Aldridge, LP, Vessalas, K, Fernando, K, Costa, MD, Thomas, P & Ray, AS 2011, 'Comparison of durability measures of concrete as a function of cure times', Concrete in Australia, vol. 36, no. 4, pp. 42-47.
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This work forms part of a project for evaluating techniques of estimating concrete durability to improve service life. Here compressive strength, chloride diffusivity, void volume, and sorptivity from water cured concretes were measured at seven, 28 and 56 days to evaluate the concrete durability as a function of curing. It was concluded that while void volume and sorptivity were useful as quality control measures they did not reflect the increase in durability found when concrete was cured. This was in contrast to the chloride diffusivity and compressive strength results which showed marked differences during the curing of the concrete. For this study four concrete mixes were prepared using identical compositions of water, sand, and aggregates and having the same amount of cementitious materials with four different compositions: (1) Ordinary Portland Cement (OPC) (2) OPC with 20% replacement of a commercial fly ash (3) OPC with 40% replacement of the same fly ash, and (4) OPC with 20% replacement by pitchstone fines. Pitchstone fines are a waste product made during the production of expandable perlite aggregate which previous work has shown to act as a supplementary cementitious material.
Fatahi, B, Engelbert, D, Mujic, S & Khabbaz, H 2011, 'Effects of preloading on soft clay improvement using Deep Soil Mixing', Australian Geomechanics Journal, vol. 46, no. 3, pp. 63-71.
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Poor performing soils, particularly soft clays, are more prevalent around lakes and coastal environments, where demand for construction is generally higher. It is therefore critical that suitable ground improvement techniques be developed and refined to ensure these sites perform satisfactorily under applied structural loads. There is a clear trend in geotechnical construction to further develop technologies such as Deep Soil Mixing (DSM), using cement, lime, fly ash or bottom ash, with an aim to improve the mechanical properties of problematic soils. In this study, the influence of surcharge (10 kPa to 120 kPa) applied during curing on soil-cement columns is investigated using two different clay types, namely kaolinite and bentonite. Preload provides confinement and pre-compression during curing, which in turn increases the bearing capacity of the treated ground. The results of unconfined compressive strength tests are analysed to illustrate how the mechanical properties of the clays composed of differing cement content are influenced under varying surcharges applied instantly after mixing. The results indicate that mechanical properties of cement treated soft clays, including strength and stiffness can be enhanced through the application of surcharge immediately after construction, during the curing phase. This could potentially provide a cost effective and environmentally friendly alternative by reducing the required cement content being added to soil to achieve a given strength.
Fatahi, B, Khabbaz, H & Ho, HL 2011, 'Effects of geotextiles on drainage performance of ballasted rail tracks', Australian Geomechanics Journal, vol. 46, no. 4, pp. 91-102.
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Naturally soft soils are mostly found around coastal regions, where the construction of ballasted rail tracks is required to have a more thorough consideration regarding filtration. Any poor filter design on weak ground inevitably leads to a critical change in ballast characteristics. It is noticeable that such a change results in several issues including significant migration of finer particles about the subballast-subgrade interface and the deficiency of subballast filtration. These problems eventually reduce the drainage ability of the rail sub-system and may cause severe damage which can only be remedied by frequent and costly track maintenance. It is therefore important that geosynthetics such as geotextiles are introduced to the rail track system as an additional filter layer, which is able to retain the desirable filtering characteristics. This paper investigates the impact of non-woven geotextiles on filtration behaviour of subballast in the laboratory, while adopting different granular filter (subballast) thicknesses varying from 0 mm to 50 mm. The research findings demonstrate a notable difference in the cumulative fine loss per unit volume within a given period of time between two distinctive tests - with and without geotextiles, thus emphasising the beneficial application of this geosynthetic material. Empirical estimation of permeability and properties of subballast, including grading curves after testing, are carefully carried out and the results are presented in this paper. The results indicate that the thickness of granular subballast can be significantly reduced by including geotextiles. This paper, in turn, evaluates the potential combination of the track substructure and geotextiles to achieve the optimum filter design and more importantly, alleviate the cost of track maintenance.
Fatahi, B, Khabbaz, SH & Basack, S 2011, 'Effects of salinity and sand content on liquid limit and hydraulic conductivity', Australian Geomechanics Journal, vol. 46, no. 1, pp. 67-76.
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Soil conditions of construction sites have become worse than ever due to the overpopulation in the metropolitan areas throughout the world. Likewise, the prevention of environmental risks due to individual activities is one of the most important subjects in the geo-environmental problems. Saline soils may induce several problems in geotechnical engineering projects such as infrastructure embankments, road construction and clay liners. Effect of the various concentrations of sodium chloride (NaCl) on several different soils including bentonite, kaolinite and fine sand mixtures has been evaluated. In addition, influence of salinity and the period of submergence on the hydraulic conductivity of soil samples collected from a certain area of east coast of India was investigated. The results show that the liquid limit of the mixtures generally decreases with an increase in the salt concentration. Liquid limit decreased significantly with an increase in NaCl concentration up to a certain level. However, a further increase in the concentration does not induce any significant decrease in liquid limit. Furthermore, the soil hydraulic conductivity increase with the salt concentration and with increase in the period of submergence, the hydraulic conductivity of the soil increases asymptotically.
Hokmabadi, AS, Fakher, A & Fatahi, B 2011, 'Seismic Strain Wedge Model for analysis of single piles under lateral seismic loading', Australian Geomechanics Journal, vol. 46, no. 1, pp. 31-41.
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One of the most effective methods of analysing a single pile and pile groups under lateral loading is Strain Wedge Model (SWM). SWM has a number of advantages in comparison with traditional p-y curves, but this model could traditionally only be used to analyse piles under monotonie loads. In the present paper, SWM has been modified to consider dynamic lateral loading. Based on this new method, called Seismic Strain Wedge Model (SSWM), a computer code has been developed for lateral analysis of piles. Using this computer code, some case studies have been analysed and the results show good agreement with test data. This paper introduces SSWM as a simple and powerful solution to analyse piles under lateral seismic loading.
HU, H 2011, 'Dynamic Modeling and Its Sliding Controller of MR Shock Absorber under Impact Load', Journal of Mechanical Engineering, vol. 47, no. 13, pp. 84-84.
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An MR shock absorber under impact load is investigated. A single-rod long-stroke impact absorber is developed. Based on Bingham model and its structure of MR damper under impact load, a dynamic model of MR damper under impact load is derived, which is composed of annular damping hole's friction damping force, coulomb damping force, inertia damping force, throttle damping force, structure additional damper force and other friction forces. By applying the least square algorithm, important parameters in the dynamic model are identified. Experimental results confirm the accuracy of the derived and fitted dynamic model. According to its strong nonlinearity, wide frequency range and high peak-value of acceleration characteristics of impact load, an output target tracer using sliding control strategy is designed and simulated on the basis of constructing hardware-in-the-loop platform. The control effects of three control strategies, namely, On-Off strategy, PID strategy and sliding mode control strategy, are compared and analyzed. The results show that the vibration peak value of MR impact absorber under sliding mode control strategy is reduced by 27.33%, and its piston stroke is reduced by 48.75%, thus being the most ideal control effect. ©2011 Journal of Mechanical Engineering.
Hu, Y, Wu, C, Lukaszewicz, M, Dragos, J, Ren, J & Haskett, M 2011, 'Characteristics of Confined Blast Loading in Unvented Structures', International Journal of Protective Structures, vol. 2, no. 1, pp. 21-43.
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Confined blast loading occurs in many scenarios and the effects of confined blast loading may result in more serious damage to buildings due to multiple shock reflections (Shi et al. 2009). However, spherical charges are assumed for all confined explosive-effects computations in modern standards for blast-resistant design such as UFC-3-340-02 (2008) and the soon-to-be published ASCE Standard for the Blast Protection of Buildings (ASCE forthcoming) without consideration of effects of charge shape on the distribution of reflected overpressure and impulse. As confinement is an aggravation factor of explosion effects, analysis and design of infrastructure under critical scenarios of confined blast loading should take the aggravation factor into consideration. This paper is to develop a numerical model for prediction of blast loads inside unvented structures as a result of variation of the charge shape, charge orientation, geometries and volumes of confined chambers. A finite element program, AUTODYN (Century Dynamics, 2003), is utilized extensively to generate a model which is capable of being calibrated with the experimental results conducted by Wu et al. (2010) in external conditions and by Zyskowski et al. (2004) in a confined small box. The calibrated AUTODYN model is then used to conduct parametric studies to analyze the effects of the variation of charge shape, charge orientation, chamber geometry and chamber volume on the peak reflected overpressure and impulse on the walls of the chamber. The quasi-static overpressure for fully confined blast loading is characterized and the simulated results are used to derive the relationships between the quasi-static overpressure and scaled distance for the fully confined blast loading. Discussion is made on characteristics of fully confined blast loading inside chambers.
Ip, KH, Stuart, B, Ray, A & Thomas, P 2011, 'ESEM-EDS Investigation of the Weathering of a Heritage Sydney Sandstone', Microscopy and Microanalysis, vol. 17, no. 2, pp. 292-295.
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AbstractThe degradation of Sydney sandstone used to build the heritage St Mary's Cathedral in Sydney, Australia, has been investigated using environmental scanning electron microscopy combined with energy dispersive X-ray spectroscopy. This technique provided the structural details of the cementing clay and an elemental characterization the sandstone. The observed differences in the elemental composition of the unweathered and weathered sandstones were associated with changes to the clay microstructure upon weathering. The results support the substitution theory that Fe3+ replaces Al3+ in the kaolinite clay component upon weathering. An examination of the impurities present prior to a nonstructural iron removal treatment revealed the presence of minerals that may provide a source of the elements responsible for the substitution process.
Ip, KH, Stuart, BH, Thomas, PS & Ray, A 2011, 'Characterisation of poly(vinyl alcohol)-montmorillonite composites with higher clay contents', POLYMER TESTING, vol. 30, no. 7, pp. 732-736.
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Polymer composites comprised of poly(vinyl alcohol) and montmorillonite with higher clay loadings have been prepared and characterised. The extent of intercalation in the composites was examined over a range of compositions using scanning electron microscopy energy dispersive spectroscopy and x-ray diffraction. The incorporation of an acidification step followed by washing the clay results in a homogenous polymer-clay film. The source of montmorillonite was found to have an effect on the morphology of the clay in the resulting composite. Montmorillonite was obtained from two sources and different clay structures within the polymer clay composites were identified in each case, indicating that the choice of clay is an important consideration when producing poly(vinyl alcohol) montmorillonite composites with higher clay content.
Li, J & Hao, H 2011, 'A Two-Step Numerical Method for Efficient Analysis of Structural Response to Blast Load', International Journal of Protective Structures, vol. 2, no. 1, pp. 103-126.
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Even with modern computer power, detailed numerical modeling and simulation of structure response to blast loads are still extremely expensive and sometimes prohibitive because it is very time consuming and requires huge computer memory. Often compromise has to be made between simulation efficiency and simulation accuracy. A lot of research efforts have been spent on improving the computational efficiency. Most of these researches concentrate on simplifying the structures, such as simplifying a structure to an equivalent SDOF system, use smeared reinforcement steel and concrete model, use substructure approach to only model part of the structure in detail. Although these approaches under certain conditions yield reliable predictions, each of them has its associated limitations. Recently a two-step method was developed to improve the computation and modeling efficiency of structure response to blast loads. Instead of simplifying the structure, the proposed method calculates the structural responses in two steps. The first step calculates the structural responses in the loading phase and the second calculates the free vibration responses with the velocity profile of the structure at the end of the loading phase as initial conditions. Using a reinforced concrete beam as the example, it was found that the proposed method yields reliable predictions of the overall beam deflection and stress in longitudinal reinforcement bars with less than 10% computational time as compared to a detailed FE model simulation. However, the predicted stress in hoop reinforcements near the beam supports is not as good. In this paper, the method is improved by also including displacement response at the end of the forced-vibration phase as the initial conditions in the free vibration analysis. The same reinforced concrete beam is used. The results show that including the displacement initial conditions in the two-step method leads to an improved prediction of the beam re...
Li, J, Dackermann, U, Xu, Y-L & Samali, B 2011, 'Damage identification in civil engineering structures utilizing PCA-compressed residual frequency response functions and neural network ensembles', STRUCTURAL CONTROL & HEALTH MONITORING, vol. 18, no. 2, pp. 207-226.
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This paper presents a non-destructive, global, vibration-based damage identification method that utilizes damage pattern changes in frequency response functions (FRFs) and artificial neural networks (ANNs) to identify defects. To extract damage features and to obtain suitable input parameters for ANNs, principal component analysis (PCA) techniques are applied. Residual FRFs, which are the differences in the FRF data from the intact and the damaged structure, are compressed to a few principal components and fed to ANNs to estimate the locations and severities of structural damage. A hierarchy of neural network ensembles is created to take advantage of individual information from sensor signals. To simulate fieldtesting conditions, white Gaussian noise is added to the numerical data and a noise sensitivity study is conducted to investigate the robustness of the developed damage detection technique to noise. Both numerical and experimental results of simply supported steel beam structures have been used to demonstrate effectiveness and reliability of the proposed method.
Lin, ZW, Li, YJ, Zhu, JG, Wang, XL, Dou, SX, Guo, YG, Lei, G, Wang, Y, Philips, M, Cortie, M, Li, YC, Choi, K-Y & Shi, X 2011, 'Visualization of vortex motion in FeAs-based BaFe1.9Ni0.1As2 single crystal by means of magneto-optical imaging', JOURNAL OF APPLIED PHYSICS, vol. 109, no. 7, pp. 0-0.
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Superconductivity has been found in newly discovered iron-based compounds. This paper studies the motion of magnetic vortices in BaFe1.9Ni 0.1As2 single crystal by means of the magneto-optical imaging technique. A series of magneto-optical images reflecting magnetic flux distribution at the crystal surface were taken when the crystal was zero-field cooled to 10 K. The behavior of the vortices, including penetration into and expulsion from the single crystal with increasing and decreasing external fields, respectively, is discussed. The motion behavior is similar to that observed in high-Tc superconducting cuprates with strong vortex pinning; however, the flux-front is irregular due to randomly distributed defects in the crystal. © 2011 American Institute of Physics.
Su, Y, Wu, C & Griffth, MC 2011, 'Modelling of the bond–slip behavior in FRP reinforced masonry', Construction and Building Materials, vol. 25, no. 1, pp. 328-334.
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Thomas, PS, Stuart, BH, McGowan, N, Guerbois, JP, Berkahn, M & Daniel, V 2011, 'A study of ochres from an Australian aboriginal bark painting using thermal methods', JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, vol. 104, no. 2, pp. 507-513.
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The potential of thermogravimetric analysis (TG) as a tool for the characterisation of ochre paint used in indigenous Australian bark paintings has been investigated. TG has been combined with differential scanning calorimetry (DSC) and mass spectrometry
Tran, T & Ha, QP 2011, 'Networked control systems with accumulative quadratic constraint', ELECTRONICS LETTERS, vol. 47, no. 2, pp. 108-+.
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Presented is a newly developed stability condition used as the stability constraint for the model predictive control of networked control systems in an imperfect data environment. The closed-loop stability is established in real time based on the evolvement of input and output correlations prescribed in the accumulative quadratic constraint. © 2011 The Institution of Engineering and Technology.
Valipour, HR & Crews, K 2011, 'Efficient finite element modelling of timber beams strengthened with bonded fibre reinforced polymers', Construction and Building Materials, vol. 25, no. 8, pp. 3291-3300.
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This paper presents development and application of a simple and efficient frame finite element (FE) able to estimate the load-carrying capacity of timber beams flexurally strengthened with externally bonded fibre reinforced polymer (FRP) strips and near-surface mounted FRP bars. The developed element is able to model collapse due to timber crushing under compression, timber fracture under tension and FRP rupture and it is developed in the framework of a flexibility-based fibre element formulation. Furthermore, a novel method based on central difference method in conjunction with composite Simpson's integration scheme along the element axis is developed to take account of shear-slip. The developed model is employed to predict the loading capacity and the applied load-mid span deflection response of timber beams strengthened with FRP and the numerically simulated responses agree well with the corresponding experimental results. The major features of this frame FE are its simplicity and efficiency compared with more complex and computationally expensive FEs which makes it a suitable tool for practical use in design-oriented parametric studies.
Walsh, KM, Choi, M, Oberg, K, Kulke, MH, Yao, JC, Wu, C, Jurkiewicz, M, Hsu, L-I, Hooshmand, SM, Hassan, M, Janson, ET, Cunningham, JL, Vosburgh, E, Sackler, RS, Lifton, RP, DeWan, AT & Hoh, J 2011, 'A pilot genome-wide association study shows genomic variants enriched in the non-tumor cells of patients with well-differentiated neuroendocrine tumors of the ileum', Endocrine Related Cancer, vol. 18, no. 1, pp. 171-180.
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Genetic studies of midgut carcinoid cancer have exclusively focused on genomic changes of the tumor cells. We investigated the role of constitutional genetic polymorphisms in predisposing individuals to ileal carcinoids. In all, 239 cases and 110 controls were collected fromthree institutions: the Uppsala University Hospital; the Dana-Farber Cancer Institute; and the MD Anderson Cancer Center, and were genotyped using microarrays assaying >300 000 single nucleotide polymorphisms. Association with rs2208059 in KIF16B approached statistical significance (Mantel-Haenszel odds ratio=2.42, P=4.16×10 -7) at a Bonferroni-corrected level (<1.62×10-7). Using two computational algorithms, four copy-number variants (CNVs) were identified in multiple cases that were absent in study controls and markedly less frequent in ∼1500 population-based controls. Of these four constitutional CNVs identified in blood-derived DNA, a 40 kb heterozygous deletion in Chr18q22.1 corresponded with a region frequently showing loss of heterozygosity (LOH) in ileal carcinoid tumor cells based on our meta-analysis of previously published cytogenetic studies (69.7% LOH, 95% confidence interval =60.0-77.9%). We analyzed the constitutional 40 kb deletion on chr18 in our study samples with a real-time quantitative PCR assay; 14/226 cases (6.19%) and 2/97 controls (2.06%) carried the CNV, although the exact boundaries of each deletion have not been determined. Given the small sample size, our findings warrant an independent cohort for a replication study. Owing to the rarity of this disease, we believe these results will provide a valuable resource for future work on this serious condition by allowing others to make efficient use of their samples in targeted studies. © 2011 Society for Endocrinology Printed in Great Britain.
Wu, C 2011, 'Special Issue on Protection of Structures against Blast Loading', Journal of Performance of Constructed Facilities, vol. 25, no. 5, pp. 358-359.
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Wu, C & Zhou, Y 2011, 'Simplified Analysis of Foam Cladding Protected Reinforced Concrete Slabs against Blast Loadings', International Journal of Protective Structures, vol. 2, no. 3, pp. 351-365.
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Protection of infrastructure against blast loading has been receiving more attention in recent years due to occasional engineering explosion accidents, e.g., chemical plant explosion, and intentional man-made explosions, e.g., rising terrorist attacks. An effective solution to mitigate blast effects on these buildings is to protect them with sacrificial foam claddings for absorption of blast energy. However, little research has been conducted to analyze the effectiveness of metallic foam protected reinforced concrete (RC) structural members under airblast loads. This paper is to develop a numerical model to analyze the mitigation of blast effects on foam cladding protected RC members with consideration of interaction of blast load, foam layer and protected structural member. This numerical model is a simplified SDOF system where the deformability of the RC flexural member is considered in the form of the supporting spring. The stiffness of the spring K is estimated from the resistance deflection function of the RC member which is derived from combined moment curvature and moment rotation models. Material testing was conducted on aluminum foam specimens to obtain the stress stain curve which was idealised as a rigid-perfectly plastic-locking model. The resistance deflection curve of the RC slab and the idealised rigid-perfectly plastic-locking model for foam specimen were incorporated into the coupled SDOF interaction model for dynamic analysis. A field blast testing on foam protected RC slab was conducted and the accuracy of the coupled SDOF interaction model was validated by experimental data from the blast testing of the foam protected RC slab.
Wu, C, DeWan, A, Hoh, J & Wang, Z 2011, 'A Comparison of Association Methods Correcting for Population Stratification in Case–Control Studies', Annals of Human Genetics, vol. 75, no. 3, pp. 418-427.
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SummaryPopulation stratification is an important issue in case–control studies of disease‐marker association. Failure to properly account for population structure can lead to spurious association or reduced power. In this article, we compare the performance of six methods correcting for population stratification in case–control association studies. These methods include genomic control (GC), EIGENSTRAT, principal component‐based logistic regression (PCA‐L), LAPSTRUCT, ROADTRIPS, and EMMAX. We also include the uncorrected Armitage test for comparison. In the simulation studies, we consider a wide range of population structure models for unrelated samples, including admixture. Our simulation results suggest that PCA‐L and LAPSTRUCT perform well over all the scenarios studied, whereas GC, ROADTRIPS, and EMMAX fail to correct for population structure at single nucleotide polymorphisms (SNPs) that show strong differentiation across ancestral populations. The Armitage test does not adjust for confounding due to stratification thus has inflated type I error. Among all correction methods, EMMAX has the greatest power, based on the population structure settings considered for samples with unrelated individuals. The three methods, EIGENSTRAT, PCA‐L, and LAPSTRUCT, are comparable, and outperform both GC and ROADTRIPS in almost all situations.
Wu, C, Huang, L & Oehlers, DJ 2011, 'Blast Testing of Aluminum Foam–Protected Reinforced Concrete Slabs', Journal of Performance of Constructed Facilities, vol. 25, no. 5, pp. 464-474.
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Wu, C, Yu, L & Zhou, Y 2011, 'Numerical Analysis of Metallic Foam Using Microstructure Model', International Journal of Protective Structures, vol. 2, no. 4, pp. 499-513.
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It has become a critical issue that the human life and civil facility have been threatened by the increasing terroristic explosive attack. The application of cellular materials is an effective and feasible measure to mitigate blast and impact loading on buildings due to their energy absorption capacity. The Finite Element code such as LSDYNA has been used to simulate the mechanical behaviours of cellular materials. However, most of numerical models regarded the cellular materials as homogeneous materials on the macro level which may affect the accuracy of simulation, because none of them can reflect the pore structure of cellular materials, especially for the irregular metallic foam structures. Therefore, in this study, two main microstructure models (2D/3D metallic foam) were developed for numerical simulation of closed-cell metal. In the microstructure model of metallic foam, the cell walls were represented by thin shell elements and the solid wall material of the cells is modelled as bi-linear stress-strain relationship based on the material properties of the cell wall material of metallic foam. The numerical models were validated through comparing simulated results with analytical values of plateau phase stress-strain response under static condition. With the validated microstructure models, a series of parametric studies were conducted, in order to have a better understanding about the mechanical properties of closed-cell metallic foam. The emphases of this study were on the differences between static and dynamic performances of closed-cell metallic foam specimens in both 2D and 3D cases, the relationship between dynamic increase factor and nominal strain rate.
Yancheng, LI, Jianchun, LI & SAMALI, B 2011, 'Dynamic Performance of a Novel Magnetorheological Pin Joint', Journal of System Design and Dynamics, vol. 5, no. 5, pp. 706-715.
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Magnetorheological fluid (MRF) has received significant attention lately and MRF based devices have been proposed for structural control applications in recent years. The unique characteristics of MR fluid lies in its abilities to reversibly, repeatedly and instantly change from a free flowing liquid to a semi-solid state when exposed to a magnetic field. The electric power required to drive the MR devices can be easily provided by a battery. Possessing such unique properties, MR fluid based devices, such as MR damper, have become promising candidates in the semi-active control for civil structure applications. However, most of the published research has focused on application of MR dampers instead of exploring other type of MR devices. In addition, MR based devices exhibit complex nonlinear hysteresis behaviour and thus making their modelling a challenging task.
In this paper, a novel MR fluid based device, namely MR pin joint, is proposed as a smart structural member in development of an intelligent civil structure that can suppress unwanted vibrations to ensure safety and serviceability of the structure. After design and fabrication, experiments have been conducted to characterise dynamic behaviours of the new device under different harmonic excitations with various input currents. Response time of the MR pin joint is compared when the MR pin joint is driven under different applied currents and moving speeds. Test data shows that the MR pin joint possesses a unique behaviour in the moment-angular velocity plot. A hyperbolic hysteresis model is proposed to model such unique behaviour. The investigation presented in the paper explores dynamic performance of MR pin joint. Finally, a parametric model is developed following the investigation on the correlation of coefficients in the proposed model with the loading conditions and applied currents.
Ahmad, A, Huang, S, Wang, JJ & Dissanayake, G 1970, 'A new state vector for range-only SLAM', 2011 Chinese Control and Decision Conference (CCDC), 2011 23rd Chinese Control and Decision Conference (CCDC), IEEE, Mianyang, Sichuan, China, pp. 3404-3409.
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This paper considers the simultaneous localization and mapping (SLAM) problem where the range-only sensor is used. Landmark initialization is a critical issue in range-only SLAM due to the lack of bearing information from the robot to the landmarks. A new state vector is proposed to be used in solving the range-only SLAM. In the new state vector, the landmark position is represented in different ways under different situations. This new representation avoids the need of multiple hypotheses on the landmark positions implemented in most of the existing range-only SLAM algorithms. Simulation and experimental results demonstrate the effectiveness of the new range-only SLAM algorithm using the new state vector within the least squares framework. © 2011 IEEE.
Aoki, Y, Samali, B, Saleh, A & Valipour Goudarzi, H 1970, 'Impact of sudden failure of cables on the dynamic performance of a cable-stayed bridge', The Austroads 8th Bridge Conferences - Sustainable Bridges: The Thread of Society - proceedings Volume II, Austroads Bridge Conference, Austroads Incorporated, Sydney, Australia, pp. 310-321.
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In cable stayed bridges corrosion and fatigue as well as extreme loadings such as earthquake, lightning strike and blast may lead to loss of cables. The vulnerability of cable stayed bridges for such cable loss scenarios has not been thoroughly investigated yet and is not considered in the current design practice. Accordingly, in this paper a primary study on vulnerability of cable stayed bridges against such extreme scenarios is undertaken. A two-dimensional Finite Element (FE) model of a cable-stayed bridge is developed in ANSYS. The mid-span of the bridge studied in this paper is 600 meter long and made of a steel box. The bridge is supported by two 140 meter tall steel towers and 56 steel cables. The bridge is analysed for two different cable loss scenarios and the global response of the structure (i.e. deformation of the bridge, bending moment at mid-span of the deck and the base of the tower, and axial force for deck and each cable) following the cable loss scenarios are studied. Further, dynamic amplification factors (DAF) for deflections and internal forces are determined by comparing the results of static analysis with the results obtained from transient dynamic analysis.
Aslani, F & Nejadi, S 1970, 'A Comparison of the Bond Characteristics in Conventional and Self-Compacting Concrete, Part I: Experimental Results', 9th International Symposium on High Performance Concrete, International Symposium on High Performance Concrete, New Zealand Concrete Society, Rotorua, New Zealand, pp. 435-442.
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Self-compacting concrete (SCC) is a very flowing material that can flow through the reinforcement and fill the formworks without any need of vibration during the concrete placement process. The material properties of SCC including bond characteristics must be well understood in order to use this type of high performance concrete in structural members broadly. This paper presents a comparison of the experimental results from the nine recent investigations on the bond strength of SCC and conventional concrete (CC). The comparison is based on the measured bond between reinforcing steel and concrete by utilizing the pullout test on the embedded bars at various heights in mock-up structural elements to assess the top-bar effect and on single bars in small prismatic specimens and conducting the beam tests. The investigated affecting parameters on bond strength are: the steel bar diameter, concrete compressive strength, types of bar (plain or deformed), embedded length of the bar, concrete type, concrete cover, curing age of concrete, casting direction of concrete and height of the embedded bar along the formwork.
Aslani, F & Nejadi, S 1970, 'A Comparison of the Bond Characteristics in Conventional and Self-Compacting Concrete, Part II: Code Provisions and Empirical Equations', 9th International Symposium on High Performance Concrete, International Symposium on High Performance Concrete, New Zealand Concrete Society, Rotorua, New Zealand, pp. 443-450.
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Self-compacting concrete (SCC) is a highly workable concrete that flows through complex structural elements under its own weight. It is cohesive enough to fill the spaces of almost any size and shape without segregation or bleeding. This makes SCC become more practical wherever concrete placing is difficult, such as in heavily-reinforced concrete members or in complicated formworks. Bond behaviour between concrete and reinforcement is a primary factor in design of reinforced concrete structures. This study presents a comparison between code provisions and empirical equations with the experimental results from the recent studies on the bond strength of SCC and conventional concrete (CC). The comparison is based on the measured bond between reinforcing steel and concrete by utilizing the pullout test on the embedded bars at various heights in mock-up structural elements to assess the top-bar effect and on single bars in small prismatic specimens; and conducting the beam tests. The investigated varying parameters on bond strength are: the steel bar diameter, concrete compressive strength, concrete type, curing age of concrete and height of the embedded bar along the formwork.
Aslani, F & Nejadi, S 1970, 'Comparison of Creep Prediction Models for Self-Compacting and Conventional Concrete', 9th International Symposium on High Performance Concrete, International Symposium on High Performance Concrete, New Zealand Concrete Society, Rotorua, New Zealand, pp. 1-10.
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Realistic prediction of concrete creep is of crucial importance for durability and long-term serviceability of concrete structures. To date, research about the behaviour of self-compacting concrete (SCC) members, especially concerning the long-term performance, is rather limited. Hence, the realistic SCC creep strain prediction is an important requirement of the design process of this type of concrete structures. SCC is quite different from conventional concrete (CC) in mixture proportions and applied materials, particularly in the presence of aggregate which is limited. This paper reviews the accuracy of the creep prediction models proposed by six international codes of practice, including: CEB-FIP 1990, ACI 209R (1992), Eurocode 2 (2001), AASHTO (2004), AASHTO (2007) and AS 3600 (2009). The predicted creep strains are compared with actual measured creep strains in 60 mixtures of SCC and 17 mixtures of CC. The affecting parameters on the creep of SCC including: the water to binder ratio, binder to aggregate ratio, sand ratio, and curing age are investigated and discussed.
Aslani, F & Nejadi, S 1970, 'Comparison of Shrinkage Prediction Models for Self-Compacting and Conventional Concrete', 9th International Symposium on High Performance Concrete, 9th International Symposium on High Performance Concrete Committee, New Zealand Concrete Society, Rotorua, New Zealand, pp. 1-10.
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One of the reasons for the use of self-compacting concrete (SCC) is to improve the long-term behaviour and durability of concrete structures. However, shrinkage of SCC may be larger than conventional concrete (CC) because SCC has higher binder content and a lower coarse aggregate volume. Therefore, accurate prediction of the shrinkage deformation is an important aspect of the long term behaviour of concrete. In this study, experimental shrinkage results for 154 mixtures of SCC and 18 mixtures of CC are compared with the shrinkage strains that are calculated using the following models: CEB-FIP 1990, ACI 209R (1992), Eurocode 2 (2001), AASHTO (2004), AASHTO (2007) and AS 3600 (2009). The influence of various parameters, such as mixture design, cement content, filler content, aggregate content, and water cement ratio (w/c) on the shrinkage of SCC are also compared and discussed.
Aslani, F & Nejadi, S 1970, 'Comparison of the Analytical Models to Determine Modulus of Elasticity of Self-Compacting Concrete and Conventional Concrete', Structural Engineers World Congress 2011, Structural Engineers World Congress, SEWC, Como, Italy, pp. 1-11.
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Self-compacting concrete (SCC) can be placed under its own weight with no vibration efforts and is cohesive enough to be handled without segregation and bleeding. Modification in the mix design may have an influence on the materialâs mechanical properties. Therefore, it is important to investigate that whether all of the assumed hypotheses for conventional concrete (CC) to design the structures are also valid for SCC construction. Indubitably, the modulus of elasticity (MOE) is one of the most important mechanical properties which influences the durability and service life of reinforced concrete. MOE represents the stress-strain relationship of concrete in the elastic range and depends on the stiffness of the cement paste and aggregate, porosity, the interfacial transition zone, size of samples, and mixture proportions. This paper reviews the accuracy of the seven models for prediction of MOE for SCC and fifteen models for CC. The predicted MOE models are compared with the actual measured experimental values in 110 mixtures of SCC and 32 mixtures of CC.
Aslani, F & Nejadi, S 1970, 'Evaluation and Comparison of Analytical Models to Determine the Bond Characteristics of Steel Fibre Reinforced Self-Compacting Concrete', 9th International Symposium on High Performance Concrete, International Symposium on High Performance Concrete, New Zealand Concrete Society, Rotorua, New Zealand, pp. 1-8.
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Steel fibre reinforced self-compacting concrete (SFRSCC) can be placed and compacted under its self weight with little or no mechanical vibration. It is at the same time cohesive enough to be casted without segregation or bleeding. Steel fibres improve many of the properties of self-compacting concrete (SCC) elements including tensile strength, ductility, toughness, energy absorption capacity, fracture toughness and cracking. Although the available research regarding the influence of steel fibres on the properties of SFRSCC is limited, this paper investigates the bond characteristics between steel fibre and SCC. This by comparison of the five analytical models including (i.e. Naaman et al. (1991a,b), Dubey (1999), Cunha (2007), Soranakom (2008) and Lee et al. (2010)) with the experimental results from the four recently conducted single fibre pull-out tests. The influence of the fibre end hook, embedded length, fibre orientation angle, on the bond characteristic between fibre and SCC are determined and discussed. The accuracy of each analytical model also has been examined.
Aslani, F & Nejadi, S 1970, 'Evaluation and Comparison of the Analytical Models to Determine Tensile Strength of Self-Compacting Concrete and Conventional Concrete', Structural Engineers World Congress 2011, Structural Engineers World Congress, SEWC, Como, Italy, pp. 1-11.
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Differences in mixture proportions and applied materials between self-compacting concrete (SCC) and conventional concrete (CC) can result in an essentially effect on the physical properties and on the mechanical properties. Therefore, it is important to investigate that whether all of the assumed hypotheses for CC to design the structures are also valid for SCC construction. The tensile strength (TS) of concrete is important to predict the initiation of cracking of concrete members when it is subjected to external loads or by shrinkage alone. For design considerations, the shear, punching, anchorage, crack control, and minimum reinforcement directly depend on the tensile strength of the concrete. Relation between tensile and compressive strength of concrete changes by various factors including, the aggregate type and particle size distribution, age of the concrete, curing process and air content. This paper reviews the accuracy of the six models for SCC and nineteen models for CC for determining the TS of concrete. The predicted results are compared with the actual measured TS of concrete from the previously conducted experimental results in 86 mixtures of SCC and 26 mixtures of CC.
Aslani, F & Nejadi, S 1970, 'Evaluation and Comparison of the Analytical Models to Predict Creep and Shrinkage Behavior of Self-Compacting Concrete', Structural Engineers World Congress 2011, Structural Engineers World Congress, SEWC, Como, Italy, pp. 1-10.
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In the structures whose long-term behavior should be monitored and controlled, creep and shrinkage effects have to be included precisely in the analysis and design procedures. Creep and shrinkage, vary with the constituent and mixtures proportions, and depend on the curing conditions and work environment as well. Self-compacting concrete (SCC) contains combinations of various components, such as aggregate, cement, superplasticizer, water-reducing agent and other ingredients which affect the properties of the SCC including creep and shrinkage of the SCC. Hence, the realistic prediction creep and shrinkage strains of SCC are an important requirement of the design process of this type of concrete structures. In this study, three proposed creep models and four shrinkage models available in the literature are compared with the measured results of 52 mixtures for creep and 165 mixtures for shrinkage of SCC. The influence of various parameters, such as mixture design, cement content, filler content, aggregate content, and water cement ratio (w/c) on the creep and shrinkage of SCC are also compared and discussed.
Aslani, F & Nejadi, S 1970, 'Evaluation of Experimental Results to Determine the Bond Characteristics of Steel Fiber Reinforced Self-Compacting Concrete', Structural Engineers World Congress 2011, Structural Engineers World Congress, SEWC, Como, Italy, pp. 1-8.
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Steel fibers can improve many of the properties of self-compacting concrete (SCC) elements including tensile resistance and crack control, ductility, toughness, energy absorption capacity, and resistance to fatigue. However, the structural behavior depends on the composite action of the concrete and steel in resisting the external loads. If steel fiber undergoes the same strain or deformation as the surrounding concrete, no slip occurs between the two materials under load and a prefect bond exists. Indubitably, prediction of accurate behavior of the composite material requires precise modeling and determining of the bond characteristics. In fiber reinforced concrete (FRC), the interface between fiber and cement paste is the weakest link of the micro-structure. Therefore, the study of the behavior of fiber-paste interface is vital for understanding the mechanism of the composite behavior. This paper presents a comparison of the experimental results from the four recent investigations on the bond characteristics of steel fiber reinforced self-compacting concrete (SFRSCC). The comparison is based on the measured bond stresses between steel fiber and SCC by utilizing a single fiber pullout test. The influences of the fiber end hook, embedded length, fiber orientation angle, concrete age, and concrete cover on the pullout test of the fibers were also investigated.
Azari, B, Fatahi, B & Khabbaz, H 1970, 'Application of Creep Ratio Concept for Estimating Post-Constriction Settlement of Deep Soft Clay Deposits', ICAGE 2011 - Proceedings of the International Conference on Advances in Geotechnical Engineering, International Conference on Advances in Geotechnical Engineering, Curtin University, Perth, Australia, pp. 127-133.
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Two main different approaches have been previously proposed to predict time dependent behaviour of soft soils. (I) end of primary consolidation is unique although creep starts simultaneously with primary consolidation (Hypothesis A); (II) As creep and primary consolidation commence at the same time and creep is a time dependant phenomenon, then end of primary consolidation cannot be unique (Hypothesis B). In Hypothesis A, soil settlement is divided into two parts: primary consolidation and secondary compression which follows by primary consolidation. In Hypothesis B, soil settlement is estimated based on elasto-viscoplastic constitutive model simulating soil creep and consolidation settlement simultaneously. In this study, details of first approach based on creep ratio ( ) concept is discussed with a worked example to be used by practicing geotechnical engineers.
Crews, KI, Buchanan, AH, Quenneville, P & Pampanin, S 1970, 'Development of High Performance Structural Timver Systems for Non Residential Buildings in New Zealand and Australia', Procedia Engineering, Structural Engineering and Construction Conference, Elsevier BV, Hong Kong, pp. 1582-1589.
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Design of structural systems for commercial and multi-residential buildings throughout most parts of the world, is currently dominated by the use of reinforced and / or prestressed concrete construction, usually supported by steel or concrete beams and frames. However, recent developments throughout the world have demonstrated the potential for timber based structural systems to be used in these types of buildings for beams and columns, roof structures and floors. The advent of engineered wood products (EWP's) such as LVL and glulam has made it possible to fabricate large section, long spanning structural members that have excellent structural properties and reliability equivalent to that of steel or concrete used in the same applications. Since 2007, significant (and related) research initiatives have been undertaken in Australia and New Zealand, investigating the performance of timber and timber hybrid systems for use in large span / medium rise commercial and industrial buildings. In 2009 a research consortium of government, industry and three Universities known as the Structural Timber Innovation Company (STIC) commenced an extensive R&D 5 year program with a total budget of $10m NZD
Far, H, Fatahi, B & Samali, B 1970, 'Effects of Dynamic Soil-Structure Interaction on Performance Level of Moment Resisting Buildings Resting on Different Types of Soil', Proceedings of the 2011 Pacific Conference on Earthquake Engineering (PCEE), Pacific Conference on Earthquake Engineering (PCEE) - 'Building an Earthquake Resilient Society', New Zealand Society for Earthquake Engineering Inc., New Zealand, pp. 1-8.
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In this study, two structural models comprising five and fifteen storey moment resisting building frames are selected in conjunction with three different soil deposits with shear wave velocity less than 600m/s. The design sections are defined after applying dynamic nonlinear time history analysis based on inelastic design procedure using elastic-perfectly plastic behaviour of structural elements. These frames are modelled and analysed employing Finite Difference approach using FLAC 2D software under two different boundary conditions namely fixed-base (no soil-structure interaction), and considering soil-structure interaction. Fully nonlinear dynamic analyses under the influence of different earthquake records are conducted and the results of inelastic behaviour of the structural models are compared. The results indicate that the inter-storey drifts of the structural models resting on soil types De and Ee (according to the Australian standard) substantially increase when soil-structure interaction is considered for the above mentioned soil types. Performance levels of the structures change from life safe to near collapse when dynamic soil-structure interaction is incorporated. Therefore, the conventional inelastic design procedure excluding SSI is no longer adequate to guarantee the structural safety for the building frames resting on soft soil deposits.
Fatahi, B & Khabbaz, H 1970, 'Enhancement of Ballasted Rail Track Performance Using Geosynthetics', Advances in Pile Foundations, Geosynthetics, Geoinvestigations, and Foundation Failure Analysis and Repairs, GeoHunan International Conference 2011, American Society of Civil Engineers, Hunan, China, pp. 222-230.
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The requirement of keeping a competitive edge against other means of transportation has increased the pressure on the railway industry to improve its efficiency and decrease the maintenance costs. In this paper, several solutions are presented to improve rail track foundations including optimum particle ballast grading and confining pressure as well as stabilising tracks overlying soft soils employing different techniques. This study specifically assesses the influence of shoulder ballast and its combination with geosynthetics to reduce the track settlement due to train load. Two dimensional plane strain finite element model is adopted to simulate the track deformation. Furthermore, the potential use of geosynthetics combined with recycled and blended ballast for reduction of rail displacement is addressed. The different location of geosynthetics in rail track substructure is examined. Rail track performance can be improved by including wider shoulder ballast with geosynthetic layer, and recycled and blended ballast reinforced with geosynthetics can be used during maintenance operation to curtail future track deformation. © 2011 ASCE.
Fatahi, B, Tabatabaiefar, HR & Samali, B 1970, 'Performance Based Assessment of Dynamic Soil-Structure Interaction Effects on Seismic Response of Building Frames', GeoRisk 2011, Georisk 2011, American Society of Civil Engineers, Atlanta, Georgia, USA, pp. 344-351.
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Soil-Structure Interaction (SSI) has progressed rapidly in the second half of 20th century stimulated mainly by requirements of the nuclear power and offshore industries to improve the seismic safety. In this study, a fifteen storey moment resisting building frame is selected in conjunction with three different soil deposits with shear wave velocity less than 600m/s. The design sections are defined after applying dynamic nonlinear time history analysis based on inelastic design procedure using elastic-perfectly plastic behaviour of structural elements. These frames are modelled and analysed employing Finite Difference approach using FLAC 2D software under two different boundary conditions, namely fixed-base (no soil-structure interaction), and considering soil-structure interaction. Fully nonlinear dynamic analyses under the influence of different earthquake records are conducted and the results of inelastic behaviour of the structural model are compared. Variations of the shear modulus ratio with the shear strain are included in the nonlinear dynamic analysis. The results indicate that the inter-storey drifts of the structural model resting on soil types De and Ee (according to the Australian standard) substantially increase when soil-structure interaction is considered for the above mentioned soil types. Performance levels of the structures change from life safe to near collapse when dynamic soil-structure interaction is incorporated. Therefore, the conventional inelastic design procedure excluding SSI is no longer adequate to guarantee the structural safety for the building frames resting on soft soil deposits. Design engineers need to address the effects of dynamic SSI precisely in their design especially for construction projects on soft soils.
Fukumoto, T, Thomas, P, Stuart, BH, Adam, G, Simon, P, Shimmon, R & Guerbois, JL 1970, 'Kinetic and mechanistic analysis of the polymerisation of dimethylol urea', Proceedings of the 3rd Joint Czech-Hungarian-Polish-Slovak Thermoanalytical Conference, Slovak Chemical Society, Stara Lesna, pp. 1-5.
Hamedanimojarrad, P, Adam, G, Ray, AS, Vessalas, K & Thomas, PS 1970, 'Development of shrinkage resistant cement-based materials using fibers', ISEC 2011 - 6th International Structural Engineering and Construction Conference: Modern Methods and Advances in Structural Engineering and Construction, International Structural Engineering and Construction Conference, Research Publishing, Zurich, Switzerland, pp. 1193-1198.
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Drying shrinkage is themajor contributor to volume changes in normal strength concrete. Several classes of shrinkage compensating admixtures are known to the concrete industry. This study deals with the literature review and categorization of different classes of shrinkage reducing fibers, especially polyethylene fibers, with the objective of introducing new types of shrinkage reducing fiber. In this investigation a special type of hydrophobic polyethylene minifibers has been used in different dosages in mortar samples. The experimental results on drying shrinkage aswellasonseveralotherpropertiesarereported.Thehydrophobicminifibersshowedremarkable improvement in shrinkage reduction even at very lowconcentrations (0.1%of cementweight).
Hamedanimojarrad, P, Ray, AS, Adam, G, Thomas, P & Vessalas, K 1970, 'Evaluation of a hybrid system of admixture and fibre for development of shrinkage resistant cement-based material', 9th International Symposium on High Performance Concrete - Design, Verification & Utilization - Proceedings (TR48), International Symposium on High Performance Concrete, New Zealand Concrete Society (NZCS), Rotorua, NZ, pp. 1-8.
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Shrinkage is a crucial feature in concrete and mortar members as it results in volume change that can lead to cracking and consequently to serviceability problems. Different additives and methods have been proposed to compensate for this problem mainly through the use of shrinkage reducing admixtures, fibres and expansive agents. In this paper, several combination systems of polyethylene micro-fibre along with an inorganic expansive agent have been studied for their influence on drying shrinkage. This special type of fibre, reported to act as shrinkage reducer, had been used in different concentrations in mortars and had been shown to have advantages and disadvantages. On the other hand, expansive agent, ammonium polyphosphate, had been shown to reduce drying shrinkage and modify most of mechanical properties. Free shrinkage strains as well as some physical properties of new mixes which contain polyphosphate and polyethylene micro-fibre are reported in this study. Several combinations were used and have been shown to have promising results in drying shrinkage, physical and mechanical properties.
Holmes, MI, Crews, KI & Ding, GK 1970, 'The influence building codes and fire regulations have on multi-storey timber construction in australia', World Sustainable Building Conference, World Sustainable Building Conference, Finish Association of Civil Engineers RIL & VTT Technical Research Centre of Finlandn, Helsinki, Finland, pp. 224-235.
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Timber is an environmentally friendly building material that is both renewable and reusable, though being combustible by nature meant historically it has been viewed in some parts of the world as an inferior structural material to steel and concrete in multi-storey construction. Buildings are responsible for a substantial amount of material and energy consumption. The environmental properties of materials aren't traditionally a design or construction priority and typically cost, performance characteristics and aesthetics have governed the choice of structural materials. This trend is beginning to change as the issues associated with climate change continue to come to the forefront and governments and industry look for ways to assuage its effects. Choosing environmentally sustainable building materials is beginning to become a client and tenant expectation and industry is starting to follow suit. Life Cycle Assessment studies have outlined when timber is used as an alternative structural material to steel and concrete the overall environmental impact of the building can be reduced.
HU, H, WANG, J & LI, Y 1970, 'INVESTIGATION ON ITS VIBRATION-REDUCTION AND SHOCK-RESISTANT PROPERTIES OF A GUN RECOIL MECHANISM BASED ON MR DAMPER', Electro-Rheological Fluids and Magneto-Rheological Suspensions, Proceedings of the 12th International Conference, WORLD SCIENTIFIC, Philadelphia, Pennsylvania, USA, pp. 214-220.
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MR damper has brought out new challenges for development of the recoil mechanisms and vibration stability control of weapons because of its good electromechanical coupling performances. At present, it has been an urgent task during automatic firing to ensure its dynamic performance and its reliability of gun recoil mechanism under continuous fastly impact. For recoil mechanisms applications, MR dampers are desired to provide optimal damping force to control the recoil dynamics, so that large peak of recoil forces can be avoided with a certain limited stroke, and the firing stillness and stability are ensured. According to its vibration and shock mechanics process of gun recoil mechanism, the measurement method of its vibration-reduction and shock-resistant properties of gun recoil mechanism based on MR damper is analyzed. The results show that a gun recoil mechanism based on MR damper is quite a good vibration-reduction and shock-resistant equipment when the vibration and shock energy dissipation by damp is considered.
Indraratna, B & Nimbalkar, S 1970, 'Implications of ballast breakage on ballasted railway track based on numerical modeling', Computer Methods for Geomechanics: Frontiers and New Applications, International Conference of the International Association for Computer Methods and Advances in Geomechanics, Melbourne, Australia, pp. 1085-1092.
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Large and frequent cyclic train loading from heavy haul and passenger trains often leads to progressive track deterioration. The excessive deformation and degradation of ballast and unacceptable differential settlement of track and/or pumping of underlying soft subgrade soils necessitate frequent and costly track maintenance. A proper understanding of load transfer mechanisms and subsequent deformations in track layers is the key element for safe and economical track design and optimum maintenance procedures. Many simplifi ed analytical and empirical design methods have been used to estimate the settlement and stress-transfer between the track layers. However, these design methods are based on the linear elastic approach, and often only give crude estimates. Given the complexities of the behaviour of the composite track system consisting of rail, sleeper, ballast, sub-ballast and subgrade subject to repeated traffi c loads in a real track environment, the current track design techniques are overly simplifi ed. The track design should also account for the deterioration of ballast due to breakage and subsequent implications on the track deformations. Considering this, an elasto-plastic constitutive model of a composite multi-layer track system is proposed. Constitutive models and material parameters adopted in this numerical model are discussed. A hardening soil model with a non-associative fl ow rule is introduced to accurately simulate the strain-hardening behaviour of ballast. The breakage of ballast observed in large scale triaxial tests is also simulated based on this model. In conjunction, numerical simulations are also performed using a two-dimensional plane-strain fi nite element analysis (PLAXIS) capturing the effects of ballast breakage and track confi ning pressure. The paper also demonstrates the advantages of the proposed elasto-plastic fi nite element simulations when compared to conventional analytical methods used by practitioners that are...
Indraratna, B, Rujikiatkamjorn, C & Nimbalkar, S 1970, 'Use of Geosynthetics in Railways Including Geocomposites and Vertical Drains', Geo-Frontiers 2011, Geo-Frontiers Congress 2011, American Society of Civil Engineers, Dallas, Texas, pp. 4733-4742.
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Australia relies heavily on rail for the transportation of bulk commodities and passenger services, and has introduced faster and heavier trains in recent years due to a growing demand. Large cyclic loading from heavy haul and passenger trains often leads to progressive deterioration of the track. The excessive deformations and degradations of the ballast layer and unacceptable differential settlement or pumping of underlying soft and compressible subgrade soils necessitate frequent costly track maintenance works. A proper understanding of load transfer mechanisms and their effects on track deformations are essential prerequisites for minimising maintenance costs. The reinforcement of the track by means of geosynthetics leads to significant reduction in the downward propagation of stresses and assures more resilient long-term performance. The geocomposite serves the functions of reinforcement, drainage and separation, thereby reducing the vertical and lateral deformations. Stabilization of soft subgrade soils by using prefabricated vertical drains (PVDs) is also essential for improving the overall stability of track and to reduce the differential settlement during the operation of trains. The effectiveness of using geocomposite geosynthetic and PVDs has been observed through field measurements and finite element analyses. These have been the first fully instrumented, comprehensive field trials carried out in Australian Railways, and it was very encouraging to see the field observations matching the numerical predictions. © ASCE 2011.
Indraratna, B, Rujikiatkamjorn, C, Vinod, JS & Nimbalkar, S 1970, 'PHYSICAL AND CHEMICAL GROUND IMPROVEMENT FOR SUSTAINABLE TRANSPORTATION INFRASTRUCTURE UNDER CYCLIC LOADS', Geotechnical Engineering for Disaster Mitigation and Rehabilitation and Highway Engineering 2011, Proceedings of the 3rd and 5th International Conference, WORLD SCIENTIFIC, Semarang, INDONESIA, pp. 140-156.
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Jenkins, D, McCarthy, LM & Baweja, D 1970, 'Optimising precast bridge girders for sustainability with the use of high performance concrete', Proceedings of the 9th International Symposium on High Performance Concrete - Design, Verification & Utilization (TR48), International Symposium on High Performance Concrete, New Zealand Concrete Society (NZCS), Rotorua, NZ, pp. 1-7.
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The standard Super-T bridge girders used in Australia were developed to provide optimum performance at a time when the maximum concrete grade covered by the bridge design code was 50 MPa. This paper examines the opportunities for improved sustainability through the use of high performance concrete, considering the use of existing standard sections, modified sections optimised for higher strength grades, and the use of techniques such as hybrid pre-tensioned and post-tensioned girders, and precast girders used in continuous structures. These alternatives are compared for impact on CO2 emissions within the context of current Australian precast and bridge construction practice. In addition, the designs of the sections are reviewed based on a series of alternative concrete mix designs covering a reference Portland cement concrete mix and a series of concretes incorporating a range of supplementary cementitious materials included at different levels of cement replacement to determine efficiencies in design and impacts on the embodied energy required to manufacture the elements.
Le, T, Fatahi, B & Khabbaz, H 1970, 'Soil Creep Mechanisms and Inducing Factors', ICAGE 2011 - Proceedings of the International Conference on Advances in Geotechnical Engineering, International Conference on Advances in Geotechnical Engineering, Curtin University, Perth, Australia, pp. 241-246.
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Soft soils have been utilised intensively for urbanisation and civil infrastructural development due to the scarcity of proper soils for construction. Soft soils themselves exhibit many engineering problems, such as large settlement which occurs in long time after construction. There are a large number of studies carried out to analyze that time dependent behaviour of soft soils, resulting in the variety of theories and models. The mechanism of creep deformation is the background to propose a model for predicting the long term settlement. However, there has been no unique explanation for the behavior of soils, leading to different theories of settlement analysis and prediction. There exist two main hypotheses for settlement calculation, Hypotheses A and B, distinguished based on different elucidation about creep mechanisms. From the existing research studies, this paper aims to discuss five mechanisms of creep including (i) the breakdown of interparticle bonds, (ii) the jumping of bonds of molecules, (iii) sliding movement among particles, (iv) the water drainage in double pore system, and (v) the structural viscosity. In this study, according to the explanation of creep mechanisms, the difference of the two hypotheses will be provided. This paper also suggests a creep mechanism based on the combinations of the explained mechanisms.
Li, Y, Li, J & Samali, B 1970, 'Design of new generation magnetorheological pins', Incorporating Sustainable Practice in Mechanics of Structures and Materials - Proceedings of the 21st Australian Conference on the Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, CRC Press/Balkema, Melbourne, Australia, pp. 807-812.
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Recently, research and development of smart materials and structures for civil engineering applications have attracted increasing attentions from researchers around theworld. Smart devices can be incorporated into civil structures as smart structural members with intelligent and controllable capacities for optimally detecting and reacting to the internal and external changes.Within the smart devices, magnetorheological (MR) based devices are one of the most promising smart devices to be considered for civil structures. This paper presents a novel design of a new-generation MR pin joint with high-torque capacity. An innovative design and analysis of MR pin with radial slots at the surface of the rotary plate is proposed. Theoretical modelling is undertaken based on the material, mechanical and magnetic analyses. Parametric analysis is conducted to optimise the shape, width and depth of the slots to best accommodate the design objectives. © 2011 Taylor & Francis Group, London.
Moshiri, F, Gerber, C & Crews, KI 1970, 'State of the art on Timber Concrete Composite floor', Concrete 2011 Building a Sustainable Future, Concrete Institute of Australia - Biennial Conference, The Concrete Institute of Australia, Perth, Australia, pp. 1-12.
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Interest in timber-concrete composite (TCC) floors has increased over the last 20-30 years. Since the 1990âs, TCC solution is seen as a viable and effective alternative to conventional reinforced concrete and/or traditional timber floors in multistorey buildings. In TCC technology, a timber beam, either solid wood, glued laminated or laminated veneer lumber (LVL), is connected to a concrete slab using a connection system that resists shear forces and impedes slip between the members of the composite section. The strength, stiffness, location and number of connectors play a crucial role for the composite action and determine the structural and serviceability performance of the floor system. This paper discusses the state of the art of TCC structures. It presents a comprehensive review of the literature about the development and structural behaviour of TCC structures. The review addresses construction aspects and shear connection concepts. It evaluates experimental tests, finite element and numerical models. It discusses the influence of concrete elements. As recommendations, the best types of shear connection for cast in-situ and prefabricated TCC floors are put forward and assessed for criteria such as strength, stiffness, ductility and ease of manufacturing. Furthermore the most relevant numerical models are introduced. These models can be used to further the experimental results in parameters such as connections, configurations, geometrical and material properties.
Nejadi, S & Aslani, F 1970, 'Evaluation and Comparison of the Compressive Stress-Strain Relationships of Self-Compacting Concrete and Conventional Concrete', CONCRETE2011, BUILDING A SUSTAINABLE FUTURE, Concrete Institute of Australia - Biennial Conference, Concrete Institute of Australia, Perth, Western Australia, pp. 1-10.
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Self-compacting concrete (SCC) is considered as a concrete which can be placed and compacted under its own weight with little or no compaction. Whereas it is while being cohesive enough to be handled without segregation or bleeding at the same time. It is used to facilitate and ensure proper filling of the complex and multipart formworks and good structural performance in the heavily reinforced structural members. Modification in the mix design of SCC may have a significant influence on the materialâs mechanical properties. Therefore, it is important to investigate that whether all of the assumed hypotheses for conventional concrete (CC) to design the structures are also valid for SCC construction. The stress-strain curve represents the deformation and strength characteristics and it is an important material behaviour of the concrete. However, due to various influencing factors and the differences between SCC and CC, the proposed curves differ. Hence, it is necessary to study the stress-strain relationship of SCC with its special material composition. This paper reviews the accuracy of the well known stress-strain relationships under uniaxial compression including: Hognestad (8), Smith and Young (9), Desayi and Krishnan (10), Saenz (11), Collins and Mitchell (12) and Mazars and Pijaudier-Cabot (13) that have been developed based on the CC experimental results and are compared with the SCC stress-strain curves experimental results for uniaxial compression available in the literature.
Nicholas, A, Crews, KI & Ariyaratne, W 1970, 'Capacity of Compression Members in RTA Timber Truss Bridges', The Austroads 8th Bridge Conferences - Sustainable Bridges: The Thread of Society - proceedings Volume II, Austroads Bridge Conference, Austroads Incorporated, Sydney, Australia, pp. 268-284.
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Since the introduction of the limit state design method for Australian bridge design in the Austroads Bridge Design Code in 1992, there has not been an associated limit states timber bridge design code. The last applicable code was the working stress design version in the 1976 NAASRA Bridge Design Specification, which invoked AS 1720:1975 SAA Timber Structures Code. The RTA is constantly under pressure to replace or significantly upgrade the remaining timber bridges on NSW roads, because they do not meet current loading standards and because of the large maintenance burden they impose. Many of these bridges employ truss designs that are of heritage significance, and are listed on the State Heritage Register. It has long been recognised that AS 1720 is particularly conservative when it is applied to the design of compression members in RTA timber truss bridges. For this reason, a research and testing program was conducted at UTS in order to develop guidelines to allow reasonable prediction of compression strength of timber members in these bridges. The four primary areas that were studied are bridge timber properties, shear capacity of spacers, creep effects and buckling modes. From this testing, new guidelines have been developed.
Parsa Pajouh, A, Fatahi, B & Khabbaz, H 1970, 'Numerical Back Analysis of Smear Zone Properties for Vertical Drain Assisted Preloading in Soft Soils', ICAGE 2011 - Proceedings of the International Conference on Advances in Geotechnical Engineering, International Conference on Advances in Geotechnical Engineering, Curtin University, Perth, Australia, pp. 561-566.
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Installation of prefabricated vertical drains (PVDs) using a mandrel causes disturbance of the clay surrounding the drain, resulting in a smear zone of reduced permeability, which adversely affects consolidation process. There are two important parameters to characterize the smear effects, namely, the smear zone diameter and the permeability ratio. In this study, FLAC finites difference software has been employed to investigate the effects of smear zone characteristics on required time for preloading. The results of a fully instrumented trial embankment in Sunshine Motorway, Queensland, have been used to verify the model, and parametric studies have been conducted on the predicted ground settlement and pore water pressure. According to the results, changes in smear zone parameters can significantly affect the consolidation period. It is observed that the characteristics of smear zone namely size and permeability have a substantial impact on the preloading design to achieve a certain soil strength and stiffness satisfying both bearing capacity and settlement design criteria.
Ren, XT, Luo, X & Wang, JJ 1970, 'Automatic road clearance surveying with sensor fusion', Proceedings of the 2011 Australasian Conference on Robotics and Automation, Australasian Conference on Robotics and Automation, The Australian Robotics and Automation Association Inc. (ARAA), Monash University, Melbourne Australia, pp. 1-8.
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This paper introduces an automatic road clearance surveying (ARCS) method based on sensor fusion. Equipped with laser measurement system (LMS), camera and proprioceptive sensors (IMU and Odometer), this system is very efficient with improved personal safety. The LMS sensors measure surroundings by collecting range and remission data. Range data is processed to build up 3D model of surveyed objectives with position and attitude information from the proprioceptive sensors. Remission data is used for extracting traffic lanes. The lowest points detected within each lane are considered to be the lanes' clearance, and marked on the 3D model. Experimental results of a vehicle mounted prototype demonstrate its performance for automatic road clearance surveying.
Saleh, A, Li, J & Lucas, J 1970, 'Internet-hosted assessment system for effective teaching and enhanced learning for engineering subjects', Proceedings of the 22nd Annual Conference for the Australasian Association for Engineering Education (AAEE2011) - Developing Engineers for Social Justice: Community Involvement, Ethics & Sustainability, AAEE - Annual Conference of Australasian Association for Engineering Education, Engineers Australia, Fremantle, WA, pp. 505-509.
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Despite of their popularity, online Learning Management Systems suffer serious limitations as a reliable and effective assessment tool in their implementation for engineering education, partly due to their demand for equation manipulation and multiple stage problem solving. An innovative spreadsheet based assessment tool (e-Task) which is designed to overcome such shortcoming and provides effective teaching and enhanced learning for engineering subjects has been proposed by the authors. The tool was developed for both formative and summative assessments with a capability to automatically collect not only results but also feedback from students on their perceived learning. Building on the previous work, this paper presents a further development by introducing a new deployment concept of the e-Task through internet-hosting of the system in order to enable effective teaching and enhanced learning of engineering subjects. The proposed internet-hosted assessment system (e-Task) integrates state-of-the-art cloud computing technology by incorporating a spreadsheet-like environment that can accommodate a wider range of users and course developers as well as enables easier expansion of the system in the future. It greatly enhances the fundamental concepts proposed in the original e-Taks by offering better accessibility, flexibility and controllability. It obviates any need of a specific software or hardware for the operational platform and requires only Internet access for its operation. Features of the Internet hosted e-Task include: the ability to access it by various Internet browsers, embedding learning and diagnostic feedback, individualised data sets for each students and automated marking & feedback.
Samali, B, Fatahi, B & Tabatabaiefar, HR 1970, 'Seismic behaviour of concrete moment resisting buildings on soft soil considering soil-structure interaction', Incorporating Sustainable Practice in Mechanics of Structures and Materials - Proceedings of the 21st Australian Conference on the Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, CRC Press/Balkema, Melbourne, Australia, pp. 407-412.
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In this study, the effects of soil-structure interaction (SSI) on the seismic behaviour of reinforced concrete moment resisting building frames are studied using finite difference method. Two types of mid-rise structures, consisting of 5 and 15 stories on soft soil, are selected and analysed. The above mentioned frames are analysed under two different boundary conditions: (i) fixed-base (no soil-structure interaction), and (ii) considering soil-structure interaction. To model soil-structure interaction, the soil medium considering soil's non-linear damping and plasticity with interface elements between soil and structure is included. The results of the analyses in terms of structural forces and lateral displacements for the above mentioned boundary conditions for different earthquakes are compared. It is observed that lateral deflections and drifts of the structures increase when SSI is included. © 2011 Taylor & Francis Group, London.
Samali, B, Li, J, Crews, K & Choi, FC 1970, 'Damage evaluation of a repaired timber beam using modal-based method', Incorporating Sustainable Practice in Mechanics of Structures and Materials - Proceedings of the 21st Australian Conference on the Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, CRC Press/Balkema, Melbourne, Australia, pp. 751-755.
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For bridge structures, global damage evaluation and structural health monitoring using modal based damage identification methods have dominated recent worldwide research. However, to date there are few works reported on the effectiveness of the methods to evaluate the new conditions after the damaged structures have been repaired. In this paper, a modal based damage identification method for localisation of damage in a timber beam, utilising modal data from before and after damage as well as after repair, is presented based on experimental results. The method employs modal parameters that monitor changes in modal strain energy of damaged and repaired beams with respect to the undamaged one. Experimental modal analysis is used in the experimental work to acquire the modal parameters required by the method. The study aims to investigate the capability and limitations of the proposed method for identifying locations of damage in damaged and repaired timber structures. © 2011 Taylor & Francis Group, London.
Shrestha, B, Khabbaz, H & Fatahi, B 1970, 'Experimental Evaluation of Seismic Deformation Characteristics of Vertical-Horizontal Reinforced Soil Walls', ICAGE 2011 - Proceedings of the International Conference on Advances in Geotechnical Engineering, International Conference on Advances in Geotechnical Engineering, Curtin University, Perth, Australia, pp. 797-802.
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Reinforced soils have been widely used in different construction applications including retaining walls. The performance of retaining walls employing vertical reinforcement in conjunction with horizontal reinforcement is investigated experimentally. This paper presents an experimental study of the seismic performance of vertical-horizontal reinforced soil wall on the simulated earthquake using reducedscale shake table tests. Construction of model retaining walls, instrumentation and results from shaking table tests are described in detail. Two types of reinforced walls, conventional horizontal reinforcement and vertical-horizontal reinforcement, were subjected to large shake of the earthquake motions. The geometry of the model, soil properties and reinforcement characteristics has been kept identical in all tests. The reinforcements used were polymeric geogrids, which were connected to the wrap-facing. Each consecutive horizontal reinforcement layers were connected in tension to each other with the help of vertical connections. The walls were instrumented using transducers to measure wall facing displacement, and accelerations within the soil. The magnitude of lateral displacement under base excitation significantly reduced when vertical reinforcement was included to the wall system.
Shrestha, B, Khabbaz, H & Fatahi, B 1970, 'PERFORMANCE ANALYSIS OF REINFORCED SOIL FOUNDATION STRUCTURES WITH VERTICAL REINFORCEMENT', GEOTECHNICAL ENGINEERING FOR DISASTER MITIGATION AND REHABILITATION 2011/GEOTECHNICAL AND HIGHWAY ENGINEERING - PRACTICAL APPLICATIONS, CHALLENGES AND OPPORTUNITIES, 3rd Int Conf on Geotechnical Engn for Disaster Mitigation and Rehabilitation/5th Int Conf on Geotechnical and Highway Engn - Practical Applications, Challenges and Opportunities, WORLD SCIENTIFIC PUBL CO PTE LTD, Semarang, INDONESIA, pp. 443-448.
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This study examines the performance of geosynthetic reinforced wall inserting vertical elements in conjunction with conventional horizontal reinforcements. In this system, similar to normal reinforcement, the selected granular material is compacted over the horizontal reinforcement up to the designed height and then another layer of horizontal reinforcement is laid down. Numerical investigations have been carried out using finite element software, PLAXIS. Geosynthetic reinforced soil foundation performance and its characteristics have been simulated with and without vertical reinforcement under static and dynamic loads. Numerical results show that the total settlement decreases by inserting inclined reinforcement in both static and dynamic loading in general, and particularly under seismic loading. A new bearing capacity formula incorporating the contribution of both vertical and horizontal reinforcements is also introduced based on the previously published studies and the outputs of this numerical simulation.
Shrestha, B, Khabbaz, H & Fatahi, B 1970, 'Performance Comparison of Vertical-Horizontal with Conventional Reinforced Soil Walls Using Numerical Modelling', PROCEEDINGS OF THE 15TH AFRICAN REGIONAL CONFERENCE ON SOIL MECHANICS AND GEOTECHNICAL ENGINEERING: RESOURCE AND INFRASTRUCTURE GEOTECHNICS IN AFRICA: PUTTING THEORY INTO PRACTICE, 15th African Regional Conference on Soil Mechanics and Geotechnical Engineering (ARCSMGE), IOS PRESS, Maputo, MOZAMBIQUE, pp. 237-242.
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Conventional reinforced soil walls have demonstrated acceptable performance during earthquake occurrences. Nevertheless, there is still some potential for enhancing the performance of these walls without increasing the cost significantly. This paper presents an overview on the application of vertical components to the reinforced soil in addition to the horizontal reinforcement. The performance of conventional and the modified reinforced soil walls are evaluated and compared to each other. In this study, a series of 2D models is carried out using PLAXTS, finite element software, to investigate behaviour of these walls. The performance of reinforced walls is evaluated under the seismic loads of Kobe earthquake. The results indicate that the proposed wall with vertical reinforcement has superior performance compared with the conventional method and can reduce the risk of failure during earthquakes.
Sofi, M, Mendis, P, Baweja, D & Elvira, E 1970, 'Bond performance of strand and wire in early age concrete', Proceedings of the 9th International Symposium on High Performance Concrete - Design, Verification & Utilization (TR48), International Symposium on High Performance Concrete, New Zealand Concrete Society (NZCS), Rotorua, NZ, pp. 1-10.
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Many failures have occurred in the live and dead end anchors of post-tensioned (PT) suspended slabs during the post-tensioning process, prompting a closer study of the behaviour of anchorage zone concrete. In suspended slabs, the post-tensioning loads are transferred to concrete mass via an anchorage assembly that consists in a strand and anchor component. As a part of wider study to establish the failure mechanism of anchorage zone concrete, pullout tests are carried out to investigate the bond behaviour of the strand and wire in early age concrete. Direct type pullout specimens were tested at 3, 4, 7, 14 and 21 days after pouring the concrete. The aim of the experiments was to evaluate the bond performance of strand and wire in high early strength concrete. Selected experimental results and a finite element model representing the pullout tests are presented in this paper. The model is validated based on the load-displacement results. Relevant parameters are discussed.
Sofi, M, Mendis, PA, Baweja, D & Elvira, E 1970, 'Anchorage zones behaviour of early age concrete: Application to post-tensioned members', Incorporating Sustainable Practice in Mechanics of Structures and Materials - Proceedings of the 21st Australian Conference on the Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, pp. 261-266.
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Anchorage zones of post-tensioned (PT) concrete slabs experience concentrated stresses as a result of post-tensioning procedures during the construction. The PT load is applied at two different stages after casting the concrete. This is to prevent shrinkage cracks and to overcome pre-stressing losses. During the early ages, however, concrete undergoes exothermic hydration reaction resulting in volume changes and associated thermal and time-dependent strains. During this time, if the strength development is lagging behind the induced stresses, severe micro-cracking can result. This can be a precursor to anchorage zone failures. To illustrate the case, Finite Element simulation of a rectangular section anchorage specimen is presented. The model consists in two distinct phases: the first phase simulates the hydration and associated thermal effects, and the second phase discusses the mechanical load imposed while the concrete hydration is ongoing. © 2011 Taylor & Francis Group, London.
Sofi, M, Zhang, L, Mendis, PA & Baweja, D 1970, 'Early age concrete creep: Using model B3 prediction', Incorporating Sustainable Practice in Mechanics of Structures and Materials - Proceedings of the 21st Australian Conference on the Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, pp. 267-272.
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Thermal and visco-elastic effects are more pronounced in early age concrete (1 to 7 days). This is due to the presence of free water and un-hydrated cementious particles. It is common practice to load the structural members during this time in order to meet the tight construction schedule. As a result, regions of high stress concentrations, such as anchorage zones in post-tensioned (PT) members, experience higher time dependent strains. This paper discusses the early age concrete effects and the predictions of early age creep strains using B3 model. A simple cylindrical specimen is considered for the analysis. © 2011 Taylor & Francis Group, London.
Tran, T & Ha, QP 1970, 'Decentralised Predictive Control with Energy Dissipation Bounds for Wireless Structural Control Applications', 28th International Symposium on Automation and Robotics in Construction (ISARC 2011), 28th International Symposium on Automation and Robotics in Construction, International Association for Automation and Robotics in Construction (IAARC), Seoul Korea, pp. 39-44.
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Decentralized control architectures for multi-storey buildings using wireless sensors and distributed embedding systems have been attracting more research recently. The designs for this application are however limited by the computational capacity embedded in each subsystem, the communication bandwidth and range of wireless channels, as well as the temporal constraints for real-time seismic protections. This paper presents a novel decentralized predictive control (DPC) strategy which can meet these design constraints. The control design takes into account the guaranteed closed-loop stability for the large-scale structure which is established from the dissipative systems theory. The proposed DPC strategy features two offline control laws to be switched-over online to minimize the computational and communication demands. By emulating the energy dissipation rate with a stabilizing constraint for the DPC optimization, the seismic protection performance of structural networked controls can be improved. The approach is designated with energy-dissipation DPC for structures using semiactive dampers. The approximated polynomial models of magneto-rheological (MR) dampers are adopted for linear systems in decentralized control designs. A numerical example is provided to illustrate the analytical developments.
Tran, T & Ha, QP 1970, 'Set-point tracking semi-automatic control of interconnected systems with input disturbances', Proceedings of the 2011 Australian Control Conference, AUCC 2011, Australian Control Conference, Engineers Australia & IEEE, Melbourne Australia, pp. 224-229.
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This paper presents the novel concept of incrementally accumulative quadratic constraint (IAQC) and its use in the constrained stabilisation for complex interconnected systems in set-point control (set-point tracking) schemes. IAQC is an incremental and discrete-time version of the integral quadratic constraint (IQC) in the time domain. A constructive method of stabilising agents for use with decentralised model predictive controllers (MPC) in semi-automatic modes is subsequently introduced. Here, the nonzero set-point control and local disturbances are effectively dealt with by employing a quadratical dissipativity criterion w.r.t control inputs and plant outputs, and a norm bounded gain for the disturbance input and plant output pair. The procedure of IAQC-based stabilising agents accommodates the coexistence of feedback control and man-in-the-loop regulation. The multiplier matrices of the IAQC are updated on-the-fly to assure the constrained feasibility. The control application of a counter-current washing circuit in a hydrometallurgical process is simulated to illustrate the viability of the presented stabilising agent. © 2011 ENGINEERS AUSTRALIA & AUSTRALIAN OPTICAL.
Tran, T, Ha, QP & Nguyen, HT 1970, 'Semi-automatic control of modular systems with intermittent data losses', 2011 IEEE International Conference on Automation Science and Engineering, 2011 IEEE International Conference on Automation Science and Engineering (CASE 2011), IEEE, Trieste Italy, pp. 625-630.
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This paper presents a control procedure of distributed stabilising agents for dynamically-coupled systems operating in the imperfect data environment of a mesh device network. A multivariable controller is applied to each single modular subsystem, which also allows for a manual control mode. To deal with the device network, intermittent data losses are compensated for on-the-fly using the incrementally accumulative quadratic constraint (AQC). The incrementally AQC is employed in the procedure of stabilising agents to accommodate the coexistence of closed-loop control and man-in-the-loop regulation. These agents render stabilising bounds for the manipulated variables in the automatic control mode, and at the same time, provide warning signals and manipulation guidance for the operators to prevent possible plant-wide destabilisation in the semi-automatic control mode. Taking the control constraints into consideration, the feasibility of AQC-based stabilising bounds is guaranteed for the consecutive datalost periods of device networks. The innovative aspect of the proposed approach rests on the stability condition developed from the input and output evolution prescribed in the controller AQC and the system dissipativity, as well as the method of remedying data losses right after the incidents. Simulation results are provided for the model predictive control of an industrial modular system in the mineral processing industry. © 2011 IEEE.
Tran, T, Ha, QP, Nguyen, HT & Tuan, HD 1970, 'Toward Plant-wide Control of Reticulated Systems Arising in Alumina Refineries with Online Stabilisation', IFAC Proceedings Volumes, IFAC World Congress, Elsevier BV, Milano Italy, pp. 10529-10534.
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This paper presents a novel distributed model predictive control strategy for reticulated systems of the alumina refining process. The plant-wide control is facilitated by the constructive method of online stabilisations that is applicable to the model predictive controllers (MPC) as stability constraints. The plant-wide process is modeled as a large-scale system formed by the subsystems of different unit operations interconnected to each other. The stability condition for the interconnected system is derived from the accumulative quadratic constraint (AQC), which is subsequently developed into receding-horizon stability constraints for MPC. The proposed online stabilisation scheme can be implemented for a department and/or the whole alumina refinery, which consists of four main departments of digestion, clarification, precipitation-filtration, and evaporation. The theoretical results are illustrated by simulations for a typical example of three dynamically-coupled subsystems.
Wu, C & Yu, L 1970, 'Simulation of cellular materials using micro-scale model', Proceedings of the 9th International Conference on Shock and Impact Loads on Structures, International Conference on Shock and Impact Loads on Structures, Fukuoka, Japan, pp. 669-676.
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Cellular material is a typical micro-scale crushable material due to its special pore microstructures. The mechanical properties of a cellular material are usually determined from experimental testing and based on stress-strain curves for normal and shear loading. Since such tests are associated with a large amount of time and cost with regard to specimen preparation and test devices, an alternative way of determining the effective mechanical properties can be investigated using micro-scale modelling that is through virtual material testing. In this paper a finite element program LSDYNA is used to develop a micro-scale model for a cellular material honeycomb. In the micro-scale model of honeycomb, the cell walls are represented by thin shell elements and the solid wall material of the cells is modelled as bi-linear stress-strain relationship based on the material properties of the cellular materials. The developed micro-scale model is validated through comparing the simulated results with the experimental information. The validated micro-scale model is then used to simulate the material responses under the static conditions. With the micro-scale structure model, the impact response such as progressive crushing of the honeycomb and layer by layer cell collapse can be also simulated, and consequently the dynamic material properties of honeycomb can be derived such as the plateau stress enhancement increase in the energy absorption capacity of honeycomb under different loading rates.
Yang, L, Thomas, P & Stuart, BH 1970, 'DSC characterisation of thermally treated low density polyethylenes in a forensic context', Proceedings of the 3rd Joint Czech-Hungarian-Polish-Slovak Thermoanalytical Conference, Slovak Chemical Society, Stara Lesna, pp. 1-5.
