Infrastructure Engineering - Research Publications
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ItemConstructing a novel nano-TiO2/Epoxy resin composite and its application in alkali-activated slag/fly ash pastes(Elsevier, 2020-01-30)A novel in-situ synthetic method is developed for fabrication of inorganic-organic hybrid structured TiO2/Epoxy resin composite without adding any surfactants. It is discovered for the first time that the inorganic-organic micro-structured TiO2/Epoxy composite can be homogeneously dispersed in one type of alkali-activated binders: alkali-activated slag/fly ash (AASF) pastes with slag/fly ash at 50/50. Besides, it is found that TiO2/Epoxy composite is capable of enhancing the mechanical properties including compressive and flexural bending strengths, improving porous structures and reducing drying shrinkage of the AASF paste. Moreover, scanning electron microscopy results showed that the AASF binder enhanced by TiO2/Epoxy resin composite has a smooth and flat morphology with fewer cracks as compared to the control paste, leading to a denser microstructure. It is assumed that both TiO2 and epoxy resin are beneficial in improving the microstructure and hence the macroscopic properties of AASF binders were also improved. Since the preparation of TiO2/Epoxy composite through in-situ polymerization method is attractive because of its simple manufacturing procedure and cost-effectiveness, its modified AASF binders have an appealing potential to be used for large-scale production and field applications in the foreseeable future.
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ItemDetecting structural damage to bridge girders using radar interferometry and computational modelling(JOHN WILEY & SONS LTD, 2017-10)The process for assessing the condition of a bridge involves continuously monitoring changes to the material properties, support conditions, and system connectivity throughout its life cycle. It is known that the structural integrity of bridges can be monitored by measuring their vibration responses. However, the relationship between frequency changes and structural damage is still not fully understood. This study presents a bridge condition assessment framework which integrates computational modelling and noncontact radar sensor techniques (i.e., IBIS-S) to predict changes in the natural frequencies of a bridge girder as a result of a range of parameters that govern its structural performance (e.g., elastomeric bearing stiffness, concrete compressive stiffness, and crack propagation). Using a prestressed concrete bridge in Australia as a case study, the research outcomes suggest that vibration monitoring using IBIS-S is an efficient way for detecting the degradation of elastomeric bearing stiffness and shear crack propagation in the support areas that can significantly affect the overall structural integrity of a bridge structure. However, frequency measurements have limited capability for detecting the decrease in the material properties of a bridge girder.
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ItemBone fracture healing under Ilizarov fixator: Influence of fixator configuration, fracture geometry, and loading(WILEY, 2019-06-01)This study aims to enhance the understanding of the relationship between Ilizarov fixator configuration and its effects on bone fracture healing. Using Taylor spatial frame (TSF) as an example, the roles of critical parameters (ie, TSF ring diameter, wire pre‐tension, fracture gap size, and axial load) that govern fracture healing during the early stages were investigated by using computational modelling in conjunction with mechanical testing involving an advanced 3D optical measurement system. The computational model was first validated using the mechanical test results and then used to simulate mesenchymal stem cell (MSC) differentiations within different regions of the fracture site under various combinations of TSF ring diameter, wire pre‐tension, fracture gap size, and axial load values. Predicted spatially dependent MSC differentiation patterns and the influence of each parameter on differentiations were compared with in vivo results, and good agreement was seen between the two. Gap size was identified as the most influential parameter in MSC differentiation, and the influence of axial loading and TSF configuration (ie, ring diameter and wire pre‐tension) on cell differentiation was seen to be gap size dependent. Most changes in cell differentiation were predicted in the external callus (periosteal), which is the crucial region of the callus in the early stages. However, for small gap sizes (eg, 1 mm), significant changes were predicted in the endosteal callus as well. The study exhibits the potential of computational models in assessing the performance of Ilizarov fixators as well as assisting surgeons in patient‐specific clinical treatment planning.
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ItemA probabilistic study of ground motion simulation for Bangkok soil(SPRINGER, 2017-05)Due to the soft soil condition, it has been found that buildings in Bangkok locating 200 km away from epicentral of an earthquake can be damaged as a result of high ground motion (e.g. earthquakes of magnitudes 5.3–5.9 in 1983). Because of rapid urban expansion and population growth in cities with soft soil condition, such as Bangkok, the assessment of seismic vulnerability of building structures becomes necessary. The purpose of this study is to quantify variability and develop attenuation and amplification models of ground motions for Bangkok sites. First, by analysing soil profile of Bangkok using Latin Hypercube sampling technique, critical attenuation and amplification characteristics, such as peak ground acceleration, ground motion intensity, frequency content and significant ground duration, were obtained. Then, the statistical information on the attenuation and amplification models of these characteristics was established and used to conduct a series of non-linear seismic analysis of a typical four storey commercial building in Bangkok. The research outcomes demonstrate that the developed models are capable of predicting the damage indices of buildings in Bangkok under different earthquake intensities and epicentral distances.
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ItemProbabilistic modelling of forces of hail(SPRINGER, 2018-03)
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ItemRole of Dynamic Loading on Early Stage of Bone Fracture Healing(SPRINGER, 2018-11)After fracture, mesenchymal stem cells (MSCs) and growth factors migrate into the fracture callus to exert their biological actions. Previous studies have indicated that dynamic loading induced tissue deformation and interstitial fluid flow could produce a biomechanical environment which significantly affects the healing outcomes. However, the fundamental relationship between the various loading regimes and different healing outcomes has not still been fully understood. In this study, we present an integrated computational model to investigate the effect of dynamic loading on early stage of bone fracture healing. The model takes into account cell and growth factor transport under dynamic loading, and mechanical stimuli mediated MSC differentiation and tissue production. The developed model was firstly validated by the available experimental data, and then implemented to identify the loading regimes that produce the optimal healing outcomes. Our results demonstrated that dynamic loading enhances MSC and growth factor transport in a spatially dependent manner. For example, compared to free diffusion, dynamic loading could significantly increase MSCs concentration in endosteal zone; and chondrogenic growth factors in both cortical and periosteal zones in callus. Furthermore, there could be an optimal dynamic loading regime (e.g. 10% strain at 1 Hz) which could potentially significant enhance endochondral ossification.
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ItemApplication of FRP Bolts in Monitoring the Internal Force of the Rocks Surrounding a Mine-Shield Tunnel(MDPI, 2018-09)Monitoring the internal force of the rocks surrounding a mine-shield tunnel for the initial support of a mine-shield tunnel, in complex geological and hydrological environments, requires bolts with specific features such as high tensile strength, low shear strength, good insulation and resistance to corrosion. As such, internal force monitoring has become an important issue in safety monitoring for such tunneling projects. In this paper, the adaptability of a mine-shield tunnel project in a corrosive environment is investigated. A fiberglass reinforced plastic (FRP) bolt with high tensile strength, low shear strength, resistance to fatigue, non-conductivity and resistance to corrosion is used as a probe in tandem with an anchor-head dynamometer to monitor the internal force of the rocks surrounding a mine-shield tunnel for initial support. Additionally, solar energy collection technology is introduced to create a remote monitoring system. Using a 2.5 km long railway tunnel located in the northeast of the Pearl River Delta of China as a case study, the present study shows that, compared with a conventional steel bolt, the FRP bolt has advantages, such as avoidance of the risks associated with the shield machine, insulation and resistance to corrosion. As a probe, the response of the FRP bolt to events such as a blasting vibration and a construction disturbance that results in internal changes in the surrounding rock demonstrates a clear pattern that is appropriate for monitoring the internal force of the rocks surrounding a mine-shield tunnel in a corrosive environment. FRP bolt-based monitoring not only provides new technological support for controlling the risk involved in the initial support of a mine-shield tunnel but can also be widely deployed in projects with special requirements for disassembly, conductivity and corrosion.
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ItemSensitivity Analysis of Geometrical Parameters on the Aerodynamic Performance of Closed-Box Girder Bridges(MDPI, 2018-07)In this study, the influence of two critical geometrical parameters (i.e., angles of wind fairing, α; and lower inclined web, β) in the aerodynamic performance of closed-box girder bridges was systematically investigated through conducting a theoretical analysis and wind tunnel testing using laser displacement sensors. The results show that, for a particular inclined web angle β, a closed-box girder with a sharper wind fairing angle of α = 50° has better flutter and vortex-induced vibration (VIV) performance than that with α = 60°, while an inclined web angle of β = 14° produces the best VIV performance. In addition, the results from particle image velocimetry (PIV) tests indicate that a wind fairing angle of α = 50° produces a better flutter performance by inducing a single vortex structure and a balanced distribution of the strength of vorticity in both upper and lower parts of the wake region. Furthermore, two-dimensional three-degrees-of-freedom (2D-3DOF) analysis results demonstrate that the absolute values of Part A (with a reference of flutter derivative A₂*) and Part D (with a reference of A₁*H₃*) generally decrease with the increase of β, while the change of the participation level of heaving degrees of freedom (DOF) in torsion-dominated coupled flutter initially increases, reaches its peak, and then decreases with the increase of β.
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ItemReliability-Based Decision Support Framework for Major Changes to Social Infrastructure PPP Contracts(MDPI AG, 2020)In the operational phase of public-private partnership (PPP) contracts, undue delay in addressing real needs may lead to poor service outcomes; conversely, commencing variations to a PPP agreement on the whim of end-user runs the risk of reducing the value created by detailed structuring and considerations undertaken in establishing agreement. This difficulty is exasperated as there is generally a lack of understanding by the end-user as to the specifics of service delivery performance requirements contracted. In order to address this question, this study, for the first time, develops a reliability-based decision support framework (RDSF) that incorporates end-user’s perceived service quality (i.e., how satisfied it is with the space, operation and maintenance activities) with those specified in the PPP agreement, and further identifies when the gap between end-user’s expectations and contractual obligations warrants reconsideration. This developed framework is then implemented to test the data gathered from three PPP schools in Australia based on both a current snapshot of performance data, i.e., abatements as gathered through contract documents and end-user’s perception through in-depth interviews, and a projected scenario of the future as well. Reliability analysis used here compares time-dependent risk profiles of current and expected performance and thereby identifies major changes in a PPP contract that would sensibly require reconsideration. The specific results indicate there is no current difficulty between end-user’s perception and the contract. However, the projected long-term scenario demonstrates how the decision framework can identify areas for review and changes if end-users are more dissatisfied with the service being achieved. The RDSF is capable of quantifying current service performance, considering the engagement of the end-user. Thus it enriches theories in the field of performance management system (PMS), and also contributes to knowledge regarding an evidence-based test for justifying possible agreement modifications or additional works in social PPPs operations. In addition, guidance for performance improvement strategies in aspects of the dissatisfied area is also provided. Application of this approach would assist in maintaining the long-term value for money of social infrastructure PPP agreements.
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ItemAerodynamic Countermeasure Schemes of Super Long-Span Suspension Bridges with Various Aspect Ratios(WORLD SCIENTIFIC PUBL CO PTE LTD, 2020-05-01)The purpose of this study is to investigate the flutter control scheme of super long-span bridges with various aspect ratios (e.g. width to height (B/H)) using passive aerodynamic countermeasures. Through a series of wind tunnel testing and theoretical analysis, three types of passive aerodynamic countermeasures, i.e. vertical central stabilizer (VCS), wind barrier and inspection rail, were investigated for five typical aspect ratios of a closed-box girder bridge. The results show that both the aspect ratio and flutter critical wind speed generally increase with the decrease of the ratio of torsional and vertical frequencies of the bridge. In the case of an aspect ratio of 8.9, a downward VCS (DVCS) has a much better flutter performance than that of an upward VCS (UVCS) because aerodynamic damping of Part A and Part D could produce a higher heaving degree of freedom (DOF) participation level. Furthermore, the position variation of wind barriers is superior to their shape variation for the bridge with an aspect ratio of 8.3, and the flutter performance of the girder with a combination of the wind barrier (WB3P3) and UDVCS with 0.3h/H DVCS appears to be better than that without countermeasures. In addition, the installation of an inspection rail near the bottom point of an inclined-web (IR3) has the best flutter control effect among four positions of inspection rails.