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A new approach to characterize ITZ between microfiber and cement matrix is reported. Results show that microstructure of hydrated cement paste is highly modified in the vicinity of microfibers, with higher porosity and less anhydrous cement. ITZ can extend up to 100 μm from the interface into the matrix. The larger extent of ITZ suggests that perturbation due to inclusion of microfibers to packing of cement grains is severer than that due to inclusion of aggregates. Furthermore, ITZ between microfiber and cement matrix is highly heterogeneous along its axial direction. Existing ITZ analysis methods performed on 2-D cross-sectional plane intersecting with fiber axis thus can lead to errors and uncertainties. Mechanical properties of ITZ between microfiber and cement matrix are anisotropic. Stiffness and ductility of ITZ in the radial direction are 31% and 28% higher than that in the tangential direction, respectively. Accepted version

A simultaneous estimation of the vertical and horizontal autocorrelation distances (ACDs) for geotechnical properties under the condition of limited data (fewer than one hundred data points) is not well studied. This paper evaluates the performance of the maximum likelihood estimator (MLE) in estimating autocorrelation distances using some simulated data. The effect of the autocorrelation structure on the accuracy of ACD estimation is also investigated. It is found that MLE may produce highly biased estimations if limited data are available. Hence, a clustered borehole layout scheme and a resampling method are proposed to improve the estimation accuracy. The methods are illustrated using some simulated data, standard penetration test (SPT) data and cone penetration test (CPT) data. It is found that the clustered borehole layout scheme and resampling method yield more accurate estimations of ACDs in analyses using both the simulated data and real data. Accepted version

The decision-making process in flood mitigation typically involves many factors reflecting flood severity, flood vulnerability and the cost of the mitigation measures. In this PhD study, a Multi-Criteria Decision Analysis (MCDA) decision framework for optimal decision making in flood protection design, specifically levees are developed. This framework accounts for climate change, increasing urbanization, and evolving socio-economic features of the flood plain, and as well as for uncertainties in rainfall predictions. The changing climate and the growing urbanization alter the flood frequencies with large uncertainties that strongly influence future projections. These uncertainties make the flood mitigation decision more complex. Thus, uncertainties involved in both current and future conditions are quantified via computation of the expected values of change indices developed. The MCDA uses as its criteria the annual expected loss, graduality, a newly developed Socio-Economic Vulnerability Index (SEVI) and levee construction cost. It is further demonstrated for a central basin of Jakarta, Indonesia. The annual expected loss at current conditions is calculated with recorded rainfall data as fitted using the Log Pearson Type III distribution. The graduality represents the severity with change in discharge as reflected by the deviation from linearity between percentile discharge and percentile loss values. The SEVI reflects the social and economic impact on the flood affected population via scaling with the flood inundation area and depth while capturing uncertainty in the rainfall forecasting. Temporal change factors (CF) as calculated from a statistically downscaled global gridded rainfall projection, the NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP) are applied for future rainfall (specifically 2031-2070). The uncertainty across the 20 Global Climate Models (GCM’s) is quantified via an expected CF scaled across the GCMs via an inverse distance method. Landsat data over year 1989-2009 is classified into various land use, including urban, and is used to develop urbanization trends and projected to year 2050. The impact of climate change and urbanization are incorporated in the MCDA flood decision framework through the criteria being recalculated under the future conditions. The changing climate, growing urbanization and the socio-economic features, are shown to drive the best choice of levee protection plan towards higher protection levels under the future time period considered. Inclusion of socio-economic factors is also shown to change the best plan. The developed methodology and the results are expected to guide decision making in flood mitigation and can be extended to include decision-making on other flood mitigation measures as well as additional sources of uncertainties. Doctor of Philosophy (IGS)

Iodinated trihalomethanes (I-THMs) and iodoacids could be formed as iodinated disinfection by-products (I-DBPs) during water treatment and water reclamation processes. To develop a cost-effective strategy for post-formation mitigation of I-DBPs, the degradation of I-THMs and iodoacids in water by UV254, UV/H2O2, and UV/PS (persulfate) processes was extensively investigated in this study. The effect of pH, and/or oxidant dose, matrix species, and different types of water on the degradation kinetics of I-DBPs in the UV254, UV/H2O2, and UV/PS processes was examined. A quantitative structure-reactivity relationship (QSAR) model for direct photolysis of I-DBPs was established to correlate the chemical activities with molecular structures. A steady-state kinetic model was developed to predict the degradation rate of I-THMs in the UV/H2O2 process. Using probe compounds, the respective contribution of UV, SO4∙‒ and HO∙ for iodoacid removal in the UV/PS process were quantitatively determined. Photodegradation end by-products for each process were also identified. Total cost of electrical energy and oxidant was calculated to evaluate the energy efficiencies of UV, UV/H2O2, and UV/PS processes for I-DBPs removal. Doctor of Philosophy (CEE)

The global energy demand has escalated during last few decades due to the population growth, urbanization and industrialization. On the other side, rapid and continuous exploitation of non-renewable fossil fuels have raised the concerns on environmental degradation. This necessitates developing efficient energy storage systems besides energy production to help match the supply and demand. Carbon materials have been extensively studied as electrodes for energy storage applications. However, carbon materials used as electrodes in commercial energy storage systems at present are derived from non-renewable fossil fuels. Thus, there is need to explore alternative sustainable carbon precursors. This will help reduce the sole dependency on nonrenewable fossil fuels and also contribute in creating healthy environment. Biomass are rich in carbon content, and are low cost, easily available, abundant, renewable and environmentally-friendly. Food waste is an inevitable by-product produced in different stages of the food supply chain. Fruit peels waste as bio-waste are neglected reusable resource which offer a big potential for employing it as precursor for the production of value-added products such as porous carbons. Therefore, comprehensive study is needed to evaluate the potential of employing this underutilized sustainable resource for preparation of value-added useable products such as porous carbon. Further investigations are also needed to evaluate the electrochemical performance of these carbons as electrodes for energy storage applications, and development of high performance energy storage devices. This has motivated this study to explore fruit peels waste as precursor materials for energy storage applications such as vanadium redox flow battery (VRB) and high energy supercapacitors. High surface area activated carbons (ACs) were synthesized by carbonization followed by chemical activation from the five screened precursors, and the assynthesized ACs were subjected to extensive characterizations. Two AC samples synthesized from orange peels waste and lychee peels waste were further screened for evaluating them as electrode materials for energy storage applications. The orange peel-derived ACs modified graphite electrodes demonstrate improved electrocatalytic activity in both positive and negative side redox couples compared with the pristine graphite electrode. The improved electrode activities are attributed to the synergistic effects of high surface area of the ACs and rich oxygen functionalities on the surface of ACs. The results suggest the OP-ACs to be promising electrodes for VRB applications and can be incorporated into making conducting plastics electrode to lower the VRB cell stack weight and cost. The lithium ion capacitors (LICs) fabricated using OP-AC2 with pre-lithiated graphite (LiC6) delivered specific energy of ~106 Wh kg–1 . A systematic improvement from the specific energy of ~8 to 106 Wh kg–1 is noted from aqueous to LIC assembly. The other porous carbon synthesized from lychee peel waste (LP-AC) with surface area of 1601 m2 g -1 was evaluated as electrode material for supercapacitors in symmetric (LP-AC||LP-AC) and asymmetric (Gr/PANI||LP-AC) cell configurations. Performance tests showed that the asymmetric cell assembly could deliver specific capacitance of ~141 F g-1 at 0.5 A g-1 and specific energy to ~50 Wh kg-1 as compared to the specific capacitance of 105 F g-1 at a current density of 0.25 A g–1 and specific energy of 9.4 Wh kg-1 for the symmetric cell configuration. The asymmetric cell also showed good cycling stability with ~88% of the initial specific capacitance retained after 5000 cycles. To sum up, this study successfully demonstrated the feasibility of converting selected fruit peels waste to value-added porous carbons as promising electrodes for energy storage applications. For the first time, this study evaluated performance of the OP-AC and the T-OP-AC modified electrodes for VRB applications. The fabrication of whole LIC assembly using OP-AC to deliver high energy was also reported for the first time. For the first time, the porous AC synthesized from a new precursor, i.e. lychee peel, was reported as pseudocapacitive electrode for aqueous supercapacitors. The utilization of this renewable resource contributes not only in waste management but also generates value-added products for promising applications, and contribute in reducing sole dependency on fossil fuels for energy. Doctor of Philosophy (CEE)

Non-rectangular reinforced concrete (RC) squat walls are widely used in existing buildings and safety-related nuclear facilities. Compared with rectangular walls, these walls possess significant stiffness in both principal directions, which contributes to their resistance to biaxial bending actions during earthquakes. In spite of their popularity and practicability, the experimental data on these non-rectangular RC squat walls are rather sparse, especially for walls subjected to non-principal bending action. Moreover, current design procedures are developed for rectangular slender walls, which have been found by many researchers to be unsuitable for non-rectangular RC squat walls. To improve the understanding of the seismic behavior of such walls, both experimental and analytical investigations are conducted in this study. Doctor of Philosophy (CEE)

This thesis presents new in-depth discussions and design methods for high strength concrete (HSC) and steel fibre reinforced concrete (SFRC) slabs that are subjected to punching shear. Experimental programmes of 22 full-scale slabs are presented to accompany the discussions and the new design methods proposed in this thesis. All of the 22 slab specimens were constructed with high strength concrete. Some of the advantages of using high strength concrete compared to normal strength concrete include an increase in cracking load of the slab and a reduction in deflection at service load level due to higher tensile strength and higher elastic modulus of high strength concrete. This research focuses on the investigation of the influences of two main structural parameters on the punching shear strength of a slab. The two parameters concerning this research are (1) the effect of low flexural reinforcement ratios, and (2) the influence of a new type of fibres - the double hooked end fibre. Recently, several researchers have addressed and investigated the influences of these parameters; however, more research are still needed. Therefore, the following paragraphs provide a brief summary of this thesis that includes both experimental and analytical works. First, punching shear tests of 12 high-strength concrete slabs (f’c > 95 MPa) with various flexural reinforcement ratios and column aspect ratios are presented. The dimensions of the specimens are 2.2 × 2.2 × 0.15 m and 2.7 × 2.2 × 0.15 m. The resulting slab data represent a complete set of slab specimens having low to high reinforcement ratios. The purpose of the tests is to investigate if Code equations (ACI 318, Eurocode 2) for punching shear overestimate the actual punching shear strengths of slabs that are provided with low amount of flexural reinforcement or low reinforcement ratio. Other influencing factors, such as column rectangularity ratio, concrete strength, and size (thickness) effect are also addressed. The author’s new experimental results will be combined with 355 existing published data and together they will be used to evaluate the accuracy and safety of the ACI 318-14 and Eurocode 2 methods for punching shear, as well as some methods proposed by other researchers. Second, punching shear tests of 10 steel fibre reinforced concrete (SFRC) slabs tested under punching shear loads are presented. The dimensions of the specimens are 2.2 × 2.2 × 0.15 m. The influence of high strength concrete (f’c ≥ 80 MPa) and a new type of steel fibre (the double hooked end fibre) were investigated. The fibre contents were varied from zero to 1.2% volume fraction for each set of the reinforcement ratio ρ. The reinforcement ratio ρ was varied from ρ = 0.9% to ρ = 1.4%. Key attributes, such as: ultimate state and serviceability performances, of these high strength SFRC slabs are discussed. The experimental results highlight that high strength SFRC enhances the slab performance in many aspects. As the fibre volume Vf was increased from 0% to 1.2% or to an equivalent fibre dosage of 93.6 kg/m3, the flexural stiffness of the slabs increased while both the deflections and crack widths reduced. At the ultimate state, the punching shear strength increased by up to 156% compared to non-fibrous concrete slabs, which is significantly higher than the increment introduced by conventional single hooked-end fibres; the ductility and energy absorption capacity of the slabs were also significantly improved. Comparisons of design methods with the experimental results show that the TR34 method by the Concrete Society performs very well while the yield line theory overestimates the strengths of the slabs. The Model Code 2010 method is unconservative. Finally, some relevant design recommendations are given. New design methods are proposed, they will be shown to be very reliable and accurate for calculating the punching shear strength of both reinforced concrete and steel fibre reinforced concrete slabs. Doctor of Philosophy

The Western Maritime Continent (WMC) is recognized to have major weather and climate importance on both global and local scales. However, because of excess convection and complex topography, the region faces severe climate and weather modeling challenges. Further, the region has scarce station data, and Global Climate Models (GCMs) such as the Hadley Centre Global Atmospheric Model (HadGAM1) have been systematically found to incorrectly model precipitation. Thus, it is essential that WMC is properly represented by Regional Climate Models (RCMs) to capture and reproduce regional precipitation correctly. The discrepancy in GCM to accurately modeling rainfall over the WMC region results in errors that propagate to both the tropics and extra-tropics precipitation output as well. The RCMs have been observed to provide "added information" over the GCM data as they consider local topography and climate. The "added information" by RCM was used in three studies conducted in this thesis. In the first study, an integrated downscaling approach, i.e., combination of statistical and dynamical downscaling was applied over the WMC. RCM downscaled predictors having better spatial resolution capture the local information more appropriately and were used as input to a statistical downscaling model. The RCM used was the Weather Research and Forecasting (WRF) model. Integrated downscaling approach would thus fill data gap over data sparse regions of the WMC with a good quality downscaled dataset, thus, enabling a better analysis of precipitation for impact analysis. The most noticeable improvements are for Singapore location where using WRF predictors resulted in an RMSE value of 1.37 (0.81) for mean monthly rainfall for validation (calibration) period while R2 predictors had a much larger RMSE of 3.41 (3.86). In the second study, one of the outputs of CMIP5 GCM model output data, i.e., CESM1 bias corrected using ECMWF by NCAR was provided to WRF to downscale precipitation over the year 2030 to 2060 for RCP 4.5 and RCP 8.5 scenarios. Furthermore, the WRF precipitation was extracted and was used to generate future IDF curves over three locations in the WMC. In the final study, the Wards method was used to find clusters across 43 locations in WMC. The spatial-temporal groups formed were explained using CHIRPS (for historical) and WRF CMIP5 (for future). This is among the few studies done over WMC that utilizes outputs from two different RCMs to model future changes in extreme rainfall intensity. The output from the study would be significant in planning drainages and accessing future flooding considering the climate change. A region-specific parametrization scheme validated with observation data to capture convective precipitation was found for WRF and used for the three different studies. An integrated approach capable of producing better mean and extreme rainfall statistics than via conventional statistical downscaling from GCM was verified in the first study over all the four locations. In the second study, bias-corrected IDF curves were constructed for the two RCPs 4.5 and 8.5 scenarios. Significant increments in precipitation were observed over the three locations in WMC. The WRF-IDF was further compared to CORDEX-IDF, and it was noted that WRF predicted a greater increment in Intensity as compared to CORDEX. Both WRF and CORDEX outputs are considered as different realizations of the two-member ensemble. Hence these two realizations can be used to access the probable uncertainty in future IDF curves. The predicted increment in extreme rainfall intensity by RCP 8.5 was larger compared to RCP 4.5 and historical for almost all the locations and return periods. For Singapore (100 year RP and RCP 8.5) average intensity increase was 36.1% for WRF-IDF at RCP 8.5 while it was 16.8% for CORDEX-IDF. Over Jakarta (100 year RP) the RCP 8.5 WRF-IDF showed 52.5% average increment while the WRF-IDF showed 74% increase in average intensity. Lastly, the cluster analysis revealed some interesting new grouping in both spatial and temporal dimensions from the third study. This is the first study over WMC that examined the changes in spatial and temporal monthly precipitation using future RCP downscaled CMIP5 GCM data. It was observed that Spatial Groups (SG) formed for WRF-CMIP5 (RCP 4.5 and RCP 8.5) were very different from historical. The difference between SGs would signify changes in precipitation over the next 25 years. While comparing the SGs for RCP 4.5 and RCP 8.5, it was observed that of all the landmasses, Borneo would see the most significant redistribution and would become more homogenous in its rainfall pattern. Doctor of Philosophy (CEE)

A rail system is the most important land transportation. Its safety and stability are critical. The rails are installed on discrete supports. In practice, there are several defects, such as loosening of fasteners and degradation of sleepers and blasters, frequently occurred on these supports. Currently, the detection of defects relies mainly on visual inspection by trained personal. This study proposes a workable solution to detect these defects in view of their significant influences on the support stiffness between the rails and the discrete supports. The method only requires one sensor mounted on a moving device. Based on the numerical and experimental examples, degraded supports are located accurately, irrespective of the spatial distribution of degraded supports. The method performs well under periodic impact and random excitation and is far more efficient and accurate than visual inspection. Doctor of Philosophy (CEE)

A novel idea of using carbon nanofibers (CNFs) to strengthen the interface transition zone (ITZ) and to enhance the interface frictional bond strength between polyethylene (PE) fibers and cement matrix was proposed and realized by coating CNFs on surface of PE fibers through hydrophobic interactions. A strain hardening ultra-high-performance concrete (SHUHPC) incorporating such CNF-coated PE fibers was developed. The resulting CNF-SHUHPC has a compressive strength over 150 MPa and exhibits 15% enhancement in tensile strength and 20% improvement in tensile strain capacity as compared to the control SHUHPC. Single fiber pullout tests showed the interface frictional bond strength of the CNF-coated PE fiber was increased by 22%, which is attributed to CNFs strengthen the ITZ by filling nano-pores and bridging nano-cracks resulting in denser microstructure and higher crack resistance against fiber pullout as revealed by the micrographs and Nanoindentation test results. Master of Engineering (CEE)

Solvent-resistant nanofiltration (SRNF) is an emerging membrane-based separation technology that can separate molecules of 200-1000 Da in various organic solvents efficiently. It has the potential to replace or be combined with traditional separation processes in industry to lower energy consumption and reduce waste. As hollow fiber membranes can offer advantages over flat sheet membranes and are not known to be commercially available for SRNF applications, this study aims to develop hollow fiber membranes that can perform nanofiltration in challenging polar aprotic solvents such as dimethylformamide (DMF) at a lower operating pressure than existing SRNF membranes. Polyamide-imide hollow fibers were fabricated by non-solvent induced phase separation and crosslinked using 3-aminopropyl trimethoxysilane (APTMS) so that they were stable in DMF. The crosslinked membranes were characterized by their gel content, swelling property, contact angle and mechanical properties. A conditioning treatment with either isopropanol (IPA) or deionized (DI) water was found to affect the morphology and performance of the membranes. Nanofiltration tests were carried out under 2 bar using Rose Bengal (1017 Da) in IPA and DMF. The membranes were tested in continuous operation for 7 days and stable performance in terms of flux and rejection could be attained, showing their potential to be applied in SRNF processes effectively. Master of Engineering (CEE)

The feasibility of using engineered cementitious composites (ECC) in joint cores of reinforced-concrete (RC) beam–column sub-assemblages as a means to enhance seismic behaviour is evaluated. Four RC beam–column sub-assemblages are constructed and tested under lateral cyclic loading. One RC beam–column sub-assemblage with normal concrete in the joint and one RC sub-assemblage with ECC in the joint are designed to gravity loads; neither type has transverse reinforcement in the joint core. Similarly, one RC sub-assemblage with normal concrete in the joint and one with ECC in the joint are designed for seismic provisions, but the latter has no transverse reinforcement in the joint. The test programme thereby allows direct comparison of the structural performance of ECC joints with concrete joints for beam–column sub-assemblages for both gravity and seismic design situations. Results show that the use of ECC joints significantly changes the behaviour of the joint from brittle to ductile. Both ECC specimens exhibit superior damage tolerance, with limited shear distortion and multiple fine cracks in the joints, even though no transverse reinforcement is provided in the joint. Moreover, specimens with ECC joints demonstrate improved bond behaviour in early loading cycles.

Performances of a braced cut-and-cover excavation system for mass rapid transit (MRT) stations of the Downtown Line Stage 2 in Singapore are presented. The excavation was carried out in the Bukit Timah granitic (BTG) residual soils and characterized by significant groundwater drawdown, due to dewatering work in complex site conditions, insufficient effective waterproof measures and more permeable soils. A two-dimensional numerical model was developed for back analysis of retaining wall movement and ground surface settlement. Comparisons of these measured excavation responses with the calculated performances were carried out, upon which the numerical simulation procedures were calibrated. In addition, the influences of groundwater drawdown on the wall deflection and ground surface settlement were numerically investigated and summarized. The performances were also compared with some commonly used empirical charts, and the results indicated that these charts are less applicable for cases with significant groundwater drawdowns. It is expected that these general behaviors will provide useful references and insights for future projects involving excavation in BTG residual soils under significant groundwater drawdowns. Keywords: Braced excavation, Bukit Timah granitic (BTG) residual soil, Wall deflection, Groundwater drawdown, Empirical charts

Container terminals play a critical role in maritime supply chains. However, they show vulnerabilities to severe weather events due to the sea–land interface locations. Previous severe weather risk analysis focused more on larger assessment units, such as regions and cities. Limited studies assessed severe weather risks on a smaller scale of seaports. This paper aims to propose a severe weather-induced container terminal loss estimation framework. Based on a container terminal operation simulation model, monthly average loss and single event-induced loss are obtained by using historical hazard records and terminal operation records as model inputs. By studying the Port of Shenzhen as the case study, we find that the fog events in March lead to the longest monthly port downtime and the highest monthly severe weather-induced economic losses in the studied port. The monthly average loss is estimated to be 30 million USD, accounting for 20% of the intact income. The worst-case scenario is found to be a red-signal typhoon attack which results in nearly 20% decrease in the month’s income. The results provide useful references for various container terminal stakeholders in severe weather risk management. Accepted version

The drag coefficients of one mature Khaya Senegalensis tree and one Eugenia Grandis tree in Singapore were analysed using computational fluid dynamics (CFD) modelling and validated with field measurements. For the numerical method, an innovative laser scanning approach was used to generate the tree geometries and to calculate the three-dimensional (3D) leaf area density distribution within the canopies. The canopies were represented by multiple porous domains and the turbulent effect of leaves was simulated by source and sink terms as a function of the calculated leaf area density. Computational fluid dynamics analyses using ANSYS 17.2 software were carried out on both leafless and leafed tree models. Three turbulent models, the Realizable k-ε model, Transition Shear Stress Transport model and Reynolds Stress Model were compared, and it was found that the differences in the drag forces among the turbulent models were negligible when they were meshed appropriately based on the grid independence study. The computed drag coefficient of the Khaya Senegalensis tree and the Eugenia Grandis tree from CFD modelling were similar within the range between 0.6 and 0.7. From field monitoring including the wind velocity and stem strains, the drag coefficients of both trees were calculated to be 0.51 and 0.40. Possible reasons causing the difference and limitations of the numerical method are discussed. Accepted version

Seaports are critical infrastructure systems in the international economy. They are at the same time vulnerable to various types of natural and man-made catastrophes due to their special coastal and low-lying locations. Traditional catastrophe risk analyses focused more on regions, port cities, and port communities. Limited studies assessed catastrophe risks on ports as a specific system. This paper aims to develop a catastrophe-induced port loss estimation framework, based on a port operation simulation model, actual terminal records and historical hazard records. By using the typhoon hazard and the Port of Shenzhen as a case study, we find that (1) the worst-case scenario of a typhoon impact could cause a total loss of US$0.91 billion for a terminal with 16 berths; and (2) the annual predicted typhoon-induced loss for the same terminal for the next 5 years will reach approximately US$64 million, accounting for 19.7% of the terminal net profit in 2015. The results provide useful references for various port stakeholders in catastrophe risk assessment and mitigation. Accepted version

This paper presents a series of investigative studies, mainly parametric and numerical, into various issues related to the practical application of the wave propagation (WP) technique in monitoring of concrete curing using smart material (PZT). This paper is an extension of a range of experimental studies presented in the authors’ recent publication. Coupled field finite element (FE) simulation of the PZT-structure interaction in WP technique is conducted on mortar and concrete specimens. Identification of the pressure wave (P-wave) and the surface wave (R-wave) velocities simulated in the FE model is attempted. Results are found to be matching closely with the experiment. The verified FE model, together with the theoretical model are then used to perform parametric study on selected factors related to the practical application of the technique, in particular those uncontrollable in the experiment, including the dynamic modulus of elasticity, the Poisson’s ratio and the damping coefficient. Further experimental and analytical studies on the effect of varying temperature and humidity are also presented. A semi-analytical model previously proposed by the authors is finally adopted to generate a strength calibration chart for concrete with different coarse aggregates. The theoretical and FE models are proven to be useful alternatives to the experiment, which can be used in future design and optimization of the PZT based WP technique in monitoring of concrete curing. Accepted version

The performance of open-ended piles can be different from that of closed piles due to the effect of soil plugging. This paper presents the results of a large-scale field pile load test conducted on an open-ended pile in clay under static compressive loads. A prestressed high-strength concrete pipe pile with an outer diameter of 400 mm and a wall thickness of 75 mm was instrumented with strain sensors and installed in a marine deposit for static load testing. The measured load-transfer data during pile installation and the pile load test results are reported and analysed. The data show that the pile was in a partially plugged condition during jacking and behaved in a fully plugged mode in the static load test. The measured ultimate shaft resistance and total resistance of the test pile were 659 and 1180 kN, respectively, which were smaller than the values calculated using a previously proposed method. The back-calculated α and β values (as used in the α and β methods) for axial pile capacity in marine deposits were 0·42 and 0·56, respectively.

The flat-top partition of unity method can obtain a stiffness matrix with a small condition number and avoid the linear dependence problem. We aimed to extend the flat-top partition of unity method to rock dynamic analyses to simulate the influence of discontinuity and dynamic loading. Therefore, the flat-top partition of unity method was coupled with the discontinuous deformation analysis. In this paper, after the presentation of the mesh construction, the inertia force and contact algorithm for flat-top partition of unity-based discontinuous deformation analysis, several numerical examples are presented to verify the accuracy and efficiency of the method. Accepted version

This study focuses on the development of a new strain-hardening composite (SHC) involving carbonated reactive MgO cement (RMC) and fly ash (FA) as the main binder. Rheological properties of the developed composites were investigated by varying FA and water contents to achieve desirable fiber dispersion. A suitable mix design, in which polyvinyl alcohol (PVA) fibers were introduced to provide tensile ductility, was determined. The effect of key parameters such as w/b ratio and curing age on the mechanical properties of carbonated RMC-SHC was evaluated. Adequate binder content and w/b ratio was necessary for desirable fiber dispersion. Lower water contents and longer curing ages contributed to the strength development of RMC-SHC by improving the fiber-matrix interface bond and enhancing the formation of a dense carbonate network. MOE (Min. of Education, S’pore) Accepted version

The flow past a circular cylinder that is rotating retrograde near a turbulent wall boundary layer at Re = 10 000 has been investigated experimentally using particle image velocimetry (PIV). The cylinder rotates in retrograde direction with different rotation ratios from α = 0 to 2, where α is defined as the ratio of the peripheral speed on the cylinder surface divided by the free-stream velocity. The gap ratio, G * = G/D, is varied between 0 and 1.6, where G is the gap between the cylinder and the plane wall, and D is the cylinder diameter. The flow structure is greatly modified due to the influence of wall proximity and cylinder rotation, notably the onset/suppression, frequency and strength of vortex shedding. Similar to a near-wall stationary cylinder, there exists a critical gap ratio (about 0.4) below which periodic vortex shedding from the cylinder is suppressed. On the other hand, the cylinder rotation causes vortex shedding to cease at α ≥ 1.6, which is slightly lower than the reported value of α ≈ 2 in the literature on rotating cylinder in uniform flow. However, reducing G * and increasing α do not always favor the suppression of vortex shedding. In fact, cylinder rotation promotes vortex shedding over a certain range (α < 1). As α increases, the length of recirculation region behind the cylinder, which is indicated by the movement of the mean saddle point, decreases almost linearly. The effects of wall proximity and cylinder rotation are also evident on the ensemble-averaged flow field, such as the turbulent kinetic energy and Reynolds shear stress. Accepted version

The ability to motivate and retain seafarers is a critical manpower issue in view of global labour shortage and high turnover rate among seafarers. The objective of this paper is to analyse the core determinants of job satisfaction and performance of seafarers. A survey was administered on 116 seafaring officers and the obtained data were analysed using structural equation modelling. The results show that job satisfaction is considerably correlated with job performance of seafarers. In addition, the amount of stress associated with working onboard a ship and attractiveness of rewards are key determinants of job satisfaction. The dispositions of seafarers and appeal of the job design also have considerable impacts on job satisfaction. Based on literature review and post-survey interviews, a management model consisting of policies and strategies to motivate and retain seafarers is proposed. Accepted version

Dismantling end-of-life ships in an environmentally sound and safe manner is of great concern as well as being a major challenge nowadays. When dismantling the vessel, on-board hazardous materials such as asbestos, polychlorinated biphenyls (PCBs), glass fibre, solid foam and waste oil can incur severe negative implications on the environment and human health. The characteristics and harm of on-board hazardous materials are profiled in this paper. Current removal and disposal methods of hazardous materials are analysed. Further practical measures and suggestions to deal with the hazardous materials in the ship breaking yards are proposed. Two case studies about green disposal of the main hazardous materials during shipbreaking are presented. Both of the two companies are following Hong Kong Convention and verified by DNV-GL classification, which makes the recycling procedures of hazardous materials are quite similar to each other. In essence, more attention should be paid to the disposal of hazardous materials as integral to safe and environmentally sound practices when breaking the ships. Accepted version

Load-carrying cruciform fillet welded joints configuration is frequently encountered in many welded structures. Different from non-load-carrying joints, the crack in load-carrying joints can propagate from the weld root or from the weld toe. Hence, the crack propagation location is critical for a given weld size, transverse and main plates thickness. In this study, a finite element (FE) mesh generator developed previously is extended to generate 3-D models of load-carrying joints containing cracks at the weld root and the weld toe. Then, extensive parametric study is carried out to calculate the stress intensity factors (SIFs). Corresponding SIF equations are proposed according to multiple regression analysis. Based on these equations obtained for the weld root and weld toe cracks, the critical crack and weld sizes at which the crack propagates from the weld root to the weld toe are determined. Accepted version

Purpose As an application of self-service technology, automated parcel station (APS) is emerging as a logistics innovation to address the inefficiency and delivery failure in conventional home delivery. However, the long-term viability of APS depends on the consumers’ acceptance of such concept. In response, the purpose of this paper is to conduct a behavioural study on consumers’ adoption of self-collection service via APS. Design/methodology/approach By synthesising theoretical insights from the innovation diffusion literature and attitude theories, a conceptual model is developed and empirically validated. Perceived characteristics of APS are present to directly influence the consumers’ adoption intention, or indirectly through attitude. A total of 170 valid responses are collected from a survey conducted in Singapore and the data are analysed using structural equation modelling. Findings Consumers’ favourable attitude and perceived relative advantage of APS directly lead to stronger adoption intention. On the contrary, consumers’ perceptions on compatibility and trialability and on complexity indirectly influence their adoption intention via attitude, in a positive and in a negative way, respectively. Additionally, attitude is found to be the most influential factor contributing to consumers’ adoption intention. Research limitations/implications The scope of this paper is limited to e-consumers’ initial adoption decision. Future research should examine the consumers’ adoption behaviour further down the innovation adoption process, such as continuance and commitment. Originality/value This research conceptualises and validates the consumers’ adoption behaviour of APS from a synthesised view of innovation diffusion and attitude theories, theoretically and empirically contributing to the field of study on logistics innovations from the consumers’ perspective.

Bayesian Network (BN) is often criticized for demanding a large number of crisp/exact/precise conditional probability numbers which, due to the lack of statistics, have to be obtained through experts’ judgment. These exact probability numbers provided by the experts often carry a high level of epistemic uncertainty due to the incompleteness of human knowledge, not to mention the hardness in obtaining them in the first place. The existence of uncertainty in risk modelling was well recognized but seldom discussed. This paper explores the extension of BN with interval probabilities to the modelling of maritime accidents, which allows for the quantification of the epistemic uncertainty. Ship collision is chosen for case study for the strategic importance of navigational safety. The user friendly linguistic terms defined with interval scales were used for elicitation of interval conditional probabilities from industry experts. Inferences were made directly with the interval probabilities with the GL2U algorithm. Meanwhile, the interval probabilities were converted into point probabilities and computed with the traditional BN method for comparison, which were all shown to be within the ranges of the calculated posterior intervals probability. Results with inputs from different experts reveal discrepancies, which in turn verify the existence of uncertainty in risk modelling. A discussion was also provided on how the uncertainty in risk assessment propagates to the decision making process and influences the ranking of potential risk control options. Accepted version

The plastic collapse loads of cracked circular hollow section (CHS) T/Y-joints under in-plane and out-of-plane bending are investigated using finite element (FE) analyses. An in-house 3D FE mesh generator is specifically developed to create the mesh models of the cracked joints containing a semi-elliptical surface crack located at the weld toe of the chord. Mesh convergence tests are then carried out to check the accuracy of the generated mesh models. The in-plane and out-of-plane plastic collapse moments of uncracked CHS T/Y-joints are calculated and compared with results obtained from three codes and experimental data. The comparison shows that the plastic collapse moments of uncracked CHS T/Y-joints obtained in this study are accurate and reliable. Subsequently, an extensive parametric study is carried out to investigate the plastic collapse moments of cracked CHS T/Y-joints under in-plane and out-of-plane bending. It is found that the in-plane and out-of-plane plastic collapse moments may decrease by up to 35.1% and 33.6% respectively when the crack area Anc reaches 25% of the intersectional area, t0*lw. Finally, two lower bound strength reduction factor FAR equations for cracked CHS T/Y-joints under in-plane and out-of-plane bending are proposed.

A two-degrees-of-freedom (2-DoF) dynamic model is proposed to predict the response of reinforced concrete (RC) slabs subjected to low-velocity impact. In this model, the slab stiffness is calculated based on its dynamic load–displacement curve, which is built using moment–curvature analysis and critical shear crack theory. The contact between the impactor and the impacted RC slab is modelled with an elastic spring and a viscous damper. The effectiveness of the 2-DoF model was verified by comparisons with experimental data. The results obtained from the 2-DoF model are further processed to show the distribution of impact energy during the impact process, and a simple method is recommended for a quick estimation of the energy capacity of RC slabs.

Structural reinforced concrete (RC) walls can have very different lengths and widths. Previous investigations have focused on the seismic properties of structural RC walls in the strong axis in which the length of the wall is greater than the width of the wall. The seismic behaviour of structural RC walls in the weak axis, where the wall length is less than its width, is insufficiently investigated. This paper reports on experimental studies on the seismic behaviour of two non-rectangular RC walls loaded in the weak axis. The experimental results are presented in terms of cracking patterns, failure mechanisms, hysteresis responses, the component of deformation and the distributions of vertical strains in the flange. The experimental results are discussed, and emphasise the accuracy of existing design methods for non-rectangular RC walls in the weak axis, including design methods for the stiffness, the shear lag effect and the shear strength.

Clay minerals and metal oxides, as important parts of the soil matrix, play crucial roles in the development of microbial communities. However, the mechanism underlying such a process, particularly on the formation of soil biofilm, remains poorly understood. Here, we investigated the effects of montmorillonite, kaolinite, and goethite on the biofilm formation of the representative soil bacteria Bacillus subtilis. The bacterial biofilm formation in goethite was found to be impaired in the initial 24 h but burst at 48 h in the liquid–air interface. Confocal laser scanning microscopy showed that the biofilm biomass in goethite was 3–16 times that of the control, montmorillonite, and kaolinite at 48 h. Live/Dead staining showed that cells had the highest death rate of 60% after 4 h of contact with goethite, followed by kaolinite and montmorillonite. Atomic force microscopy showed that the interaction between goethite and bacteria may injure bacterial cells by puncturing cell wall, leading to the swarming of bacteria toward the liquid–air interface. Additionally, the expressions of abrB and sinR, key players in regulating the biofilm formation, were upregulated at 24 h and downregulated at 48 h in goethite, indicating the initial adaptation of the cells to minerals. A model was proposed to describe the effects of goethite on the biofilm formation. Our findings may facilitate a better understanding of the roles of soil clays in biofilm development and the manipulation of bacterial compositions through controlling the biofilm in soils., Soil: Mineral effects on biofilms The effect of three soil minerals on biofilm production is clarified by research using the common soil bacterium Bacillus subtilis. The mineral composition of soil is known to affect biofilm production, but the mechanisms underpinning minerals’ influences have not been well studied. Peng Cai and colleagues at Huazhong Agricultural University in China, with co-workers in the United States and Singapore, studied Bacillus subtilis growing in the presence of the minerals montmorillonite, kaolinite, and goethite. Their results suggest the minerals, especially goethite, can encourage biofilm formation by promoting the bursting of bacterial cells. The effect of goethite was attributed to the size of its grains being generally smaller than the bacterial cells. By quantifying the effect of these minerals, the research will assist understanding of biofilm formation and the growth and persistence of bacterial populations in soils.

In Singapore, two thirds of the land area is underlain by residual soils. One distinct characteristic of residual soils is its unsaturated nature. The relationships of shear modulus and damping ratio with shear strain for residual soils may differ from transported soils and have not been fully investigated. This study aims to investigate shear stiffness and damping ratio properties of residual soils under cyclic simple shear loading in both saturated and unsaturated conditions. Doctor of Philosophy (CEE)

Circular hollow sections (CHS) are widely adopted in fixed jacket and topside structures due to their excellent structural and mechanical properties. Virtually in almost all off-shore structures, one of the main design considerations when using CHS is to optimize the structural joints which are susceptible to fatigue failure due the dynamic and cyclic loading natural of the structures. Recently, partially overlapped CHS tubular K-joints become more and more popular due to their optimum strengths when compared to other alternative joint configurations such as non-overlapped (gapped) or completely overlapped K-joints. However, in the past, few research works were carried out to study the fatigue behaviour of partially overlapped CHS K-joints. In fact, currently, only a very limited information regarding the fatigue life of CHS overlapped K-joints are available. Hence, there is a need to investigate the stress concentration factors (SCF) and the hot spot stress (HSS) distributions of this kind of joints in the current research. Doctor of Philosophy (CEE)

Given the fact that often low-probability extreme events can lead to disastrous consequences, the simulation and prior assessment of the civil engineering systems and critical infrastructure systems in such events are very important. To assess the system performance subjected to dynamic excitations realistically, stochastic system analyses considering all the important uncertainties including both aleatory and epistemic uncertainties, and modeling errors, which require a huge number of random variables, need to be performed. In this thesis, the focus is on the development of new stochastic simulation algorithms for Bayesian model updating, robust reliability (or its compliment "failure" probability) updating, extreme-event simulation and probability computation, conditional failure sample simulation, and their applications to the evaluation of reliability, seismic risk and loss assessment of civil engineering structures. A new stochastic simulation based Bayesian model updating technique is developed to update a stochastic dynamic system model based on measured system response data. The technique is extended and a new stochastic simulation approach is proposed using system response data for computing the updated robust reliability of a stochastic dynamic system when it is subjected to uncertain future stochastic excitations. Next, a new fully probabilistic algorithm is developed for a comprehensive seismic risk and loss analysis and investigation. The newly developed computational method to update the robust stochastic dynamic system reliability based on system response data is integrated with the newly developed fully probabilistic loss estimation formulation to evaluate the updated tail probability distribution of risk and loss. In addition, a new stochastic simulation approach is proposed to evaluate the failure probabilities with multiple performance objectives as a function of various combinations of thresholds with each threshold corresponding to one performance objective. The proposed approaches are robust to the number of random variables involved and are much more efficient than standard Monte Carlo Simulation. Although the illustrative examples mostly involve structural dynamic systems, the proposed methods developed are general enough to be applied or extended to handle problems involving other types of engineering dynamic systems and critical infrastructure systems. Theorems and mathematical proofs are also developed in this work for proving the correctness and evaluating the accuracy and computational efficiency of all the algorithms developed. Doctor of Philosophy (CEE)

In addition to static loading, reinforced concrete structures may experience various kinds of dynamic loadings such as earthquake, impact or blast. These types of dynamic loadings can lead to different loading rates on structure and result in dynamic structural response which is different from the static behavior of structure. Therefore, it is desirable to gain better understanding of the influence of loading rate on structural behavior. Nowadays, impact problems on structures have gained greater attention in structural engineering. The impact loads caused by vehicle impact, crash of aircraft, natural hazard, terrorist attack or accidental impact may cause significant damage to structures. Nevertheless, there is still no satisfactory guideline for structural design and evaluation concerning structures subjected to impact loads. Hence, research work is needed to fill the gap between the increasing engineering demand and the limited knowledge in this field. The objective of this thesis is to experimentally and analytically evaluate the behavior of reinforced concrete slabs subjected to rapid loading and low velocity impact. In this study, an experimental program was designed and carried out. In this experimental program, thirty-nine reinforced concrete slab specimens were tested in three groups. In the first group, eighteen slab specimens with six types of designs were tested under static (0.0004 m/s), medium (0.4 m/s), and high (2m/s) rate loadings to study the influences of loading rates on the behavior of reinforced concrete slab. In the second group, six slab specimens with the same types of designs as the slab specimens used in the first group were tested under low velocity impact (5.43 m/s). A comparison study between the results from the rapid loading tests in the first group and the impact tests in the second group concerning damage process, failure mode, strain rate, and energy absorption capacity was carried out to illustrate the correlation between these two types of experiments. In the third group, fifteen reinforced concrete slabs were tested under low velocity impact to study the influences of impact velocity, mass, diameter and nose shape of the impactor on the behavior of slab. From the experimental results of impact experiment, it is found that the assigned impact energy is strongly related with slab damage. Therefore, a finite element (FE) analysis is followed using LS-DYNA software to numerically study the energy capacity of reinforced concrete slabs under impact. The influences of various parameters on the energy capacity of reinforced concrete slab are evaluated. Both rapid loading and impact experiments are costly. The FE analysis also requires lots of modeling efforts and time of calculation. Therefore, simplified analytical models were proposed for obtaining the load-displacement relationship of reinforced concrete slabs under dynamic loads and predicting the response of reinforced concrete slabs under low velocity impact. The analytical load-displacement relationship is based on a quadrilinear moment-curvature relationship and the Critical Shear Crack Theory which could consider both the strength softening of slab after punching shear failure and the loading rate effect. The model for assessing the impact response of slab is a 2 degrees of freedom (2-DOF) mass-damper-spring system based on structural dynamics. This 2-DOF model is further utilized to perform a probability analysis of reinforced concrete slab subjected to low velocity impact to investigate how the slab response and damage are affected by the inherent uncertainties existed in the impact problem. Doctor of Philosophy (CEE)

The increasing demands for land space and pollution hazards incurred from old dumping grounds and landfills drive the need to employ in situ aeration technique to solve landfill aftercare problems rapidly. By injecting air into the landfill body, in situ aeration establishes aerobic condition in later stage of landfill, accelerates carbon transformation, reduces organic load, decreases landfill post-closure period and achieves earlier beneficial reuse of land. Several successful in situ aeration projects have been reported worldwide in the past decades with a variety of objectives. The efficiency of landfill aeration depends on the proper system design and operation. That is why lots of efforts have been paid on selecting the appropriate well design and spacing, the effective air distribution method, the suitable air pressure and aeration rate, and sufficient duration of aeration. However, the inception time for aeration is yet to be answered. As the waste age defines the initial landfill status before aeration, the inception time for aeration plays an essential role in the success of the aeration project. Moreover, the effects of temperature on the process of aerobic bioconversion need for clarification. This information is important to indicate if there is a need for temperature control during in situ aeration and foresee the characteristics of waste from different temperature zone in the landfill. Furthermore, no studies have been particularly cared for the microbial profiles in the course of in situ aeration. Since in situ aeration mainly relies on the local microbes to degrade the organic substances, the comprehension of microbial community and its function, especially in the incipient stage, is vital for the rapid startup and the high performance in long-term running of aeration. To address raised all above concerns, the following studies were conducted to examine the impacts of waste age and temperature on stabilization of aged waste as well as the population dynamics of microorganism at different temperature during the startup phase. In the current study, synthetically aged waste was utilized to simulate the waste composition of closed landfill or dumping ground. One reason was because the Lorong Halus Dumping Grounds (LHDG) accepted high amount of inorganic waste (> 50%) during dumping, while current waste characterization further showed that the waste ingredients were biologically inert and stabilized. Therefore waste materials from LHDG were considered unsuitable for the present study, which focused on the bioconversion process of organic matter. Another reason was ascribed to better control of the experiments, in which artificial aged wastes would minimize the influences induced by heterogeneity on the components and thus allow for more scientific comparisons. The effects of waste age on the emissions and stability of waste materials during in situ aeration were first investigated. In bioreactors with young aged waste materials, dissolved organic carbon (DOC) rapidly accumulated in the bioreactor leachate after aerobic conditions were established. Fractional analysis showed that the elevated concentration of humic acids (HAs) was primarily responsible for the increment of leachate strength. Interestingly, elevation of HAs concentration was not observed in the aeration reactor with a prolonged waste age, as the mobility of HAs was inhibited by the high molecular weight (MW) derived from extended waste age. Without significant release of organic substrate, later aeration promoted carbon biodegradation more profoundly. In sum, the beneficial properties of higher molecular weight and more stable humic substances related with later aeration are weighed up against the benefits of aerating earlier, which facilitates earlier stabilization and larger avoidance of greenhouse gas emission but also generates higher concentrations of leachable lower molecular weight compounds. The results suggest that waste age shall always be taken into account during design of aeration system, in order to maximize the aeration efficiency. The effects of temperature on carbon and nitrogen compounds during in situ aeration of aged waste were investigated by setting the operation temperature of three landfill bioreactors at 35, 45 and 55 oC, respectively. The results demonstrated that the bioreactor operated at 55 oC presented the higher carbon mineralization rate throughout the experimental period, suggesting accelerated biodegradation rates under thermophilic conditions. The leachate nitrogen speciation study indicated that organic nitrogen transcended among other species, because ammonia was significantly stripped out due to aeration. In order to elucidate the fate of individual nitrogen containing constituent, fractionation of leachate organic nitrogen was conducted. Detailed investigation revealed that the most intensive bioconversion of humic nitrogen occurred in thermophilic conditions. At the end of aeration, the waste from 55 oC bioreactor featured the highest degree of biostability and richest level of humic content. All the benefits observed in 55 oC bioreactor suggested that remediation through aeration would be more efficient if thermophilic temperature could be maintained. Moreover, thermophilic zone usually exists in the middle depth of the landfill if temperature control is not implemented. Thus, after aeration the waste from this layer could provide product with a better quality if biofertilizer and soil conditioner is the expected end use for the excavated fine particles, because thermophilic temperature could increase the yield and maturity of HAs, which is a significant factor in soil fertility. The variation of microbial community under different temperature during startup phase were assessed by comparing the 16S rRNA clone libraries derived from leachate sample of three landfill aeration bioreactors at 35, 45 and 55 oC, respectively. Compared to anaerobic control bioreactor, the microbial population under aerobic condition was more diverse as more operational taxonomic units (OTUs) were identified. In addition, the gradually established aerobic condition caused the descending of proteolytic Bacteroidetes in aerated bioreactors, while the rising in the percentage of metabolically diverse Proteobacteria with the increased temperature could partially explain why the biodegradation efficiency was increased by high temperature. Moreover, phylogenetic analyses revealed the predominant role of microaerophilic Symbiobacterium at 35 °C and obligate aerobic Vulgatibacter incomptus at 55 °C in the microbial community, verifying that a more profound aerobic condition was established at thermophilic condition most probably due to the enhanced oxygen diffusion by high temperature. Doctor of Philosophy (CEE)

The construction industry is of high economic significance and has strong environmental and social impacts, and thus sustainable construction has attracted wide attention in the industry. In order to aid in the shift towards sustainable construction, there is a need to develop a reliable model for building sustainability assessment that encompasses three dimensions of sustainability and long-term impacts and is able to facilitate sustainability-oriented decision-making. Having recognized such research need, this study developed a building-specific life cycle sustainability assessment (LCSA) model, which integrated three life-cycle based methods, namely environmental life cycle assessment (E-LCA) for environmental impact evaluation, life-cycle cost analysis (LCCA) for economic analysis and social life cycle assessment (S-LCA) for social acceptability evaluation. Firstly, a conceptual framework for LCSA model was established through extracting impact categories from three life-cycle-based methods. Economic aspect was evaluated using life-cycle costs. Environmental impact categories were extracted from a selected environmental life cycle impact assessment method, which is ReCiPe endpoint approach in this study. As for social impact assessment, impact categories were selected using stakeholder-based approach. Four groups of stakeholders were identified, including worker, occupant, local community and society. This was followed by the identification of impact subcategories through content analysis. Secondly, a building-specific social life cycle impact assessment (S-LCIA) method was proposed. Indicators were selected for each subcategory based on the assessment objective and data availability. They were categorized into three groups, including quantitative indicators in generic analysis, as well as quantitative and semi-quantitative indicators in site-specific analysis; corresponding scoring methods were also provided. Weights among impact subcategories were generated through questionnaire survey based on consistent fuzzy preference relation (CFPR) based analytic hierarchy process (AHP) method, and weights among life-cycle phases were determined considering the possibility to impose measures to control as well as level of concern of construction practitioners. Thirdly, to address the issue of uncertainty of E-LCA studies, and more specifically the uncertainty induced by input parameters, a comparative assessment on global sensitivity analysis (GSA) methods was conducted. Focusing on sampling-based GSA methods, the assessment started by comparing three sampling methods regarding convergence rate and computation effort. This was followed by the comparison of four GSA methods, whereby each method was evaluated on its capability in explaining total output variance as well as the ranking of variance contribution of individual input parameters. Accordingly, suggestions were given on characterizing uncertainties through GSA. Finally, an integrated LCSA model was established based on fuzzy ELECTRE III method. The applicability and validity of this model were demonstrated using a case study. The case study compared the sustainability performance of a modular construction project, a semi-prefabrication one and a conventional cast-in-place one. Ranking results showed that semi-prefabrication project is the best option regarding sustainability level achieved, while modular project is ranked the second. Doctor of Philosophy

Methanation of complex organic substances needs cooperation between syntrophic microorganisms. During this process, electrons and protons or other reducing equivalents are transferred from bacteria to archaea by intermediate shuttles, such as hydrogen. However, this process cannot be completed unless intermediates are readily removed. The speed of intermediates consumption is related to electron transfer efficiency between functional communities. Thus, the strategy to facilitate intermediates consumption and interspecies electron transfer could play an important role in promoting organics degradation. Direct interspecies electron transfer (DIET) is a newly discovered electron transfer process within anaerobic system, where conductive materials (CM) act as electron conduits between syntrophic partners. Theoretical calculation revealed that the electron transfer rate via DIET is substantially higher than that via interspecies molecular transfer. Therefore, DIET is beneficial to facilitate intermediates consuming rate, and remove inhibition factor such as H2 accumulation. This thesis focuses on the role and impact of CM in four application cases of anaerobic digestion (AD), i.e. thermophilic reactor start-up, toxic compounds (organic matter - phenol or inorganic matter - ammonia) degradation, and organic compounds transformation. The results exhibited CM could greatly promote methanogenic performance, enhance system stability, and improve organic compounds converting efficiency. In thermophilic AD start-up study, methane generation rate increased more than two times resulting in 50% shortened start-up time needed in CM group compared with Control group. The less affected AD performance under high hydrogen partial pressure, greater conductivity and healthy sludge morphology suggested CM trigger DIET between syntrophic partners. Similarly, one-fold higher phenol degradation rate was observed after dosing CM in a phenol degradation system. In CM groups, the electron shuttles, i.e. protein and humic substances, were greatly enriched in extracellular polymeric substances (EPS). In particular, around 2.3 to 20 folds higher protein was observed in CM group. As for organics transformation study, the addition of CM promoted 35% to 86% more methane generation. The study revealed the improved methane generation was attributed to the stimulated hydrolysis of organic matters and greater degradation of humic-like substances. Microbial community analysis showed electro-active strains, and bacteria that are capable of degrading complex organics were greatly enriched in CM groups. However, negative effects of carbon-based CM on methanogenic performance were observed in high ammonia system. This phenomenon was evidenced by a strong negative correlation between specific methane production rate and carbon nanotube (CNT) concentration (Rs = -0.972, p < 0.01). Further investigation found that potassium transportation process of the anaerobes was disturbed at the presence of CNT, and intracellular energy level was reduced probably due to the microbial detoxification activity and decreased ATP production capability. This thesis investigated the role of CM in alleviating the common obstacles of AD technology. The working principles were carefully investigated. The results indicated CM promoted organic degradation via promoting sludge conductivity, acting as electron conduit for interspecies electron transfer, enriching electron shuttles within EPS, and altering microbial community. However, the negative effects of CNT on high ammonia inhibited AD system also alerted that CM may disturb the energy transfer system and worsen inhibition on anaerobic microorganisms. This study provides a basis for future research on application of CM in AD system. Doctor of Philosophy

Strong Cold Surges (CSs) commonly occur in East Asia during the North-East Monsoon and can severely affect human life and cause considerable economic losses. We analyzed three strong CS events (CSEs) that occurred over South China during the winters of 2008, 2009 and 2016 on two broad aspects. First, a regional modelling approach that combines high resolution regional climate modeling using the Weather Research and Forecasting (WRF) model together with datasets from reanalysis, satellite, and observational weather stations is used to model the CS in South China. Second, the influence of large scale synoptic meteorology on the outbreak of CS in East Asia is investigated using data analysis of reanalysis data sets and weather charts. The WRF regional modelling approach using a two-way nesting technique reproduced the short range (hourly to daily), sudden increase in mean sea level pressure, the steep drop in surface temperature, and increased wind speed patterns during the three CSEs as observed at the Hong Kong weather station. The investigation of the large atmospheric systems over East Asia demonstrates that such CSEs originate, intensify and continue as unusually long persisting extreme cold advection due to the interaction of the three major atmospheric systems, Siberian Mongolian High, Aleutian Low and Jet Stream during the North-East Monsoon. We thus propose a new theoretical framework to explain the mechanism that leads to the development and formation of CSEs in East Asia. We propose that a CS in South China is firstly pressure-gradient driven between the Siberian-Mongolian High and the South China Sea and is further influenced by the presence of an intense low-pressure systems developed near the coast of Japan. The latter also leads to the bifurcation of the CS air mass with the low-pressure system highly influencing the CS intensity and subsequent trajectory towards the South China Sea. We also propose new criteria based on daily and monthly pressure gradient for identifying and forecasting CS at time scales varying in days (i.e. short range) to a month (extended range) over East Asia. The methodology and criteria developed are also validated against past reported events. This proposed mechanism as based on the interaction of the three large atmospheric systems has significant potential to be used as a reliable forecasting tool. Such a tool can further provide advance information to decision makers and policy makers in developing response to weather extremes. Doctor of Philosophy

Modern geotechnical systems, like any other civil engineering systems, tend to have a remarkable increase in their complexity. Also, uncertainties arise due to incomplete knowledge about the system and its environment. Addressing explicitly these uncertainties for a complex system, which may involve high nonlinearity and/or a large number of uncertain parameters, can be very challenging. Particularly, in the optimal design of deep excavations, one should take into account the sophisticated soil mechanical behaviors, the complicated soil-structure interaction, and spatial variability of soil properties. Reliability-based design optimization (RBDO) aims to model the safety-under-uncertainty aspect of design optimization by introducing reliability constraints. Among many RBDO approaches, the stochastic-sampling-based ones provide the flexibility in the choice of stochastic sampling techniques and the complexity level of numerical models. However, the required computational efforts become prohibitively large especially when expensive-to-evaluate numerical physical models are involved. In this contribution, an efficient decoupling framework for RBDO called Design Optimization in the PArtitioned Design Space (DOPADS) has been proposed. DOPADS decouples reliability constraints from the optimization loop by approximating failure probability functions (FPF) in the partitioned design space. A sufficient number of failure samples are generated using Markov chain Monte Carlo methods in each subspace, ensuring the accuracy of the approximation over the entire design space. The major gain in efficiency comes from the decoupling that explores the design space in a single reliability analysis instead of performing the reliability analyses repeatedly as in nested RBDO approaches. In the vanilla version of DOPADS, an FPF is approximated for each reliability constraint separately, which makes its computational complexity linear to the number of reliability constraints. Therefore, another framework DOPADS_m has been proposed which is tailored to the cases with multiple reliability constraints. By taking advantage of the dependency between different failure events, DOPADS_m largely enhances the efficiency of DOPADS. Design optimization is an ongoing process in which the initial design may need to be modified based on model updating using observed data. In the traditional reliability updating methods, one needs to update the distribution of model parameters in a Bayesian approach, then calculate the failure probability based on the set of the updated models. This process takes a long time which may lead to lagged decision making regarding the current reliability state. Thus, a new framework INstant REliability Updating (INREU) for reliability updating has been presented. The updated failure probability function is constructed before collecting data, making the instant plug-in query of the updated reliability possible. The application of the proposed frameworks to the deep excavation cases in Singapore has been investigated. The spatial variability of the properties of the Singapore marine clay is modeled by the random field theory. Results show that the variability of soil properties plays an important role in the design of deep excavations. Doctor of Philosophy

With the rapid increase in population density in urban cities, it is inevitable that vibrations levels due to myriad of reasons will be higher. Coupled with increased risk of terrorism, there is a need to mitigate ground vibrations caused by man-made ground shock from possible acts of terrorism. One of the most effective ways of reducing ground vibration caused by man-made activities is to introduce a seismic wave barrier between the source and the area of interest. Besides hardening an underground structure, it is possible to use a seismic wave barrier to mitigate ground shock pressure on the structure. The objective of this research is to study the responses of sand-rubber mixtures (SRM) as a seismic wave barrier to vibration and ground shock. Characterisation of SRM using laboratory tests were performed. Two separate series of small-scale field tests were performed. The first series involves using SRMs and open trench as seismic wave barrier against surface waves complemented with numerical simulations using LS-DYNA. Dimensionless amplitude ratio (Ar) contour plots were developed for use as a preliminary guide in implementation of seismic wave barrier on site. The second series involves using SRM to protect underground structure against ground shock caused by buried explosions. The field tests were modelled in LS-DYNA. The finite element model in LS-DYNA was verified to be able to correctly simulate underground explosions. The finite element model was able to replicate the field test results. In additions, the effect of density ratio between soil and structure on the peak incident pressure was examined through numerical modelling. Doctor of Philosophy

Due to competition for usable space, underground construction is an increasingly attractive option. However, the effects of a fire on the integrity and stability of underground rock structures need to be studied further to understand the potential ramification of a fire hazard within an underground rock structure. In this thesis, Brazilian tensile tests are conducted on Bukit Timah Granite specimens after exposure to different heating temperature. The variation of Brazilian tensile strength with respect to heating temperature and cooling rate of the specimens is explored and linked to the color changes of the specimens after heating. A MATLAB script is written to segmentate the specimen from the background of a photo and analyse it for its color values in the CIEL*a*b* color space. A relationship between the heating temperature and the Brazilian tensile strength of the specimens was found, as did a relationship between the color changes and the heating temperature of the specimens. The dynamic compressive strength test was also performed on both heated Bukit Timah Granite and Carrara marble specimens. An increase in heating temperature was found to reduce the dynamic compressive strength of both Carrara marble and Bukit Timah Granite, although the extent of the degradation in dynamic compressive strength is different for both materials. This is most likely due to the difference in the material of the specimens. Stress shadowing was also observed for Carrara marble. The presence of stress shadowing is influenced by the amount of energy used to compress the marble specimen as well as the heating temperature. Following this, microscopic observations of heated Bukit Timah Granite Brazilian tensile test specimens are presented. Comparisons were made between specimens that underwent a combination of heating and mechanical loading. The cumulative microcrack length, microcrack length distribution and microcrack orientation were analysed. The median microcrack length was found to similar despite the different thermal and mechanical loading. The mineralogical texture was also found to influence the length of the microcracks. Doctor of Philosophy

Portland cement (PC) is the most common binder used in concrete and construction materials. The production of PC is estimated to be at 3 billion tonnes yearly at a global scale, being responsible for 5-7% of anthropogenic CO2 emissions worldwide. Reactive magnesia (MgO) cement has received attention as an alternative binder due to the lower calcination temperatures (~700 °C) used during its production, its ability to store CO2 permanently while gaining strength, and complete recyclability at the end of use. However, the sustainable production of reactive MgO remains a challenge. Reject brine, which is a concentrated by-product with a high salt concentration obtained from treating brackish water or seawater in desalination plants, provides an ideal alternative to recover reactive MgO due to the high concentrations of Mg. This research focuses on identifying different routes to synthesize and characterize the precursors, i.e. Mg(OH)2, hydrated magnesium carbonates (HMCs) and MgC2O4•2H2O from reject brine, and to investigate the potential of the production of reactive MgO with high purity and reactivity. The relationships between the calcination conditions, e.g. calcination temperatures and durations, and reactivities of MgO have been explored. The phase change of HMCs and the carbon storage efficiency via the injection of CO2 into Mg(OH)2 slurries generated from reject brine are comprehensively studied. Finally the economic feasibility, energy consumption and carbon footprint of the production of reactive MgO from reject brine via different routes have been calculated and presented by means of life cycle assessment (LCA) Doctor of Philosophy

Mg-7Zn-5Gd-0.6Zr (wt%) alloy strengthened with quasicrystal phase (I-Mg3Zn6Gd phase) is prepared through hot extrusion and subsequent heat treatments. The low temperature (range from 25 °C to 250 °C) superplastic deformation behavior of the as-extruded, aging treated (T5) and solution and aging treated (T6) alloys are investigated. The results reveal that a superior superplastic elongation of 863% is obtained at 250 °C and strain rate of 1.67 × 10−3 s−1 and the elongation of this alloy increases with the increasing tensile temperature. Detailed microstructural analyses show that I-Mg3Zn6Gd phase and W-Mg3Gd2Zn3 phase are crushed into small particles during extrusion. A high density of nanoscale I-phase precipitates after T5 treatment. Dynamic recrystallization occurs in as-extruded Mg-7Zn-5Gd-0.6Zr alloy. The T5-treated Mg-7Zn-5Gd-0.6Zr alloy shows a relatively weak basal texture intensity, a large number fraction of high angle boundaries and a very finer grain structure (3.01 μm). During superplastic deformation, the nanoscale I-phase is slightly elongated and the microstructure is still equiaxed grains. The superplastic mechanism of the alloy is grain boundary sliding (GBS) accommodated by dislocation movement and static recrystallization. The cavity nucleation at the nanoscale I-phase/α-Mg matrix boundaries or grain boundaries and the cavity stringer formation leads to final fracture.

The casualties and economic loss in historic events have revealed that progressive collapse performance of buildings has to be evaluated in structural design to prevent such disastrous events. Integrity and resilience are important characteristics for buildings to prevent total collapse or disproportionate collapse once an unpredictable terrorism event unfortunately occurs. Compared to the extensive studies on behavior of cast-in-place reinforced concrete (RC) buildings for progressive collapse resistance, there is less research on precast concrete (PC) buildings to mitigate progressive collapse. Thus, in this study, three one-story, two-bay largescale frame-floor subassemblies (one RC and two PC) are tested under pushdown loading regime to investigate the effect of PC floor units and transverse beams on progressive collapse resilience of PC moment-resisting frames. It is found that the PC beams and slab systems could provide substantial compressive arch action and compressive membrane action, similar to the cast-in-place RC buildings. However, as PC slabs are discontinuous, insignificant tensile membrane action is able to develop in PC slab systems and the ultimate load capacity in enormous deformation stage is mainly attributed to the catenary action developed in PC beams. Published version

The emerging micropollutants have posed serious threat to the ecological environment and human beings. Among them, cytostatic drugs and antibiotics have raised great public concern due to their frequent usage, high persistence, and biological stability towards conventional water treatment processes. Therefore, this study focused on the photodegradation of cytostatic drugs and amoxicillin using UV, UV/H2O2 and UV/persulfate (S2O82-, PS) processes. In addition, quantitative structure–property relationship (QSPR) method was applied to model the photodegradation efficiency of the emerging micropollutants by UV/H2O2 and UV/PS processes. In the first part of this study, direct and indirect UV photolysis were applied to investigate the degradation effect of eight cytostatic drugs using a pseudo first-order kinetic model. Six cytostatic drugs were degraded by less than 10% at UV dose of 400 mJ·cm-2, indicating the ineffectiveness of UV photolysis towards most of the investigated cytostatic drugs. The influence of water matrix components was investigated, including natural dissolved organic matter (DOM), bicarbonate (HCO3-), nitrate (NO3-), chloride (Cl-), and sulfate (SO42-). Treated water from a water treatment plant and secondary effluent from a wastewater treatment plant were employed as natural waters to evaluate the potential application of the processes. The primary photodegradation byproducts of cytostatic drugs were identified to investigate the degradation mechanism of the processes. In the second part of this study, the reaction kinetics, degradation pathways, and antibacterial activity of UV/H2O2 and UV/PS systems were compared using amoxicillin as a typical antibiotic. The extensive use of non-metabolized amoxicillin has led to the contamination of the aquatic environment. UV irradiation alone shows negligible effect on amoxicillin degradation; while the degradation efficiency of amoxicillin increases significantly with the addition of oxidant due to the generation of radical species. The second-order rate constant of amoxicillin with HO• and SO4•- are 3.9 × 109 M-1 s-1 and 3.5 × 109 M-1 s-1, respectively. In the UV/PS system at neutral pH, the contributions of UV, HO•, and SO4•- for amoxicillin degradation are 7.3%, 22.8%, and 69.9%, respectively. Based on the experimental evidence substantiated with theoretical calculations, the degradation pathways of amoxicillin in the UV/H2O2 and UV/PS systems were proposed, including hydroxylation (+16 Da), hydrolysis (+18 Da), and decarboxylation (-44 Da). The frontier electron density of amoxicillin was calculated to predict the susceptible regions for HO• and SO4•- attack. The antibacterial activity of amoxicillin solution decreases significantly after applying UV/H2O2 or UV/PS processes. In the third part of this study, QSPR method was developed to model the second-order hydroxyl radical and sulfate radical rate constants ( and ) for a wide range of micropollutants. The modeling was conducted by a sequential process of data collection, descriptor filtration, model optimization, and model validation. 128 micropollutants were collected from the published papers and randomly divided into the training, validation, and test set. 5286 descriptors were generated from the software to develop the model. Multiple linear regression (MLR) models show low predictivity in this study. In comparison, artificial neural network (ANN) and deep neural network (DNN) models can predict the dataset accurately. Three descriptor filtration approaches were evaluated and compared, including non-dimension-reduction approach, correlation analysis approach, and principal component analysis approach. The most predictive models were validated using application domain and visualized in the Williams plot. With outliers identified and removed, the and models developed in this study show good robustness and high reliability, indicating that ANN and DNN methods can be used to evaluate the degradation of micropollutants by HO• and SO4•- in water. The selected descriptors for model indicate three reaction pathways for HO• oxidation with chemicals, namely hydrogen atom abstraction, radical addition, and electron transfer. In comparison, the electrophilic radical SO4•- tends to react with electron-rich moiety groups directly through electron-transfer mechanism. Doctor of Philosophy

Integrating multiple processes is one of the solutions for the higher requirement of modern biological nutrient removal processes. However, many challenges are also associated. This study aimed to investigate the microbial synergy and dynamics in both full-scale mixed-culture context, and lab-scale pure-culture strains. The first reported full-scale Simultaneous Nitrification-Denitrification with Phosphorus Removal (SNDPR) under tropical climate was confirmed in a local water reclamation plant through plant data analysis, batch experiment and microbial analysis. The potential contribution factors were also suggested. Considering the wide range of relative abundance in nitrifying community, Nitrosomonas europaea and Nitrobacter winogradskyi were chosen to represent pure culture ammonium oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) and cocultured in nine chemostat reactors with different initial inoculum conditions to study their abundance dynamic. Results showed that different initial AOB/NOB ratio converged to similar values after 2 ~ 4 weeks’ cultivation with AOB dominant in the full-nitrification system, indicating that operation conditions were decisive for nitrifiers’ community structure and AOB dominance was not an indication for partial-nitrification. In addition, proximity of AOB and NOB cells was observed in the coculture clusters with layered floc structure frequently appeared. The potential chemotaxis feature, which was hypothesized to contribute to the floc structure and interaction, was studied with a series of capillary assays. As an independent mechanism from the metabolic activity, the chemotaxis of AOB and NOB was studied for the first time and generated innovated research direction for biological nutrient removal. Doctor of Philosophy

Portland cement (PC) production is accountable for 5-7% of anthropogenic carbon dioxide (CO2) emissions. This has led to a growing interest in sustainable practices in line with the increased pressure on the cement and construction industries to develop alternative technologies with reduced CO2 emissions. An example of new binders developed with this goal in mind is reactive magnesia (MgO), which is produced at lower temperatures than PC (700-1000 vs. 1450 oC), and has the ability to absorb CO2 in the form of stable carbonates during accelerated CO2 curing and gain strength accordingly. The presented research incorporates two main areas involving the use of reactive magnesia within the construction industry: (i) Enhancement of carbon sequestration, mechanical performance, strain-hardening and self-healing behaviors of reactive magnesia-based and PC formulations under 10% CO2, water, air and bacterial curing, and (ii) Life cycle analysis of reactive magnesia production in comparison to PC. The first area focused on the enhancement of the carbonation process, mechanical performance, microstructural development, and strain hardening and self-healing potentials of reactive magnesia-based formulations under 10% CO2, water, air and bacterial curing, with PC formulations included as a comparison in this area. This investigation involved the evaluation of the influence of various parameters including mix design (i.e. cement, water and aggregate contents), introduction of additives (i.e. air-entrained agent (AEA), PFA and GGBS), use of alternative sources for reactive magnesia (i.e. calcined dolomite), and incorporation of fibers under 10% CO2, water, air and bacterial curing on the performance of reactive magnesia-based and PC mixes. The outcomes of this research were presented in terms of fresh and hardened properties involving the measurement of porosity, density, workability, thermal conductivity, water sorptivity, rheology, resonance frequency, crack healing efficiency, hydration and carbonation reaction mechanisms, mechanical properties and microstructural characterization of various reactive magnesia-based concrete mixes. Overall, the results indicated that introduction of AEA reduced early strength of reactive magnesia formulations due to increased air contents under 10% CO2 curing. This was compensated by increased CO2 penetration, carbonation and strength gain in longer periods. Samples in which 50% of the binder component was replaced by PFA subjected to 10% CO2 curing indicated the highest strength development, which was associated with a reduction in sample porosity due to the filler effect of PFA as well as the formation of strength providing phases through the hydration and carbonation reactions. The use of calcined dolomite was also investigated as a new source of reactive magnesia within concrete mixes. The presence of undecomposed carbonate phases in dolomite facilitated the continuation of the hydration and carbonation reactions and both reactive magnesia and calcined dolomite samples benefited from the use of high humidity (90%), whereas elevated temperatures (60 ºC) presented an advantage only in reactive magnesia samples under 10% CO2 curing. The final section of this study led to the development of reactive magnesia based strain-hardening composites (SHC) via the use of 10% CO2 curing, whose self-healing capacity was also demonstrated. The adequate binder content and w/b ratio necessary for desirable fiber dispersion was determined. The autogenous self-healing capacity of the developed binders under the presence of water and elevated CO2 concentrations was highlighted, during which the formation of hydrated magnesium carbonates (HMCs) that were capable of sealing the cracks was observed. A subsequent investigation involved the use of microbial induced carbonate precipitation (MICP), which was more effective than the use of water and CO2 in terms of crack healing efficiency in reactive magnesia-based samples, resulting in a high extent of healing products in a short time period. The second area focused on the assessment of the environmental impacts of reactive magnesia and PC production. In terms of production, reactive magnesia had a lower impact on the overall ecosystem quality and resources than PC, but posed a larger damage to human health due to the high coal usage by most plants. The research presented in this study contributed to the literature via the information generated on the relationship between the fresh and hardened properties of reactive magnesia formulations. This involved the identification of the influence of phase formations on the mechanical and microstructural development of reactive magnesia samples under 10% CO2 curing. This study is novel as it is the first in the literature to investigate the environmental impacts of the production of reactive magnesia as a binder in comparison with PC, introduce several additives (AEA, PFA and GGBS) and alternative sources for magnesium (calcined dolomite) into reactive magnesia mixes and develop reactive magnesia-based strain hardening composites via the use of accelerated CO2 curing with the ability to undergo self-healing. The reported findings have indicated the high potential of reactive magnesia-based formulations to be used in various building applications based on their ability to be produced from alternative sources and gain strength via the sequestration of CO2. Doctor of Philosophy

This study focused on localized scour formed around 45° wing-wall (WW) setback abutments in a compound channel. Fifty-five long duration scour experiments were carried out to investigate the effects of abutment length, width, degree of flow contraction on the floodplain, flow depth ratio and flow intensity (u/uc) on the time development of the geometry of scour hole and its characteristics, up to the equilibrium scour conditions. Four different water depths were tested, and different discharges were used for each water depth to achieve various flow intensities under clear water scour conditions. Seven 45° wing-wall models were used in these experiments. The experimental results showed that a secondary scour hole was formed immediately downstream the rear face of abutment models in some experiments. The longest abutment produces a secondary scour hole earlier compared to the shorter one. The narrowest model does not have a secondary hole. On the other hand, the widest model forms a secondary hole much later. The final shape of scour hole consists of a primary scour hole and a smaller secondary scour hole. The abutment width, floodplain flow depth, abutment length and flow intensity have profound effect on the formation of the secondary scour hole. The results revealed that the location of maximum scour depth generally occurs slightly downstream of the wing-wall abutment nose. The maximum scour location, Rx is affected by the flow intensity, flow depth, and abutment aspect ratio, (i.e. its length and width). This location is shifted laterally further from the abutment nose as flow intensity decreases for the same abutment aspect ratio. On the other hand. The maximum scour location Ry is only affected by flow depth, and abutment aspect ratio. However, previous studies suggested that this location is affected only by the relative abutment length. Generally, it was observed that with an increase in relative abutment length, all dimensions of scour hole and its area and volume increase. Therefore, a shorter abutment has smaller scour dimensions than the longer one. In addition, for high flow intensity, the values of these characteristics are greater than that of low flow intensity at the same value of abutment aspect ratio. The abutment width has a significant effect on the characteristics of scour hole, contrary to the findings of previous studies. Generally, with an increase in abutment width, the scour depth and width decrease. Thus, the narrower abutment has larger scour depth and width than the wider one. Conversely, the scour length, area and volume initially increase with an increase in the relative abutment width and then these characteristics reduce significantly with much wider abutment. The effect of increasing the abutment length on the scour depth and width was found to be greater than on the length of the scour hole. Moreover, the influence of decreasing the abutment width on the scour length was found to be less than on the depth and width of the scour hole. It was found that the scour width is approximately equal to 3.5 times the floodplain water depth, and this is much wider than the recommended riprap apron extension of two times the floodplain water depth suggested by previous guidelines. Equations are proposed to predict the dimension of scour hole and its area and volume. Finally, the exponential function was found to be suitable to represent the development of scour hole characteristics with time, and the proposed scour-time equations will be useful to calculate these characteristics when the flow does not last for sufficiently long time to reach its equilibrium scour conditions. Doctor of Philosophy

This thesis presents a discussion on the shear behaviour of reinforced high strength concrete beams and new proposed methods to predict the shear strength of reinforced normal and high strength concrete beams. High strength concrete is an advanced construction material with increased tensile strength and modulus of elasticity compared to normal strength concrete. Concrete structural elements with higher tensile strength for concrete material could delay the formation of the first crack and increase the cracking load. An experimental programme consisting of eleven full-scale beam specimens made of high strength concrete was conducted. The objectives of the experimental programme were: (1) to investigate the influence of effective depth on large high strength concrete beams; (2) to investigate the influence of maximum aggregate size in high strength concrete beams; (3) to study the influence of shear reinforcement ratio on size effect in high strength concrete beams; (4) to find out the minimum shear reinforcement ratio required to eliminate size effect on the shear strength, should shear reinforcement be able to do so; (5) to evaluate the efficacy of existing codes, such as ACI 318-14 (2014) and Eurocode 2 (2004), in predicting the shear strength of high strength concrete beams with varying depths; and (6) to propose new methods to predict the shear strength of large sized high strength concrete beams with and without shear reinforcement. Three parameters were studied in the eleven beam specimens to achieve the above-mentioned objectives. These three parameters were: (1) the depth of the beam specimens; (2) the maximum aggregate size; and (3) the shear reinforcement ratio. The depths of the beam specimens ranged from 450 to 1800 mm. The maximum aggregate sizes used in the concrete material varied between 10 and 20 mm. The shear reinforcement ratio provided in the two shear spans of each beam specimen was different. Four shear reinforcement ratios were provided for each beam depth (0%, 0.13%, 0.20%, and 0.30%). Shear spans with shear reinforcement ratios of 0% and 0.13% formed one beam specimen, and shear spans with shear reinforcement ratios of 0.20% and 0.30% formed another beam specimen. The shear span with lesser shear reinforcement was weaker and failed first. This failed shear span was strengthened to resume the test until failure of the other shear span. This arrangement enabled the collection of data from twenty-two shear span specimens in the eleven beam specimens. The specimens with no shear reinforcement and depths of 1350 and 1800 mm were among the largest reinforced high strength concrete beams tested to date. Together with the results of smaller specimens (with no shear reinforcement), it was shown that effective depth can influence the shear strength of high strength concrete beams in the same manner as normal strength concrete beams. The results from this study indicated that aggregate size plays a less important role in high strength concrete compared to normal strength concrete. The experimental results of the specimens with shear reinforcement showed that while shear reinforcement increases the shear strength of the specimen, it does not eliminate size effect between specimens of different depths. Yet, shear reinforcement could mitigate the influence of size effect between two specimens of different depths. The experimental results were used to evaluate the accuracy of the shear strength calculated from code equations in ACI 318-14 and Eurocode 2. Two new approaches to predict shear strength of beams with shear reinforcement were proposed. The first approach is an analytical truss method, based on softened truss model, with proposed inclusion of size effect and dowel action. These two elements were not considered in Hsu and Mo’s method (2010). Without considering size effect, the predicted shear strength from the truss model would be un-conservative for large-size concrete beams. Without considering the shear strength contribution from longitudinal reinforcement, the predicted shear strength would be very conservative for concrete beams with high amount of longitudinal reinforcement. The second approach is a simplified truss method that predicts shear strength in the form of Vn = Vc + Vs. The motivation to develop a second approach is to obtain the inclination angle of the diagonal truss similar to that obtained from the first approach, but with shorter computation procedures. Using the inclination angle of the diagonal truss, the shear strength contribution from the shear reinforcement can be obtained. In addition, an empirical equation is proposed as part of second approach to calculate the shear strength contribution from concrete, and added to the contribution from shear reinforcement to obtain the total shear strength. The novelty of the simplified truss method (second approach) is the ability to obtain both the inclination angle of the diagonal truss and shear strength of the beam without going through the iterative procedure of the first approach. The two proposed approaches were verified using the experimental results and existing published test data. The results and subsequent discussions indicated that the two approaches for predicting shear strength of a shear reinforced beam can provide reasonable accurate predictions, and at the same time is simple to apply. Keywords: high strength concrete; shear; reinforced concrete beam; size effect; shear reinforcement; aggregate size. Doctor of Philosophy

The research development of rockfill materials (RFM) was investigated by a series of large-scale triaxial tests. It is observed that confining pressure and particle breakage play important roles in the mechanical property, dilatancy relation and constitutive model of RFM. In addition, it is observed that the conventional dilatancy relation and constitutive model are not suitable for RFM due to the complex mechanical behavior. Hence, it needs to propose a unified constitutive model of RFM, considering the state-dependent and particle breakage behavior. Published version