on the Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, Southern Cross University, Byron Bay, Australia, pp. 925-930.
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Seismic base isolation has been a widely adopted technique for earthquake protection of civil infrastructures. As the technology matures, new innovative designs of the base isolation systems become increasingly attractive to researchers, especially storey base isolation systems due to its design flexibility and better performance for seismic protection. Moreover, considering the unpredictable and diverse nature of earthquakes, the conventional base isolation systems have reached their limit due to their inherent passive nature which is incapable to adjust their isolation frequencies according to the characteristics of the earthquakes. A recent advance on the development of an adaptive magneto-rheological elastomer (MRE) base isolator provides an opportunity for the research and development on new adaptive base isolation systems. In this paper, an innovative semi-active storey isolation system utilising the novel magneto-rheological elastomer base isolator has been proposed. The proposed isolation system design incorporates adaptive magneto-rheological elastomer isolators under each storey of the structure instead of being only installed beneath of the entire structure. Such innovative system allows high authority semiactive control of storey responses by instantly changing stiffness of the isolator. Extensive simulation has been conducted to investigate such system using 5-storey international benchmark model under four benchmark earthquakes.
Hailu, M, Shrestha, R & Crews, K 1970, 'Long-term experimental investigation of timber composite beams in cyclic humidity conditions', WCTE 2014 - World Conference on Timber Engineering, Proceedings, World Conference on Timber Engineering (WCTE), Quebec City, Canada.
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A long term laboratory investigation on two six-meter-span timber composite beams was started from March 2012 at the University of Technology Sydney. These timber composites were made of laminated veneer lumber (LVL). The web and the flanges of the composite timber section were connected using screw-gluing technique. The specimens have been under sustained loads of (2.1kPa) and the environmental conditions was cyclically alternated between normal and very humid conditions whilst the temperature remained quasi constant (22 °C)-typical cycle duration was six to eight weeks. With regard to EC 5, the environmental conditions can be classified as service class 3 where the relative humidity of the air exceeds 85% and the moisture content of the timber samples reaches 20%. During the test, the mid-span deflection, moisture content of the timber beams and relative humidity of the air were continuously monitored. The paper presents the results and observations of the long-term test to-date and the test is continuing.
Hailu, M, Shrestha, R & Crews, K 1970, 'Long-term experimental investigation of timber composite beams in cyclic humidity conditions', WCTE 2014 - World Conference on Timber Engineering, Proceedings.
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A long term laboratory investigation on two six-meter-span timber composite beams was started from March 2012 at the University of Technology Sydney. These timber composites were made of laminated veneer lumber (LVL). The web and the flanges of the composite timber section were connected using screw-gluing technique. The specimens have been under sustained loads of (2.1kPa) and the environmental conditions was cyclically alternated between normal and very humid conditions whilst the temperature remained quasi constant (22 °C)-typical cycle duration was six to eight weeks. With regard to EC 5, the environmental conditions can be classified as service class 3 where the relative humidity of the air exceeds 85% and the moisture content of the timber samples reaches 20%. During the test, the mid-span deflection, moisture content of the timber beams and relative humidity of the air were continuously monitored. The paper presents the results and observations of the long-term test to-date and the test is continuing.
Hailu, M, Shrestha, R & Crews, KI 1970, 'Timber composite floor beams under 2 years lon-term load', Proceedings of the 23rd Australasian Conference on the Mechanics of Structures and Materials (ACMSM23), Australasian Conference on the Mechanics of Structures and Materials, Southern Cross University, Byron Bay, Australia, pp. 607-612.
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The long-term behaviour of composite beams is characterised by the response of its component parts (flanges and webs) to load, moisture content, temperature and relative humidity of the environment. This paper reports the results of a two years long-term test on two 6 m span composite floor beams made of laminated veneer lumber (LVL) under service load performed in an indoor, semi-controlled, and unheated environment. The environmental conditions were characterized by artificially induced cyclic air humidity with quasi-constant temperature. These conditions can be characterized as reasonably severe and presumably close to service class 3 according to Eurocode 5. During the test, the mid-span deflection, moisture content and air humidity were monitored. The paper recommends a creep factor for design of timber composite beams in severe environmental conditions.
Hassani Esgandani, M, Vessalas, K, Baweja, D & Schmidt, Z 1970, 'Effect Of Chemical Admixtures On Water Penetration Of Concrete', Proceedings of RILEM International workshop on performance-based specification and control of concrete durability, RILEM International workshop on performance-based specification and control of concrete durability, RILEM, Zagreb, Croatia, pp. 209-216.
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Durability of concrete is in part determined by its resistance to the penetration of deleterious substances entering as a liquid or gas that is considered to be a function of its permeation capacity. Permeation capacity is controlled by the connectivity of pores that exist in the cementitious matrix and paste-aggregate boundaries. The presence of chemical admixtures in a mixture can greatly reduce the permeation capacity of hardened concrete by several orders of magnitude. Permeability-reducing admixtures are effective in blocking capillary pores by making them hydrophobic as well as depositing pore-blocking products into the pores.This paper presents an experimental study into the effectiveness of using permeabilityreducing admixtures including hydrophobic pore blockers and crystalline self-sealers. Concretes with increasing w/c ratios of 0.4, 0.5 and 0.6 have been investigated. The effect of admixtures on water penetration has been assessed through monitoring the changes in mass transport mechanisms. In addition to the available standard test methods, the coefficient of permeability of water has been directly determined using a specially developed test method described in this paper. Results indicate that permeability-reducing admixtures can reduce the water penetration of concrete significantly if used correctly and if the design intent is defined.
Ho, L, Fatahi, B & Khabbaz, H 1970, 'Analytical solution for one-dimensional consolidation of unsaturated soil deposit subjected to step loading', UNSATURATED SOILS: RESEARCH & APPLICATIONS, VOLS 1 AND 2, International conference on Unsaturated Soils, Taylor & Francis Group, Sydney, pp. 1763-1769.
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This paper discusses a simple yet precise analytical solution for one-dimensional (1-D) consolidation of an unsaturated soil deposit subjected to a step loading. This solution is derived from nonlinear governing equations of flow using eigenfunction expansions and Laplace transform techniques. In addition, the mathematical development adopts one-way drainage condition for the unsaturated soil, in which the top boundary is permeable to the air and water phases whereas the base is impervious to these phases. Eigenfunctions and eigenvalues are parts of the general solution and can be obtained based on the proposed drainage boundary condition. Furthermore, uniformly distributed initial pore pressures can be used to determine the initial generalised Fourier coefficients. The Laplace transform method is adopted to solve the first-order differential equations. Once the equations with transformed domain are obtained, the final solutions, which are proposed to be functions of time (t) and depth (z), can be achieved by taking an inverse Laplace transform. A worked example is provided to present the consolidation characteristics of unsaturated soils based on the proposed solution. Significance of air to water permeability ratio on the excess pore-water and pore-air pressure dissipation and compression is investigated and discussed. © 2014 Taylor & Francis Group.
Ho, L, Fatahi, B & Khabbaz, H 1970, 'One-Dimensional Consolidation of Unsaturated Soil Deposit with Various Initial Conditions', Soil Behavior and Geomechanics, Geo-Shanghai 2014, American Society of Civil Engineers, Shanghai, pp. 145-155.
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This study presents a novel analytical solution for one-dimensional (1-D) consolidation for unsaturated soils using the Eigen function expansion method to solve inhomogeneous governing equations of air and water phases. Eigen functions and eigen values are parts of the general solution and can be obtained based on the proposed boundary condition. Additionally, the Laplace transform method is adopted to solve the first-order differential equations. Once all equations with transformed domain are obtained, the final solutions, which are proposed to be functions of time and depth, can be achieved by taking an inverse Laplace transform. The mathematical procedure accentuates a non-uniform initial condition in which initial excess pore pressures are linearly decreasing with depth. Dimensionless parameters a and w that control the gradients of distributions of initial excess pore-air and pore-water pressures, respectively, are introduced in this paper. A worked example is provided to investigate effects of a and w on the consolidation behaviour of unsaturated soils. © 2014 American Society of Civil Engineers.
Hunt, A, Stuart, B, Thomas, P, James, D, David, B, Geneste, J-M & Delannoy, J-J 1970, 'Characterisation of ochre pigments from Jawoyn rock art paintings of Arnhem Land, Australia', International Symposium on Archaeometry, Los Angeles.
Indraratna, B, Nimbalkar, S & Rujikiatkamjorn, C 1970, 'Preface', Transportation Geotechnics, Elsevier BV, pp. 145-146.
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Indraratna, B, Nimbalkar, S, Rujikiatkamjorn, C & Heitor, A 1970, 'Ground improvement in transport geotechnics – from theory to practice', Computer Methods and Recent Advances in Geomechanics - Proceedings of the 14th Int. Conference of International Association for Computer Methods and Recent Advances in Geomechanics, IACMAG 2014, International Conference of the International Association for Computer Methods and Advances in Geomechanics, CRC Press, Kyoto, Japan, pp. 35-44.
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In order to meet the ever-increasing demand for public and freight mobility, concerted efforts are needed to improve transport efficiency, and ensure the maintenance cost of highways and railways to sustainable levels. Ballast and subgrade are major components of rail track infrastructure, and understanding their integrated behaviour as layered strata is of utmost importance. In order to investigate their performance, sophisticated numerical modeling techniques using the Discrete Element Method (DEM) and Finite Element Method (FEM) are commonly employed, but the micro-mechanics of particulate interactions are often taken for granted rather than studied in depth. The salient aspects of particle degradation and confining pressure are discussed through the use of advanced elasto-plastic constitutive models. Applications of DEM to study the behavior of coal-fouled ballast subjected to cyclic loading using a track process simulation apparatus are also presented. The DEM enabled the discrete nature of ballast aggregates to be modeled considering their realistic size and shape, as well as through the force chains developed at contacts.A radial consolidation model under cyclic loading is proposed to capture the behavior of soft clays subjected to cyclic loadingwhen radial drainage is allowed during the loading period. The effects of the cyclic stress history on the generation of excess pore pressure are considered in the proposed model. This model is verified against the results of large-scale triaxial tests. In addition, the study of the behavior of artificially compacted subgrade, is vital to avoid unwanted volume changes caused by moisture variation that can contribute to poor track performance. A model is proposed for assessing the performance of compacted subgrades by evaluating the small strain behavior, considering the soil matric suction, the water content and the compaction energy level. This paper discusses the stability of the transport infrastructure at small...
Indraratna, B, Rujikiatkamjorn, C & Nimbalkar, S 1970, 'Ground Improvement for Rail, Port and Road Infrastructure--From Theory to Practice', Ground Improvement and Geosynthetics, Geo-Shanghai 2014, American Society of Civil Engineers, pp. 1-19.
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The transportation infrastructure in coastal regions of Australia has been expanded in recent years due to high population density and increased traffic volume. Such expansions require the application of ground improvement techniques to improve performance and sustainability of the infrastructure. In this paper, innovative ground improvement techniques applicable to railway embankments, port reclamation and embankment fills are discussed. For ballasted rail tracks, the performance of different types of geosynthetics for improving the stability and drainage of railway tracks under high cyclic loading is investigated. Instrumented tracks were conducted to measure the in-situ stresses and deformations of ballast at Bulli, New South Wales (NSW), Australia. Furthermore, stabilization of soft formation soils underneath rail tracks using prefabricated vertical drains (PVDs) is also studied through finite element analyses and field measurements at Sandgate. The innovative use of the mixtures of coal wash (CW) and steel furnace slag (SFS) as the reclamation fill is demonstrated through laboratory and field investigations at the Outer Harbor extension of Port Kembla in Wollongong, NSW. The optimum CW-SFS mixtures that may meet most of the geotechnical specifications are proposed to be used as an effective structural fill. Finally, the design of the combined vacuum and surcharge fill system and the construction of the road embankment are described using a case study from the Pacific Highway upgrade project. Field data are presented and interpreted to demonstrate how the embankments performed during construction in both vacuum and non-vacuum areas. © ASCE 2014.
Jozi, BJ, Dackermann, U, Braun, RB, Li, JL & Samali, BS 1970, 'Application and improvement of conventional stress-wave-based non-destructive testing methods for the condition assessment of in-service timber utility poles', Proceedings of the 23rd Australasian Conference on the Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, Southern Cross University, Byron Bay, Australia, pp. 1197-1202.
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Timber utility poles represent a significant part of Australia’s infrastructure for power distribution andcommunication networks. Due to their advanced age, significant efforts are undertaken to preventutility lines from failure. However, the lack of reliable tools for assessing the condition of in-servicepoles seriously jeopardizes the maintenance and asset management. Non-destructive testing (NDT)methods based on stress wave propagation can potentially offer simple and cost-effective tools for thecondition assessment of in-service timber poles. Based on the impact direction and location, mainlytwo wave types can be excited in a pole, i.e. longitudinal and bending waves. A conventional stresswave-based method that analyses longitudinal waves is the Sonic Echo (SE) method; and a typicalsignal processing method for the analysis of bending waves (BW) is the Short Kernel Method (SKM).In this paper, firstly, the application of the conventional SE method and the BW method with SKMdata analysis is investigated for the condition assessment of timber poles from a signal processingperspective. Secondly, to improve limitations of the current methods, the application of a multisensorsarray is proposed for more reliable and accurate results. The new method is validated onnumerical data of a timber pole modelled with both isotropic and orthotropic material properties.
Khabbaz, H & Fatahi, B 1970, 'A critical and comparative review of ballasted and slab tracks: Where are we heading?', Civil-Comp Proceedings, International Conference on Railway Technology: Research, Development and Maintenance, Civil-Comp Press, France.
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High speed rail (HSR) is currently an experienced rail transport system, which has been recognised to deliver real benefits against road and air transportation. This paper highlights the geotechnical problems involved with HSR on ballasted tracks and how slab tracks can overcome these issues. There are many geotechnical issues surrounding the performance of high-speed trains on ballasted railway tracks. A number of noticeable issues include critical velocity effects, track vibration and large settlement due to ballast degradation. In comparison to ballasted tracks, slab tracks reduce the construction height, reduce track maintenance, reduce the wear down of rails, provide better riding comfort at high speeds, provide higher availability, reduce vibration and secondary airborne noises, improve load distribution, provide high lateral and longitudinal track stability and eliminate problems with vegetation control, which is essential for a rail track structure. Accordingly, many railway experts have concluded that it is time to say goodbye to the ballasted tracks. Based on several case studies, laboratory results and validated numerical analysis, this paper clearly elaborates that if ballasted tracks are designed and stabilised properly, they will be cost effective and can well-perform under dynamic loads of high speed rails.
Khabbaz, H, Lin, EX & Fatahi, B 1970, 'A Parametric Study on Shoring Structures with Multi-Row Anchors in Layered Soil', Earthwork Project Management, Slope Stability Analysis, and Wave-Based Testing Techniques, Geo-Hubei 2014 International Conference on Sustainable Civil Infrastructure, American Society of Civil Engineers, China, pp. 81-88.
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This paper examines two numerical methods commonly used in shoring design, namely the beams on elastic foundation method using WALLAP and the finite element method (FEM) using PLAXIS. Numerous design parameters are also investigated to study the effects of the parametric variations on each method. The shoring model analyzed in this study is based on a deep excavation project in the Sydney central business district. One of the significant findings of this study was that the results obtained from both WALLAP and PLAXIS showed marginal numerical errors, which, in turn, need to be examined closely. Generally, the beams on elastic foundation method are more conservative than the FEM. In comparison with the FEM, the soil modulus has more significant effects than the shear strength parameters in the beams on elastic foundation method. Moreover, the resulting shear forces, bending moments, and lateral displacements of the shoring are less sensitive to the variation of the soil friction angle than the cohesion. The findings of this study can be taken into consideration by practicing civil engineers when designing appropriate shoring systems in urban areas. © ASCE 2014.
Khorsandnia, N, Valipour, H, Foster, S & Crews, KI 1970, '1D Frame Element Formulation For Analysis Of Layered Composite Beams', Proceedings of the 23rd Australasian Conference on the Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, Southern Cross University, Byron Bay, Australia, pp. 795-800.
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In this paper a numerical model for non-linear analysis of layered composite beams is developed. It
takes advantage of an efficient 1D frame element with forced-based formulation. The developed
element is equipped with lumped translational springs at the nodal points to model the partial shear
interaction between the layers. Also, the proposed FE model can capture the material non-linearities as
well as non-linear shear-slip behaviour of connections between the layers. The sections of frame
element are discretised into fibres and the stiffness matrix of each section can be determined by
integrating the stiffness of fibres over the section depth based on Navier-Bernoulli hypothesis. The
superior performance of the developed FE model for capturing the behaviour of composite beams was
demonstrated by comparing the numerically predicted results with experimental data. The proposed
model can efficiently capture the global response (i.e. load vs deflection, slip, strain and stress) of the
composite beams up to failure with adequate accuracy.
Le, TM, Fatahi, B & Khabbaz, H 1970, 'Numerical solution to predict visco-plastic model parameters of soft clay during excess pore water pressure dissipation', NUMERICAL METHODS IN GEOTECHNICAL ENGINEERING, VOL 1, European Conference on Numerical Methods in Geotechnical Engineering, Taylor and Francis Group, Delft, the Netherlands, pp. 175-180.
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The elastic visco-plastic model with non-linear creep function may describe the long termbehavior of clayey soils more accurately. However, it is a challenging task to determine the parameters of the non-linear creep function using conventional oedometer data. This paper presents a numerical method to determine several model parameters simultaneously, while adopting consolidation data during excess pore water pressure dissipation by applying an advanced optimization tool embedded in MATLAB. Crank-Nicholson finite difference procedure is adopted to solve the partial differential equations of the consolidation equation in combined with the non-linear elastic visco-plastic model. As a result, the time dependent strain and excess pore water pressure dissipation in one dimensional compression are computed simultaneously. In this paper, a case study is presented to evaluate and validate the proposed method. © 2014 Taylor & Francis Group.
Li, J, Wu, C, Hao, H & Su, Y 1970, 'Numerical analysis of uniaxial compression and four bending tests of ultra-high preformance reinforced concrete', 6th International Conference on Protection of Structures against Hazards, Tianjin.
Li, JC, Li, Y, Askari, M & Ha, QP 1970, 'Future Intelligent Civil Structures: Challenges and Opportunities', Proceedings of the International Symposium on Automation and Robotics in Construction (IAARC), 31st International Symposium on Automation and Robotics in Construction, International Association for Automation and Robotics in Construction (IAARC), Sydney, pp. 72-79.
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An intelligent civil structure offers ultimate protection to its structure, contents and occupants in terms of safety and functionality against undesired dynamic loadings and structural deficiency. In this paper, the concept of the future intelligent civil structure featuring self-adaptive, selfprognostic, self-sensing, self-powering and self-repairing abilities, is proposed. A decade research efforts from Centre for Built Infrastructure Research, University of Technology Sydney, towards the development and concept proof of such intelligent structure is reviewed.
Li, Y & Li, J 1970, 'Base isolator with variable stiffness and damping: design, experimental testing and modelling', Proceedings of the 23rd Australasian Conference on the Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, Southern Cross University, Byron Bay, Australia, pp. 913-918.
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Vulnerability in base isolation system of civil structures originated from passive nature of the rubber material raises the urgency of developing smart base isolation system with adaptive and controllable properties, i.e. variable stiffness and damping. To address this issue, this paper presents comprehensive investigations on a novel adaptive base isolator, including design, experimental testing and dynamic modelling. Smart rubber with field-dependent modulus and damping property is incorporated into the laminated base isolator design. Experimental testing is conducted utilising an advanced shake table facility to examine its performance under cycling loading. Results show that the adaptive base isolator possesses a stiffness increase of more than 16 times and damping ratio between 10% and 27%. With such features, it can be developed into a smart base isolation system to protect civil structures against any type of earthquake. Results also show that this device has high nonlinear hysteresis, i.e. shear stiffening behaviour. A mechanical model is thus required to describe the complex behaviour of new adaptive base isolator. A new strain stiffening element is proposed for this purpose. Comparison between the model and the experimental data verifies the fidelity and effectiveness of the proposed model.
Li, Y, Li, J & ASME 1970, 'DEVELOPMENT AND MODELING OF A HIGHLY-ADJUSTABLE BASE ISOLATOR UTILIZING MAGNETORHEOLOGICAL ELASTOMER', PROCEEDINGS OF THE ASME CONFERENCE ON SMART MATERIALS, ADAPTIVE STRUCTURES, AND INTELLIGENT SYSTEMS - 2013, VOL 1, Conference on Smart Materials, Adaptive Structures and Intelligent Systems, ASME, Snowbird, Utah, USA, pp. 1-8.
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This paper presents a recent research breakthrough on the development of a novel adaptive seismic isolation system as the quest for seismic protection for civil structures, utilizing the field-dependent property of the magnetorheological elastomer (MRE). A highly-adjustable MRE base isolator was developed as the key element to form smart seismic isolation system. The novel isolator contains unique laminated structure of steel and MRE layers, which enable its large-scale civil engineering applications, and a solenoid to provide sufficient and uniform magnetic field for energizing the field-dependent property of MR elastomers. With the controllable shear modulus/damping of the MR elastomer, the developed adaptive base isolator possesses a controllable lateral stiffness while maintaining adequate vertical loading capacity. Experimental results show that the prototypical MRE base isolator provides amazing increase of lateral stiffness up to1630%. Such range of increase of the controllable stiffness of the base isolator makes it highly practical for developing new adaptive base isolation system utilizing either semi-active or smart passive controls. To facilitate the structural control development using the adaptive MRE base isolator, an analytical model was developed to stimulate its behaviors. Comparison between the analytical model and experimental data proves the effectiveness of such model in reproducing the behavior of MRE base isolator, including the observed strain stiffening effect. Copyright © 2013 by ASME.
Moshiri, F, Gardner, AP, Erkmen, E, Jarman, R & Khabbaz, H 1970, 'Enhancing Industry Exposure, Discovery-Based and CooperativeLearning in Mechanics of Solids', Australasian Association for Engineering Education Annual Conference 2014, Australasian Association for Engineering Education Annual Conference 2014, School of Engineering & Advanced Technology, Massey University, Turitea Campus, Palmerston North 4442, Wellington, NZ.
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BACKGROUND Mechanics of Solids is a second year undergraduate subject, undertaken by both Civil and Mechanical engineering students at the University of Technology, Sydney (UTS). Mechanics of Solids has been delivered for many years in a traditional format with lectures and problem solving tutorials. As part of a national Australian project “Enhancing Industry Exposure in Engineering Degrees”, UTS in partnership with other universities and industry partners in Australia has sought industry involvement to engage students with the real-world challenges of engineering practice. PURPOSEThe main objective of this project is to design, develop and implement learning modules in Mechanis of Solids that integrate industry exposure to provide context for the concepts included in this subject. DESIGNThe project consisted of six guest lectures by industry representatives on topics related to typical Mechanics of Solids subject matter and two seminars on using MDSolids software.Students completed a collaborative assignment aligned with one of the industry presentations. Their reports and presentations were assessed on assessment criteria which included contextual understanding, judgement, effective collaboration and creativity, and their perceptions were captured to evaluate the impact of industry engagement in this subject.RESULTSOne of the major benefits of this project was students’ better understanding of engineering practice. There were also positive effects on students’ motivation for learning engineering. CONCLUSIONS This paper reports the major findings, outcomes and challenges for implementing enhancing industry exposure approach in Mechanics of Solids subject at UTS. The main finding of this research concluded that this project is very valuable to both students as it promotes exposure to real-world engineering challenges. The students’ exposure to real and substantive challenges improves their contextual understanding, plus their judgement,...
Nguyen, HH, Khabbaz, H, Fatahi, B, Vincent, P & Marix-Evans, M 1970, 'Sustainability considerations for ground improvement techniques using controlled modulus columns', PROCEEDINGS OF THE 2014 AGS SYMPOSIUM, AGS Symposium on Resilient Geotechnics, The Australian Geomechanics Society, AUSTRALIAN NATIONAL MARITIME MUSEUM, DARLING HARBOUR, NSW AUSTRALIA, pp. 170-170.
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Sustainability is becoming an ever more important consideration for the selection of ground improvement methods on construction projects around the world. When considering this criterion, the controlled modulus column (CMC) technology emerges as one of the relatively novel technologies that are capable to deliver valuable and sustainable outcomes. CMC installation is a vibration free process and produces very limited soil cuttings, making CMC suitable for improvement of soft ground, contaminated sites and ones adjacent to sensitive structures. Besides, CMC uses grout only without the use of steel reinforcement; hence carbon footprint estimated for CMC is generally lower than those for traditional piling techniques. Besides these valuable aspects, it is believed that this technology can still be advanced to contribute more to the sustainable development, owing to ongoing research works and practical experience. This paper summarises the key sustainability aspects of using CMC technology and highlights some potential aspects for further development. Future research directions are discussed to enhance sustainable design practice. These include general discussions on the issues of economic design with trial field tests, the use of recycled industrial by-products for grout mix, improved design, maximising the resiliency of structures and the energy consumption. The CMC installation effects on the surrounding soils and environment are also discussed sensibly in this paper.
Nguyen, L, Fatahi, B & Khabbaz, H 1970, 'Modelling Behaviour of Cemented Clay Capturing Cementation Degradation', Ground Improvement and Geosynthetics, Geo-Shanghai 2014, American Society of Civil Engineers, Shanghai, China, pp. 168-177.
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This paper presents a constitutive model - referred to as the Cemented Cam Clay (CCC) model - to precisely simulate the cementation degradation of cement-treated clays. Various laboratory experiments show that the effect of cementation gradually diminishes as the confining pressure increases (particularly at high effective confining pressures) due to breakdown of cementation bonds. The main concepts and formulations of the CCC model, including elasto-plastic stress-strain relationships, are presented within the framework of the critical state concept and inspired by the Modified Cam Clay (MCC) model. The special characteristic of the proposed model includes a modified mean effective stress capturing cementation degradation. In addition, the failure envelope is formulated to describe the beneficial effect of cementation at low mean effective pressure range, while it merges with the Critical State Line of reconstituted cement-clay mixture as the confining pressure continues to increase. The performance of the proposed model is evaluated against triaxial test results from cement-treated Aberdeen soil. The model predictions provide good agreement with triaxial test results, particularly at high effective confining pressures. © ASCE 2014.
Nimbalkar, S & Indraratna, B 1970, 'Numerical and analytical modeling of particle degradation', Computer Methods and Recent Advances in Geomechanics - Proceedings of the 14th Int. Conference of International Association for Computer Methods and Recent Advances in Geomechanics, IACMAG 2014, International Conference of the International Association for Computer Methods and Advances in Geomechanics, CRC Press, Kyoto, Japan, pp. 261-266.
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Large cyclic loads are nowinevitable due to an increased demand for freight and public transport. The ballast layer subjected to these repeated traffic loads in a real track environment undergoes excessive deformation and degradation. Ballast degradation is influenced by various factors including the amplitude and number of load cycles, confining pressure, frequency, the angularity as well as fracture strength of individual grains. Given the complexities of the behaviour of the rail track, the current track analysis techniques are overly simplified. Considering this, an elasto-plastic constitutive model of a composite track is proposed. The largescale laboratory tests are simulated in a numerical model and the results are then analyzed to better understand the distribution of displacements and stresses inside the ballast layer. The advantages of the elasto-plastic finite element simulations when compared to conventional analytical methods used by practitioners that are primarily based on a linear elastic approach are demonstrated. © 2015 Taylor & Francis Group, London.
Oduro, SD, Metia, S, Duc, H, Hong, G & Ha, QP 1970, 'Prediction of NOx Vehicular Emissions Using On-Board Measurement and Chassis Dynamometer Testing', Proceedings of the International Symposium on Automation and Robotics in Construction (IAARC), 31st International Symposium on Automation and Robotics in Construction, International Association for Automation and Robotics in Construction (IAARC), Sydney Australia, pp. 584-591.
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Motor vehicles' rate models for predicting emissions of oxides of nitrogen (NOX) are insensitive to their modes of operation such as cruise, acceleration, deceleration and idle, because these models are usually based on the average trip speed. This study demonstrates the feasibility of using other variables such as vehicle speed, acceleration, load, power and ambient temperature to predict NOX emissions. The NOX emissions need to be accurately estimated to ensure that air quality plans are designed and implemented appropriately. For this, we propose to use the non-parametric multivariate adaptive regression splines (MARS) to model NOX emission of vehicle in accordance with on-board measurements and also the chassis dynamometer testing. The MARS methodology is then applied to estimate the NOX emissions. The model approach provides more reliable results of the estimation and offers better predictions of NOX emissions. The results therefore suggest that the MARS methodology is a useful and fairly accurate tool for predicting NOX emission that may be adopted by regulatory agencies in understanding the effect of vehicle operation and NOX emissions.
Parsa-Pajouh, A, Fatahi, B, Khabbaz, H & Vincent, P 1970, 'Evaluating Proposed Solutions for Equivalent Plane Strain Modeling of PVD Assisted Preloading', Advances in Transportation Geotechnics and Materials for Sustainable Infrastructure, Geo-Hubei 2014 International Conference on Sustainable Civil Infrastructure, American Society of Civil Engineers, China, pp. 9-16.
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In this study, a numerical code has been developed using free lossless audio codec (FLAC) 2-D to model the prefabricated vertical drain (PVD) assisted preloading process considering the smear zone, and evaluate the efficiency of the proposed equations for the conversion of permeability coefficient from axisymmetric state to plane-strain condition. A laboratory PVD assisted preloading test has been conducted employing a fully instrumented large Rowe cell to verify the developed numerical code. The results of the numerical plane-strain and axisymmetric simulations have been compared using four methods of permeability conversion from axisymmetric to plane-strain condition. © ASCE 2014.
Quang, NK, Ha, QP & Hieu, NT 1970, 'FPGA sensorless PMSM drive with adaptive fading extended Kalman filtering', 2014 13th International Conference on Control Automation Robotics & Vision (ICARCV), 2014 13th International Conference on Control Automation Robotics & Vision (ICARCV), IEEE, Singapore, pp. 295-300.
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This paper addresses the design and implementation
of an Adaptive Fading Extended Kalman Filter (AF-EKF) for
the sensorless Permanent Magnet Synchronous Motor (PMSM)
on a Field Programmable Gate Array (FPGA) chip. The rotor
position and speed of the motor are estimated by the implemented
AF-EKF and their estimates are then used in vector control
of the PMSM. In conventional Kalman filtering, abrupt state
changes may not be tracked adequately since sudden variations
may seriously affect the auto-correlation Gaussian property of
white noise in the filter residuals. For this, the AF-EKF has
been developed to recover the estimation results in events of
frequent and sharp state jumps. The AF-EKF is, therefore,
a promising estimator for PMSM drives that are subject to
frequently-varying loads speed commands. Here, for realization of
the PMSM sensorless control using the system-on-programmablechip
technology, high-speed arithmetic functions and pipelining
are employed in the FPGA implementation. The finite state
machine method is also used to facilitate the execution timing
and chip design. The co-simulation of Modelsim/Simulink shows
effectiveness of the proposed chip-based AF-EKF PMSM speed
estimation.
Schluessel, M, Shrestha, R & Crews, K 1970, 'Acoustic performance of timber and timber-concrete composite floors', WCTE 2014 - World Conference on Timber Engineering, Proceedings.
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A major problem in light-weight timber floors is their insufficient performance coping with impact noise in low frequencies. There are no prefabricated solutions available in Australia and New Zealand. To rectify this and enable the implementation of light-weight timber floors, a structural floor was designed and built in laminated veneer lumber (LVL). The floor was evaluated in a laboratory setting based on its behaviour and then modified with suspended ceilings and different floor toppings. Twenty-nine different floor compositions were tested. The bare floor could not reach the minimum requirement set by the Building Code of Australia (BCA) but with additional layers, a sufficient result of R'w+Ctr53 dB and L'nT,w+ CI50 dB was reached. Doubling of the concrete mass added a marginal improvement. With concrete toppings and suspended ceiling it is possible to reach the goal in airborne and impact sound insulation. The best result was achieved by combining of additional mass and different construction layers. KEYWORDS: Acoustics, acoustic insulation, light weight floor, timber floor, timber-concrete composite.
Shrestha, R & Crews, K 1970, 'Development of engineered bamboo', WCTE 2014 - World Conference on Timber Engineering, Proceedings, World Conference on Timber Engineering (WCTE), Quebec City, Canada.
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Bamboo is one of the fastest growing plants and has mechanical properties similar to timber. Application of bamboo in construction is, however, limited to low cost housing and temporary structures due to a number of growth characteristics such as irregular shapes, hollow circular cross-sections, etc. To overcome these limitations in bamboo, an experimental study was undertaken to investigate the potential of developing an engineered bamboo product by cutting bamboo into smaller strips and gluing them together into rectangular cross-sections. Results of the tests showed that higher strength and stiffness and much lower variation in these properties, compared to natural bamboo, can be achieved when bamboo is fabricated into such an engineered product.
Shrestha, R & Crews, KI 1970, 'Development of engineered bamboo using a low-tech method', Proceedings of the 23rd Australasian Conference on the Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, Southern Cross University, Byron Bay, Australia, pp. 613-618.
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Bamboo is one of the fastest growing plants and has mechanical properties similar to softwood timber. Bamboo has been commonly used for many years as a traditional construction material for low rise houses, foot bridges, roofs and construction platforms, especially in Asia and Latin America. The main reasons for the popularity of bamboo in construction can be attributed to its low cost, general availability locally and adequacy of simple, local tools and skills for fabrication.Application of bamboo in construction is, however, normally limited to low cost housing and temporary structures due to a number of factors including irregular shapes, hollow circular cross-sections and durability issues. This paper presents the results of an investigation into production of an engineered bamboo product using a low tech method. Bamboo culms were cut into smaller strips and were re-constituted into rectangular beam sections by gluing. Such a process overcomes the presence of the inherent hollow core and randomises the inter-nodes and other growth characteristics found in natural bamboo – in much the same way that engineered wood products such as plywood and LVL are produced. Flexural properties of the manufactured engineered bamboo were then compared with natural bamboo. Higher flexural strength and stiffness and lower variation in these properties, compared to natural bamboo, were achieved by re-constituting the bamboo into a manufactured product.
Shrestha, R, Lewis, K & Crews, KI 1970, 'Introduction to cross laminated timber and development of design procedures for Australia and New Zealand', Proceedings of the 23rd Australasian Conference on the Mechanics of Structures and Materials (ACMSM23), Australasian Conference on the Mechanics of Structures and Materials, Southern Cross University, Byron Bay, Australia.
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Cross-laminated timber (CLT) is an engineered wood product which is gaining popularity in Europe and North America as a sustainable alternative to concrete and steel construction in commercial and multi-residential buildings. CLT is a panel type product made up of 3 or more layers of timber boards each layer running in orthogonal directions and can be used as wall or floor panels.Investment in sustainable softwood plantations over the past few decades has meant that there is now an abundant supply of renewable timber resources ready to be utilized, to produce light weight buildings with low carbon footprints, smaller foundations and transport requirements and increased speed and ease of construction.There is an increasing interest within the construction industry in Australia to start producing CLT panels. Research at the University of Technology Sydney has shown that CLT panels manufactured within Australia from Australian grown timber can compete with international products. CLT floor panels have been found to have significant strength to weight benefits, the potential to be used as two-way spans, higher than predicted char ratios and can comply with Building Code of Australia (BCA) requirements for acoustic design.This paper presents an overview of research and work completed to date, and a discussion of issues that have been identified and addressed to establish design procedures for CLT to meet Australian building standards and code requirements.
Sinha, A & Wang, J 1970, 'An implementation of the path integrator mechanism of head direction cells for bio-mimetic navigation', 2014 International Joint Conference on Neural Networks (IJCNN), 2014 International Joint Conference on Neural Networks (IJCNN), IEEE, Beijing, pp. 1984-1991.
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© 2014 IEEE. Head direction cells are thought to be an integral part of the neural navigation system. These cells track the agent's current head direction irrespective of the host's location. In doing so, they process a combination of inputs: angular velocity and visual inputs are major effectors; to correctly encode the agent's current heading. There are close to fifteen models of head direction cell systems found in literature today. Very few of these models have been implemented for bio-mimetic navigation in robots. In this paper, we describe an implementation of the head direction cell system on the robot operating system (ROS) robotic platform as a first step towards a bio-mimetic navigation system for Willow Garage's personal robot 2 (PR2) robot.
Tennakoon, N, Indraratna, B & Nimbalkar, S 1970, 'Impact of Ballast Fouling on Rail Tracks', Proceedings of the Second International Conference on Railway Technology: Research, Development and Maintenance, The Second International Conference on Railway Technology: Research, Development and Maintenance, Civil-Comp Press, Ajaccio, Corsica, France, pp. 1-11.
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© Civil-Comp Press, 2014. Ballast fouling is understood as major cause of track deterioration in many countries over the world. It decreases the drainage and load bearing capacity of the ballast layer. A series of large scale hydraulic conductivity tests were conducted with different proportions of fouling to access the drainage capacity of the track. A numerical analysis was conducted using SEEP/W to quantify the drainage capacity of ballast under different degrees of fouling. Subsequently, track drainage classification in relation to the degree of fouling, which is a very useful tool for practical engineers, is presented in this paper. The analysis showed that both the location and extent of fouling played an important role when assessing the overall drainage capacity of track. In order to establish the relationship between the extent of fouling and the associated strength-deformation properties, a series of large scale monotonic triaxial tests were carried out for different levels of fouling for three different confining pressures. Based on the laboratory findings, a novel empirical relationship between the peak deviator stress and VCI has been proposed to assist the practitioner in their preliminary track condition assessment. By considering drainage and strength aspects, a critical level of fouling to assist in track maintenance planning has been considered.
Thomas, D, Ding, G & Crews, K 1970, 'Sustainable timber use in residential construction: perception versus reality', Energy and Sustainability V, ENERGY AND SUSTAINABILITY 2014, WIT Press, Kuala Lumpur, Malaysia, pp. 399-410.
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Close to 90% of new project homes in NSW, Australia are constructed with reinforced concrete flooring and brick veneer envelope whereas many traditional Australian homes were built of timber floor structures with timber walls and cladding. The adoption of concrete and brick homes originated from a perceived advantage of longevity, low maintenance and thermal comfort. Innovation in wood treatments, wood protection and insulation have provided solutions to these issues so that timber is once again a viable option with added benefits such as environmental sustainability and erection speed. This paper reviews literature and analyses the results of a home occupants survey on the perception of timber use in new homes in NSW, Australia. It also investigates the comparative performance of a timber veneer/structural timber home to a concrete floor/brick veneer home to evaluate whether perception of timber performance matches reality. This paper highlights Australian homeowners reluctance to use timber as a sustainable building product for homes even when they are willing to pay for a more environmentally sustainable home. It also discusses the time and environmental advantages of a timber home over a concrete and brick home based on the results of a test case study.
Tran, H-D, Ha, QP & Dang, Q-V 1970, 'Guaranteed cost static output feedback for networked control systems', 2014 13th International Conference on Control Automation Robotics & Vision (ICARCV), 2014 13th International Conference on Control Automation Robotics & Vision (ICARCV), IEEE, Signapore, pp. 1267-1272.
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This paper is concerned with the guaranteed cost
static output feedback (SOF) control for a networked control
system (NCS) in imperfect conditions. First, by analyzing the
sampling process in connection with network-induced delays and
consecutive data packet dropouts and by introducing a new delay
function, we formulate such a NCS as a continuous time delay
system with the practical assumption that network delays and
consecutive dropouts are bounded. Then, based on the delaydependent
approach, sufficient conditions for the existence of a
guaranteed cost SOF controller in the NCS are obtained via
a set of non-convex matrix inequalities. A cone complementary
linearization (CCL) algorithm is used to solve these inequalities to
determine a sub-optimal controller that minimizes the guaranteed
cost of the NCS. Simulation results are shown to demonstrate the
effectiveness of the proposed method.
Tri Tran & Ha, QP 1970, 'Dependable control systems with self-recovery constraint', The 2014 International Conference on Control, Automation and Information Sciences (ICCAIS 2014), 2014 International Conference on Control, Automation and Information Sciences (ICCAIS), IEEE, Gwangju, South Korea, pp. 87-92.
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© 2014 IEEE. A novel constrained-state feedback control design method for duty-standby controllers of a dependable control system is presented in this paper. The dependable control system is a replacement for the classical reliable control system which has been developed for wired and analog systems. As an alternative to the control summation in reliable control systems, only one controller is active at any one time in a dependable control system. This will make it compatible with the duty-standby architecture of dependable computer systems that run the control algorithm. The automated managing of duty-standby controllers is challenging, especially in wireless sensor and actuator networks, owing to the scarcity of both information and processing resources. The solutions proposed in this paper are effective and feasible, as taking into account both state- and control-incremental constraints, and simply involving a static state-feedback strategy to minimize the computational demand in implementations. The state feedback gains are synthesized to fulfill the strict requirement on the two incremental constraints. As a result of that, the duty-standby controllers will be able to operate independently, while assuring the closed-loop system stability with a newly introduced self-recovery constraint. For a dependable control system, the employed self-recovery constraint is a quadratic constraint with respect to the control and state increments.
Vakhshouri, B & Nejadi, S 1970, 'Limitations and Uncertainties in the Long-Term Deflection Calculation of Concrete Structures', Vulnerability, Uncertainty, and Risk, Second International Conference on Vulnerability and Risk Analysis and Management (ICVRAM) and the Sixth International Symposium on Uncertainty, Modeling, and Analysis (ISUMA), American Society of Civil Engineers, University of Liverpool, UK, pp. 535-546.
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© 2014 American Society of Civil Engineers. There is no distinctive boundary in RC members when the short-term deflection ends and long term begins. Simplified procedures for predicting deflections in design codes are not compatible with actual deflection under service loads, especially in sensitive elements such as floor slabs. Design codes generally predict the time-dependent deflection by multiplying an empirical amplification factor by an instantaneous deflection. Despite the negligible difference in instantaneous and short-term deflection, the calculated value for long-term deflection that is due to decrease in stiffness overtime due to the inelastic deformation of concrete shrinkage and creep, is sometimes significantly less than the actual deflection. In this paper, simplified calculations for the ratio of long-term to short-term deflection in codes and some empirical works have been compared. Based on the comparison between simplified methods and data obtained from experimental investigations of Gilbert and Guo (2005), it is evident that the long-term/ short-term ratio is sometime significantly beyond the range of codes of practice.
Wonschik, C-R, Brennan, J, Ding, G, Heilmann, A & Vessalas, K 1970, 'Implications of Legal Frameworks on Construction and Demolition Waste Recycling a Comparative Study of the German and Australian Systems', Proceedings of the International Symposium on Automation and Robotics in Construction (IAARC), 31st International Symposium on Automation and Robotics in Construction, International Association for Automation and Robotics in Construction (IAARC), Sydney, Australia, pp. 523-530.
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This comparative study between German and Australian legislation demonstrates that legal frameworks impact on the way in which recycling systems work. Both Australia and Germany operate as Federations and the autonomy of states influences common federation wide practices and standards. In Germany's case however, it is obliged to comply with European Union guidelines which result in German federal legislation being binding for all German states and to common industry practices across all of Germany. Purely industry regulated systems are not always sufficient to cater for societal and environmental needs, and political intervention can sometimes be necessary to achieve desired outcomes. The construction and demolition (C&D) waste recycling industry is a good example. In Australia C&D waste recycling is mostly industry regulated, while the state has greater influence in Germany. A statistical analysis illustrates legislative impact on recycling outcomes. Nonetheless, any legislative efforts can also have effects contrary to the intended ones. A study of such cases is conducted and other influencing factors also considered. In conclusion, the study outlines the importance of interstate coordination and regulation; and the need for the incorporation of industry requirements and other potentially influencing factors into the legal frameworks in order to meet desired outcomes.
Xu, J, Wu, C, Xiang, H, Su, Y, Li, Z-X, Fang, Q, Hao, H, Liu, Z, Zhang, Y & Li, J 1970, 'Experimental study on the response of ultra-high preformance reinforced concrete columns under blast loading', 6th International Conference on Protection of Structures against Hazards, Tianjin.
Yu, Y, Li, Y & Li, J 1970, 'A New Hysteretic Model for Magnetorheological Elastomer Base Isolator and Parameter Identification Based on Modified Artificial Fish Swarm Algorithm', Proceedings of the International Symposium on Automation and Robotics in Construction (IAARC), 31st International Symposium on Automation and Robotics in Construction, International Association for Automation and Robotics in Construction (IAARC), Sydney, pp. 176-183.
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Magnetorheological elastomer (MRE) base isolator is a new semi-active control device that has recently acquired more attention. This paper proposes a new model for MRE base isolator to portray the nonlinear hysteresis between generated force and the displacement. In this model, a hyperbolic expression is proposed to compare with the classical Bouc-Wen model, which includes internal dynamics represented by a nonlinear differential equation. For the identification of model parameters, a modified artificial fish swarm algorithm is adopted using the experimental force-displacement/velocity data under different testing conditions. In this algorithm, a self-adaptive method for adjusting the algorithm parameters is introduced to improve the result accuracy. Besides, the behaviours in the algorithm are simplified to descend the algorithmic complexity. Parameter identification results are included to demonstrate the accuracy of the model and the effectiveness of the identification algorithm.
Yu, Y, Li, Y & Li, J 1970, 'A Novel Strain Stiffening Model for Magnetorheological Elastomer Base Isolator and Parameter Estimation Using Improved Particle Swarm Optimization', Proceedings of the 6th edition of the World Conference of the International Association for Structural Control and Monitoring (IACSM), Sixth World Conference on Structural Control and Monitoring (6WCSCM), International Center for Numerical Methods in Engineering (CIMNE), Barcelona, Spain.
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In order to fully utilize the advantages of magnetorheological elastomer (MRE) base isolator for seismic protection of civil structures, a high fidelity model should be established to characterize its nonlinear hysteresis for its implementation in structural control. In this paper, a novel strain stiffening model is developed to capture this unique characteristic. In this model, a strain stiffening component, which described the unique viscos-elastic behavior of the device, is incorporated with a Voigt element, which portrays the solid-material behavior. The new model, as an attractive feature, maintains a relationship between the isolator parameters and physical force-displacement nonlinear phenomenon and decreases the complexity in other existing models. In addition to the proposed model, an improved optimization algorithm based on particle swarm optimization (IPSO) is designed to identify the model parameters by utilizing experimental force-displacement-velocity data acquired from various loading conditions. In this new algorithm, the mutation operation in genetic algorithm is utilized for helping the model solution avoiding the local optimum. The superiority of the proposed model and parameter solving algorithm is validated by comparing them with the classical Bouc-Wen model and other optimization algorithms through the error analysis, respectively. The comparison results show that the proposed model can exactly predict the force-displacement and force-velocity responses at both small and large displacements, and has a smaller root-mean-square (MSE) error than the Bouc-Wen model. Compared with other optimization algorithm, the IPSO not only has a faster convergence rate, but also obtains the satisfactory parameters identification results.
Yu, Y, Li, Y & Li, J 1970, 'Parameter Identification Of An Improved Dahl Model For Magnetorheological Elastomer Base Isolator Based On Enhanced Genetic Algorithm', Proceedings of the 23rd Australasian Conference on the Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, Southern Cross University, Byron Bay, Australia, pp. 931-936.
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In view of the problems of high nonlinearity and multiple parameters in existing models of magnetorheological elastomer (MRE) base isolator, this paper proposes an improved Dahl model and an enhanced genetic algorithm (GA) for model parameter identification. In this model, the Dahl hysteresis operator is employed to depict the Coulomb force to avoid the estimation of many parameters and this model can perfectly capture the hysteretic behavior of the MRE base isolator at both small and large displacements. To improve the searching efficiency of identification process, adaptive crossover and mutation operators are introduced into the GA to avoid the algorithm falling into the local optimum, achieving faster convergence rate for optimal solutions. Furthermore, an appropriate stopping criterion is designed to reduce the calculation cost. Testing data from a practical MRE base isolator are utilized to validate the proposed algorithm with satisfactory parameter identification results.
Zhang, Y, Zhao, Y, Xiong, R, Wang, Y, Wang, J & Chu, J 1970, 'Spin observation and trajectory prediction of a ping-pong ball', 2014 IEEE International Conference on Robotics and Automation (ICRA), 2014 IEEE International Conference on Robotics and Automation (ICRA), IEEE, Hong Kong, China, pp. 4108-4114.
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For ping-pong playing robots, observing a ball and
predicting a ball’s trajectory accurately in real-time is essential.
However, most existing vision systems can only provide ball’s
position observation, and do not take into consideration the
spin of the ball, which is very important in competitions. This
paper proposes a way to observe and estimate ball’s spin in
real-time, and achieve an accurate prediction. Based on the
fact that a spinning ball’s motion can be separated into global
movement and spinning respect to its center, we construct an
integrated vision system to observe the two motions separately.
With a pan-tilt vision system, the spinning motion is observed
through recognizing the position of the brand on the ball and
restoring the 3D pose of the ball. Then the spin state is estimated
with the method of plane fitting on current and historical
observations. With both position and spin information, accurate
state estimation and trajectory prediction are realized via
Extended Kalman Filter(EKF). Experimental results show the
effectiveness and accuracy of the proposed method.