Infrastructure Engineering - Research Publications
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ItemA Simplified Methodology for Condition Assessment of Bridge Bearings Using Vibration Based Structural Health Monitoring Techniques(WORLD SCIENTIFIC PUBL CO PTE LTD, 2021-09-01)The mechanical properties of bridge bearings gradually deteriorate over time resulting from daily traffic loading and harsh environmental conditions. However, structural health monitoring of in-service bridge bearings is rather challenging. This study presents a bridge bearing condition assessment framework which integrates the vibration data from a non-contact interferometric radar (i.e. IBIS-S) and a simplified analytical model. Using two existing concrete bridges in Australia as a case study, it demonstrates that the developed framework has the capability of detecting the structural condition of the bridge bearings in real-time. In addition, the results from a series of parametric studies show that the effectiveness of the developed framework is largely determined by the stiffness ratio between bridge bearing and girder ([Formula: see text], i.e. the structural condition of the bearings can only be effectively captured when the value of [Formula: see text] ranges from 1/100 and 100.
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ItemLife-cycle modelling of concrete cracking and reinforcement corrosion in concrete bridges: A case study(Elsevier BV, 2021-06-15)The development of effective life cycle management strategies for transport infrastructure assets is of importance for meeting the defined public policies and levels of service. In the last decades, much progress has been made in assessing the life-cycle performance of bridges using reliability-based approaches. However, the goal of developing a comprehensive life-cycle performance assessment framework for bridges has not been fully achieved. This is due to the uncertainties surrounding model parameters as well as the correlation between these parameters (e.g. the complex correlation between the reinforcement corrosion and the concrete cracking). It becomes more challenging due to the limited access to bridge inspection data by bridge research communities resulting from confidentiality issues. Using a typical highway concrete bridge as a case study, the present study systematically investigated the impact of concrete crack induced reinforcement corrosion on the serviceability of concrete bridges by developing an engineering reliability-based approach involving an auto-regressive crack propagation model and a steel corrosion prediction model. The model parameters were calibrated using the eight-year inspection data of an operating bridge. The influence of different external environments in the reinforcement corrosion, ultimately the residual life of the bridges, was also investigated through conducting a series of parametric studies. Based on the collected bridge inspection data, the model results predict that, although the surface crack of a RC bridge is repairable through periodic maintenance, the corrosion of the steel bars in the bridge still continues over time with a corrosion rate which depends on different maintenance intervention cycle periods (Tcycle). For example, reducing Tcycle from 12 years to 4 years could potentially prolong the service life of the bridge by around 15 years. The developed model could assist bridge managers to estimate the optimal Tcycle to prolong the service life of bridges.
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ItemThe investigation of bone fracture healing under intramembranous and endochondral ossification(ELSEVIER, 2021-06)After trauma, fractured bone starts healing directly through bone union or indirectly through callus formation process. Intramembranous and endochondral ossification are two commonly known mechanisms of indirect healing. The present study investigated the bone fracture healing under intramembranous and endochondral ossification by developing theoretical models in conjunction with performing a series of animal experiments. Using experimentally determined mean bone densities in sheep tibia stabilized by the Locking Compression Plate (LCP) fixation system, the research outcomes showed that intramembranous and endochondral ossification can be described by Hill Function with two unique sets of function parameters in mechanical stimuli mediated fracture healing. Two different thresholds exist within the range of mechanical simulation index which could trigger significant intramembranous and endochondral ossification, with a relatively higher bone formation rate of endochondral ossification than that of intramembranous ossification. Furthermore, the increase of flexibility of the LCP system and the use of titanium LCP could potentially promote uniform bone formation across the fracture gap, ultimately better healing outcomes.
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ItemInvestigation of role of cartilage surface polymer brush border in lubrication of biological joints(Springer Science and Business Media LLC, 2021)Although experimental evidence has suggested that the polymer brush border (PBB) on the cartilage surface is important in regulating fluid permeability in the contact gap, the current theoretical understanding of joint lubrication is still limited. To address this research gap, a multiscale cartilage contact model that includes PBB, in particular its effect on the fluid permeability of the contact gap, is developed in this study. Microscale modeling is employed to estimate the permeability of the contact gap. This permeability is classified into two categories: For a gap size > 1 µm, the flow resistance is assumed to be dominated by the cartilage roughness; for gap size < 1 µm, flow resistance is assumed to be dominated by the surface polymers extending beyond the collagen network of the articular cartilage. For gap sizes of less than 1 µm, the gap permeability decreases exponentially with increasing aggrecan concentration, whereas the aggrecan concentration varies inversely with the gap size. Subsequently, the gap permeability is employed in a macroscale cartilage contact model, in which both the contact gap space and articular cartilage are modeled as two interacting poroelastic systems. The fluid exchange between these two media is achieved by imposing pressure and normal flux continuity boundary conditions. The model results suggest that PBB can substantially enhance cartilage lubrication by increasing the gap fluid load support (e.g., by 26 times after a 20-min indentation compared with the test model without a PBB). Additionally, the fluid flow resistance of PBB sustains the cartilage interstitial fluid pressure for a relatively long period, and hence reduces the vertical deformation of the tissue. Furthermore, it can be inferred that a reduction in the PBB thickness impairs cartilage lubrication ability.
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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.
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ItemThe influence of ambient environmental conditions in detecting bridge concrete deck delamination using infrared thermography (IRT)(Wiley, 2020-04-01)Delamination is a serious form of deterioration in concrete bridge decks. Infrared thermography (IRT) is an advance non‐destructive testing method for concrete bridge deck delamination detection by capturing the absolute thermal contrast (ΔT) on the concrete surface caused by the disruption in heat flow due to subsurface defects. However, as the ambient environmental conditions (e.g. wind velocity and solar radiation) of a bridge could significantly affect the measurement outcomes of IRT, the optimal times for infrared data collection are still unclear. In this paper, a series of experimental and numerical studies were carried out to investigate the effects of the rate of heat flux and wind velocity on ΔT on the surface of bridge decks with the aim of identifying the optimal inspection times for different geometry characteristics of delamination (i.e. size and depth). The developed model is firstly validated by the experimental data and then a series of parametric studies were carried out. The result shows that the heat flux rate plays an important role in the development of ΔT on concrete surface, especially for a relatively shallow and small size delamination. However, the influence of heat flux rate gradually diminishes with the increase in size and depth of delamination. In addition, it demonstrates that there is a positive linear correlation between the total heat energy (external irradiation) and square of the delamination depth. The current research represents an important step towards the development of an effective and efficient way for defect detection using IRT.
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ItemA coupled contact model of cartilage lubrication in the mixed-mode regime under static compression(Elsevier, 2020-05-01)This study presents a coupled cartilage contact model, in which the contact gap and cartilage tissue are modelled as two poroelastic systems, linked by pressure and normal flux continuity boundary conditions. Using a tibial plug under indentation as a proof-of-concept model, the predictions support the weeping lubrication theory under static compression. Specifically, the interstitial fluid would exude from the underlying cartilage into the contact gap to extend the mixed-mode duration by > 20-fold compared to a no fluid exudation counterpart. Moreover, the traditional contact model, that does not consider the contact gap and cartilage fluid exchange, potentially overestimates the interstitial fluid pressure compared to the proposed coupled model. Parametric studies suggest that the increasing viscosity of synovial fluid prolongs the gap fluid pressurisation, while increasing the asperity stiffness reduces the gap fluid pressure but increases contact gap height.
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ItemA probabilistic approach for modelling bone fracture healing under Ilizarov circular fixator(WILEY, 2021-07)Bone fracture treatments using Ilizarov circular fixator (ICF) involve dealing with uncertainties about a range of critical factors that control the mechanical microenvironment of the fracture site such as ICF configuration, fracture gap size, physiological loading etc. To date, the effects of the uncertainties about these critical factors on the mechanical microenvironment of the fracture site have not been fully understood. The purpose of this study is to tackle this challenge by using computational modelling in conjunction with engineering reliability analysis. Particularly, the effects of uncertainties in fracture gap size (GS), level of weight-bearing (P), ICF wire pretension (T) and wire diameter (WD) on the fracture site mechanical microenvironment at the beginning of the reparative phase of healing was investigated in this study. The results show that the mechanical microenvironment of fracture site stabilised with ICF is very sensitive to the uncertainties in P and GS. For example, an increase in the coefficient of variation of P (COVP ) from 0.1 to 0.9 (i.e., an increase in the uncertainty in P) could reduce the probability of achieving a favourable mechanical microenvironment within the fracture site (i.e., Probability of Success, PoS) by more than 50%, while an increase in the coefficient of variation of GS (COVGS ) from 0.1 to 0.9 could decrease PoS by around 30%. In contrast, an increase in the uncertainties in T and WD (COV increase from 0.1 to 0.9) has little influence on the fracture site mechanical microenvironment (PoS changes <5%).
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ItemThe status and challenges of replicating the mechanical properties of connective tissues using additive manufacturing(Elsevier BV, 2020-03)The ability to fabricate complex structures via precise and heterogeneous deposition of biomaterials makes additive manufacturing (AM) a leading technology in the creation of implants and tissue engineered scaffolds. Connective tissues (CTs) remain attractive targets for manufacturing due to their “simple” tissue compositions that, in theory, are replicable through choice of biomaterial(s) and implant microarchitecture. Nevertheless, characterisation of the mechanical and biological functions of 3D printed constructs with respect to their host tissues is often limited and remains a restriction towards their translation into clinical practice. This review aims to provide an update on the current status of AM to mimic the mechanical properties of CTs, with focus on arterial tissue, articular cartilage and bone, from the perspective of printing platforms, biomaterial properties, and topological design. Furthermore, the grand challenges associated with the AM of CT replacements and their subsequent regulatory requirements are discussed to aid further development of reliable and effective implants.