Infrastructure Engineering - Research Publications
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ItemStructural Health Monitoring of Bridges Using Advanced Non-destructive Testing Technique(Springer, Singapore, 2020-01-01)This paper presents an integrated framework for structural health monitoring of bridges by using advanced non-destructive testing (NDT) technique in conjunction with computational modelling. First, the structural characteristics of the Eltham Trestle Bridge under train loading were monitored using the combination of the 3D optical measurement system and IBIS-S. The results demonstrate that, in conjunction with computational modelling, the NDT can capture the structural health conditions of the bridge by analysing the natural frequencies and deformation profiles of the critical members of the bridges. Then, the developed framework also takes into account the impact of extreme events (e.g. truck impacts and earthquakes) by using a reliability-based model. Finally, using the Montague Street Bridge as a case study, it shows that proposed framework has the capability of predicting the residual life of a bridge subject to both progressive deterioration and extreme events throughout its service life.
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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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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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ItemInfrared Thermography for Detecting Subsurface Defects of Concrete Structures(Springer Singapore, 2020-12-23)Delamination is one of the serious types of deterioration in reinforced concrete structures. It could cause concrete spalling, exposed steel bars, and ultimately affects the structural integrity of concrete structures. Infrared thermography (IRT) is a non-destructive technique which could potentially detect the delamination by capturing thermal contrast (∆T) on concrete surface caused by the heat flow disruption within the concrete due to subsurface anomalies. However, the optimum time and environmental conditions for IRT data collection are still unclear. In this study, an experimentally validated numerical model was developed to investigate the effect of a range of environmental conditions and defect characteristics on the IRT inspection outcomes. The results show that, under direct solar irradiation, the total heat flux input plays an important role in the development of thermal contrast ∆T instead of flux rate. Furthermore, delamination depth and size are two critical parameters that affect IRT results.
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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.
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ItemAerodynamic performance evaluation of different cable-stayed bridges with composite decks(Techno-press, 2020-03-10)The aerodynamic performance of long-span cable-stayed bridges is much dependent on its geometrical configuration and countermeasure strategies. In present study, the aerodynamic performance of three composite cable-stayed bridges with different tower configurations and passive aerodynamic countermeasure strategies is systematically investigated by conducting a series of wind tunnel tests in conjunction with theoretical analysis. The structural characteristics of three composite bridges were firstly introduced, and then their stationary aerodynamic performance and wind-vibration performance (i.e., flutter performance, VIV performance and buffeting responses) were analyzed, respectively. The results show that the bridge with three symmetric towers (i.e., Bridge I) has the lowest natural frequencies among the three bridges, while the bridge with two symmetric towers (i.e., Bridge II) has the highest natural frequencies. Furthermore, the Bridge II has better stationary aerodynamic performance compared to two other bridges due to its relatively large drag force and lift moment coefficients, and the improvement in stationary aerodynamic performance resulting from the application of different countermeasures is limited. In contrast, it demonstrates that the application of both downward vertical central stabilizers (UDVCS) and horizontal guide plates (HGP) could potentially significantly improve the flutter and vortex-induced vibration (VIV) performance of the bridge with two asymmetric towers (i.e., Bridge III), while the combination of vertical interquartile stabilizers (VIS) and airflow-depressing boards (ADB) has the capacity of improving the VIV performance of Bridge II.
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ItemSensitivity analysis of geometrical design parameters on the compressive strength of the vertical inner-plate reinforced square hollow section T-joints: A finite element study(Elsevier BV, 2020-04)In present study, the normalized axial compressive strength (Qu) of the vertical inner-plate reinforced (VIPR) square hollow section (SHS) T-joints was systematically investigated under various geometrical design parameters of the joint, such as width ratio of the brace and the chord (β), thickness ratio of the vertical inner plate and chord flange (τip), ratio of the outstretch length of the vertical inner plate from the brace to the width of the chord (γip), height and width ratio of the brace (η1). First, a finite element (FE) model of the VIPR SHS T-joint was developed and validated by using experimental data. Then, a large scale of parametric studies was carried out to identify the critical geometrical design parameters that influence the Qu of the VIPR SHS T-joint. The results show that Qu increases with the increase of β, and the rate of increase becomes more obvious under a large β. In addition, under a relatively small β (i.e. β < 0.6), the yielding of the chord flange is mainly controlled by the vertical inner plate, whereas the yielding of the chord flange is controlled by the brace under a large β. It also demonstrates that the vertical inner plate can mitigate the risk of buckling failure of chord web, and Qu increases with the increase of γip. Furthermore, this study proposed an empirical equation which could potentially be used by the practicing engineers to evaluate the axial compressive strength of VIPR SHS T-joints under various geometrical design parameters.
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ItemComputational study on synovial fluid flow behaviour in cartilage contact gap under osteoarthritic condition(Elsevier, 2020-08-01)This study numerically investigates the pathological changes of fluid flow in cartilage contact gap due to the changes in cartilage surface roughness and synovial fluid characteristics in osteoarthritic (OA) condition. First, cartilage surface topographies in both healthy and OA conditions are constructed using a numerical approach with consideration of both vertical and horizontal roughness. Then, constitutive equations for synovial fluid viscosity are obtained through calibration against previous experimental data. Finally, the roughness and synovial fluid information are input into the gap flow model to predict the gap permeability. The results show that the rougher surface of OA cartilage tends to decrease gap permeability by around 30%–60%. More importantly, with the reduction in gap size, the decrease in gap permeability becomes more significant, which could result in an early fluid ultrafiltration into the tissue. Moreover, it is demonstrated that the pathological synovial fluid has more deleterious effects on the gap permeability than the OA cartilage surface, as it could potentially increase the gap permeability by a few hundred times for pressure gradients less than 106 Pa/m, which could inhibit the fluid ultrafiltration into the tissue. The outcomes from this research indicate that the change in fluid flow behaviour in contact gap in OA condition could significantly affect the function of articular joints.
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ItemInfluence of aggregate surface treatment on corrosion resistance of cement composite under chloride attack(Elsevier BV, 2020-07-10)The high porosity of interfacial transition zone (ITZ) could significantly influence the durability of offshore concrete structures. This study aims to investigate the effects of aggregate surface by coating slag and silica fume on the ITZ microstructure, ultimately the corrosion resistance of the cement composite materials exposed to chloride attack. First, a series of experimental studies on chloride transport were carried out. Then, an experimentally validated model was developed to further understand the fundamental reactive-transport behaviour of chlorides in concrete in relation to different aggregate surface coating methods. The experimental results show that aggregate surface coating using silica fume can significantly reduce the porosity of interfacial transition zone (e.g. more than 40% reduction of porosity 5 μm from aggregate surface). Most importantly, the numerical predictions indicate that the slag and silica fume coating could potentially prolong the initiation time of the steel bar corrosion in offshore structures by more than 60% and 170%, respectively.