Civil Engineering - Theses
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ItemInvestigating the benefits of considering the payload spectra of freight vehicles on pavement costs based on weigh-in-motion data( 2017)Truck traffic is a crucial factor that contributes to pavement damage. The urbanization and globalization promote the higher level of daily consumption for goods, thus increasing the derived demand for freight transport. In some countries, such as Australia, there is a trend towards using larger vehicles, which raised the road authorities’ concern about their effect on pavement because of the lack of pavement maintenance and rehabilitation funding. Therefore, it is important to have a comprehensive understanding of Australian road freight market and optimize the allocation of freight for different types of trucks to reduce the total pavement damage. Weigh-in-motion (WIM) system, which measures and records detailed vehicle information operating on road, was the data source for this study. The data was provided by the State Road Authority of Victoria (VicRoads). This thesis gave out a prototype filtering strategy for WIM database to improve the accuracy. Also, it investigated the efficiency of freight transport by comparing the effect of six-axle semi-trailers and nine-axle B-doubles with regards to pavement performance when carrying various payloads. Mathematical models were developed to help decision makers consider how to distribute the road freight task more efficiently to minimize the pavement damage induced by freight vehicles. A simplified pavement performance prediction model was utilized as a basis to determine the future pavement maintenance & rehabilitation schedules and thus, help compare the long-term pavement treatment costs for different traffic loading scenarios. The outcomes of the research showed that it would have considerable advantages in reducing the overall pavement damage by decreasing the percentage of empty trucks, changing the proportion of freight carried by B-doubles as well as optimizing the payload distributions. In addition, there would be significant benefits in the pavement maintenance & rehabilitation costs over the pavement service life by improving the allocation of freight for trucks.
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ItemHumans’ decision-making during emergency evacuations of crowded environments: behavioural analyses and econometric modelling perspectives( 2017)Modelling evacuation behaviour of humans has become an increasingly important topic due to the growth of urban populations and mass gatherings as well as the increasing frequency of emergency incidents in environments that host large numbers of humans. Emergencies are relatively rare occurrences with high potential impact and safety-related implications. Thus, preparedness for them has the potential to save lives by preventing injuries during the evacuation process and accelerating the overall process and leading people to safety in the least possible amount of time. The research on this topic ultimately aims at developing predictions tools that could facilitate evacuation planning and optimisation by producing measures such as total evacuation times for each given condition. This would enable authorities and planners to evaluate the effectiveness of their evacuation policies, identify potentially problematic locations and vulnerabilities in their venues and propose measures that can accelerate the discharge of occupants should an incidents occurs in the environment. Such applications could range from simply advising occupants as to how they should conduct themselves in case of an incident, to estimating the safe occupancy rate of venues (particularly in mass gatherings and special events) and thus managing the demand accordingly, to optimising the architectural design of the environments in ways that best support the efficient discharge of occupants. The problem is interdisciplinary by nature and has attracted the attention of researchers in various fields, including ergonomics and fire safety, applied physics and mathematics, behavioural sciences and transport engineering. The problem at hand is also highly multifaceted and entails many aspects such as computational capacities and the versatility of the models. The most crucial component of such practice is arguably the accuracy of modelling that is inextricably linked with the humans’ behaviour element and how accurately it can be replicated by the models. Given the safety-related implications of evacuation models, it is of paramount importance to minimise the extent and likelihood of inaccurate estimates that could potentially culminate in misguided designs or suboptimal policies (contradicting the primary purpose for which such models are intended). Ensuring that the behaviour of evacuees in simulated practices are replicated accurately enough is, however, a highly challenging task. The modeller deals with a problem related to humans’ decision-making behaviour which is intrinsically complex, in addition to the fact that the behaviour is this context is particularly rare and is not observed on a day to day basis. This leaves modellers with a paucity of data for model development, calibration and verification purposes. Given that the human behaviour in emergencies is not yet well understood, more often than not, the modellers have resorted to formulating “intuitive” assumptions whose accuracy have yet to be scrutinised based on empirical observations. This has left a range of mysterious theoretical assumptions in this field of research largely unverified and thus subject to debate and scepticism. I argue that the empirical knowledge in this research field has lagged notably behind the theoretical advancements and model formulations, calling for more extensive empirical research in this field in order to bridge this gap. Furthermore, by analysing the existing empirical literature in this field, I argue that the research has been distributed in a relatively imbalanced way in terms of addressing various aspects of human behaviour relevant to this research area. More empirical knowledge has been acquired in relation to the aspects of behaviour that are more convenient in terms of data collection, namely the “walking behaviour” and momentary “collision avoidance” decisions of people. Whereas, higher levels of escape decision making like the directional wayfinding choices or choices of activities are in comparison far less understood. These less explored aspects of behaviour often entail a heightened cognitive load (compared to instantaneous and largely subconscious walking decisions) and pose additional levels of complexity for experimentation, data extraction and modelling. However, I argue in that gaining an accurate understanding of these aspects and developing models that can echo them adequately in the modelling process is at least as important as modelling the walking behaviour from a practical standpoint. In this study, I focused on modelling and understanding the directional (or wayfinding) choices of humans during evacuations that are often referred to as “tactical decisions”. The study is predominantly empirical. In carrying pout this study, a major underlying question was to choose the experimentation method that best suits this problem. As explained in the literature review chapter, I classified the data collection and experimentation techniques in this field to seven major categories, a number of which could be potentially used for the question in hand here. Each method offered certain advantages and disadvantages. I study the problem using two general sources of empirical observations: hypothetical-choice data and data extracted from controlled laboratory experiments with actual crowds (which I refer to as “realistic” choice experiments or often as “field-type laboratory” experiments). The hypothetical-choice data was simply gathered by generating fixed sets of directional choice scenarios, visualising them in the form of simple pictures and surveying a sample of subjects one by one. The choice scenario conceptualise trade-offs between “social factors” and “physical factors” of the environment and elicit the prioritisation of respondents between these factors. This decision trade-off was then imitated in a more realistic simulated evacuation experiment where decision makers had to interact with actual crowds in an actual confining environment for making escape decisions. Their decisions were extracted at the level of individuals using the video-analyses of the experiment footage. The choice data obtained from both contexts were structured in an identical way and were analysed using econometric choice modelling techniques. The findings of this study are two-fold, divided into behavioural findings and econometric-related findings. The analysis results provided novel insight into the escape behaviour of humans, allowing me to revisit a number of conventional theoretical assumptions and statistically test them based on empirical observations. In particular, I examined the assumption of “herding behaviour” and “social attraction and repulsion effects” deeply entrenched in the literature. The conclusion was that these assumptions did not perfectly hold true and could in least terms be regarded as overgeneralisations of complex behavioural phenomena that could affect the accuracy of our predictions. Also the disaggregate nature of our data allowed me to address in depth the question of individual differences in this context that had largely been downplayed by previous studies. The close connection established between the hypothetical and realistic choice data also provided interesting findings about how the responses that people state as to what they would do in hypothetical escape scenarios could actually materialise when they make the actual decisions in more realistic contexts. This connection led to findings that not only did offer insight into the possible relevance of the hypothetical choice methods (or virtual-reality experiments in more general terms) in this particular context (with major implications for choosing research directions for future studies in this field) but also could be of the interest of the researchers in the field of experimental economics and econometrics. The modelling practices reported in this study were performed while considering the prospect of the outcomes leading to practical applications. I intended the models reported in this study to be implementable to evacuation simulation tools. The models, as a result, were kept parsimonious and the parameters were kept fully generic. As a practical application of this study, these models were integrated with a social-force model of walking. This dual-layer model is capable of simulating crowd evacuation process in complex environments that entail the choice of direction. Given that the parameters of the directional choice model convey behavioural interpretations, the model has also the potential to provide behavioural insight into the evacuation behaviour from a system perspective (i.e. based on aggregate measures) through computer simulation and manipulation of the simulated behaviour through varying the level of these parameters. A preliminary analysis of this kind has also been reported in the thesis.
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ItemSeismic assessment of reinforced concrete walls in Australia( 2017)Some non-ductile reinforced concrete walls in buildings were observed to perform poorly in the 2011 Christchurch earthquake, with most of the lives lost from the event caused by the collapse of buildings that relied on these structural elements for lateral support. Reinforced concrete (RC) walls are widely used throughout the Australian building stock as the primary lateral support elements. It is possible that some of these structural elements would perform poorly in a very rare earthquake due to the low standard of detailing that is currently required in Australia, as well as the low earthquake return period that the Building Code of Australia stipulates for their design. The aim of this research has been to assess the seismic performance of reinforced concrete structural walls, both rectangular and C-shaped, in Australia, a region of low-to-moderate seismicity. The current Australian Standard for Earthquake Actions, AS 1170.4:2007, stipulates earthquake hazard values that are based on a seismic hazard map that is over two decades old. A probabilistic seismic hazard analysis was conducted for most of the capital cities in Australia using the AUS5 model to provide a more accurate prediction of seismic hazard in Australia. The results indicate that for some cities, such as Melbourne, the response spectrum is expected to be higher for large return periods in comparison to the design spectra derived using AS 1170.4:2007. Furthermore, a site response study was conducted using equivalent linear analyses to investigate the amplification of the soil response as classified in AS 1170.4:2007 using a range of ground motions that would be expected in Australia. The primary conclusions from the study showed that there can be a large dependency of the soil amplification on the intensity of the earthquake ground motions for the softer soil classes. Moreover, the low intensity ground motions resulted in a higher spectral shape factor for soil class Be and Ce in comparison to factors derived from the current AS 1170.4:2007. An investigation was undertaken to find the displacement capacity of rectangular lightly reinforced and unconfined walls using a finite element modelling (FEM) program, with emphasis on finding the equivalent plastic hinge length. A Secondary Cracking Model (SCM) was formulated, which is a simple, mathematical model that has the potential to predict if a RC wall has a sufficient longitudinal reinforcement ratio to enable “secondary cracking” to occur. The SCM has been validated by comparison with results from the FEM analyses. Equivalent plastic hinge length equations were derived for the rectangular walls that were observed to form secondary cracking and a single, primary crack, and this can be used to predict the displacement capacity of these walls. This estimate of the displacement capacity assumes that the inelastic rotation that occurs over the inelastic region at the base of the wall can be modelled using an equivalent plastic hinge length over which the curvature is assumed to be a constant value. These estimates of the equivalent plastic hinge length are more appropriate for RC structural walls commonly found in Australia due to the parameters used in deriving them (e.g. mechanical properties of steel, longitudinal reinforcement ratio). Moreover, some expressions for the equivalent plastic hinge length that have derived by previous researchers were found to be inappropriate for the walls analysed in this research; these were particularly inaccurate for walls that do not have sufficient longitudinal reinforcement to force secondary cracks to form. The new expressions provide better estimates of the displacement capacity of lightly reinforced and unconfined walls when compared with recent experimental observations. One of the most widely used and popular cross-sections used in structural design of RC walls is the C-shaped section. There is a paucity of information available on the inelastic behaviour of such elements, and virtually no experimental data exists on non-rectangular concrete walls with inferior details commonly found in regions of low-to-moderate seismicity. An extensive number of nonlinear pushover analyses have been conducted based on FEM to investigate the seismic behaviour of C-shaped walls with detailing commonly found in Australia. Based on the FEM results, the SCM, that has been developed for rectangular walls, was found to be able to predict the potential of a single-crack forming in the walls. The direction of loading and mode of bending was found to be particularly important for the seismic performance of these walls. A non-ductile failure was observed for the majority of the walls investigated due to crushing of the unconfined concrete at the ends of the flanges in the governing direction of loading. Further analyses were conducted in the FEM program but with confined boundary ends to emphasise the importance of such structural detailing in allowing some plastic behaviour to be achieved for the governing direction of loading. The equivalent plastic hinge lengths derived from the extensive number of FEM analyses correlated poorly in comparison to the estimates from a number of expressions that exist in the literature, including a recently developed equation specifically for C-shaped walls. Therefore, equivalent plastic hinge lengths were derived from these results and for each direction of loading. A program has been written in MATLAB to derive vulnerability functions for low-rise, mid-rise and high-rise buildings in Australia that use structural walls as their lateral force-resisting system. The city of Melbourne was used as a template for conducting the analyses, and a dataset of thousands of buildings obtained from the National Exposure Information System (NEXIS) and Census of Land Use and Employment (CLUE) databases was included in the assessment. The displacement capacity of each of the buildings was estimated using a moment-curvature analysis followed by a plastic hinge analysis. A range of artificial earthquakes from GENQKE and real earthquakes from the PEER ground motion database on “weathered bedrock” conditions were obtained. These ground motions were subsequently used in equivalent linear analyses using the program SHAKE2000 to find the site response at the surface of different soil columns from shear wave velocity profiles taken predominantly from sites around Melbourne. The National Regolith Site Classification Map was used to estimate the soil conditions underlying each of the building sites. The acceleration and displacement response spectra resulting from these ground motions were used to represent the seismic demand for different site conditions in the capacity spectrum method and to ultimately estimate the vulnerability of the buildings. Thus, vulnerability functions were derived from the results.
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ItemBlind bolted moment connections to concrete-filled circular hollow section (CFCHS) columns for high seismic regions( 2017)When used as columns, Concrete-Filled Circular Hollow Sections (CFCHS) offer excellent strength, stiffness, and ductility in addition to an attractive appearance. There is also a construction advantage achieved by the elimination of formwork when compared with the construction of RC columns. In light of the brittle failure of welded beam to column connections experienced in the Northridge and Kobe earthquakes and the inapplicability of ordinary structural bolts when connecting beams to closed column sections, a new blind bolt which can be fixed from the outside of the CHS has been developed. This research employs ONESIDE blind bolts produced by AJAX Fasteners which have been modified to take the advantage of the concrete infill; in particular, single headed anchored blind bolts (HABBs) and double headed anchored blind bolts (DHABBs). However, although there has been considerable previous research, and there is ongoing research on moment connections to square hollow sections using the HABBs and DHABBs, there are no guidelines and clear understanding of the behaviour of moment connections to circular hollow sections using the HABBs and DHABBs. Therefore, this research initially involves both experimental and finite element work on the tensile behaviour of HABBs and DHABBs embedded in CFCHS columns, i.e. single and group behaviour. The possibility of deterioration in the behaviour when cyclic loading is applied is also investigated. Developing a semi-rigid or rigid partial-strength connection suitable for use in moment-resisting frames in regions of high seismicity is the main objective of this part of the research, with a focus on achieving sufficient strength and stiffness of the blind-bolted connection to the column. The strength hierarchy in the connection will be such that the strong and stiff blind bolted connection to the column will be paired with energy dissipating devices between this connection and the beam in a similar manner to the Sliding Hinge Joint developed previously for connections to Universal Column sections in regions of high seismicity. These devices, so-called replaceable buckling restrained fuses (RBRFs), will be automatically activated if an earthquake strikes which is larger than the design based earthquake (DBE) and they will provide sufficient displacement capacity under the maximum considered earthquake (MCE).
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ItemRoad space optimisation for multiclass and multimodal traffic networks( 2017)Traffic congestion has become a serious concern and hindrance to the prosperity of many societies. Among a variety of solutions two approaches are of significant importance: constructing new roads and bridges to ease traffic congestion and promoting public transport. For the latter, the aim is to provide more space in the heart of cities for public transport (buses, trams, etc) aiming to get more commuters to their destinations. Therefore, two central questions have been addressed in this research; (i) investment in the road construction: given a number of candidate projects associated with construction expenses and a limited budget, what is the best choice of projects. This is known as the road network design problem (NDP), and (ii) transit priority lanes: given a road network, which roads should be selected to provide a lane to be exclusively used by public transport modes such that the overall performance of the transport system is not adversely affected. This problem is called the, “transit priority lane design problem” (TPLDP). For the former, (NDP) a hybridized method consisting of the branch and bound algorithm and Benders decomposition method has been developed. For the latter (TPLDP), the concept of Braess paradox was employed to seek for “mis-utilized” space in congested networks to be utilized by public transport. To this end, a merit index aiming to spot potentially some Braess-tainted roads is introduced first. Then a branch and bound algorithm was developed to find the best subset of the Braess tainted roads that have no adverse impact on the overall performance of the network. This study advances the state of knowledge in the above mentioned problems in five areas: (i) the authenticity of the traffic model is enhanced by subjecting all the analysis to multimodal and multiclass traffic circulation, (ii) the methodologies developed in this study are tailored to real world applications as illustrated with numerical analysis, (iii) a RAM-efficient branch and bound algorithm (BB) has been developed such that the expansion of the BB’s tree structure becomes memoryless, (iv) inclusion of the Braess paradox in the pursuit of the transit priority lane would nullify possible adverse effects on the private modes, and (v) a new method for the capacitated traffic assignment has been developed which is called inflated travel time.
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ItemTowards improvement of the design of borehole ground heat exchangers( 2017)Ground source heat pump (GSHP) systems utilise ground thermal energy stored at shallow, up to 500 m, depths for heating and cooling applications. The underground elements of these systems, ground heat exchangers (GHEs), provide essential thermal interactions of the systems with the ground. In urban areas, GHEs are typically installed vertically to efficiently use the limited available land. Commonly, such GHEs comprise U-loops of plastic pipes installed in boreholes grouted with cement-based grouts after the installation of the pipes. The installation costs of borehole GHEs are usually the largest component of the capital costs of GSHP systems, so accurate sizing of borehole GHEs is crucial to provide a balance between adequate long-term performance and their financial feasibility. This research aims to contribute to the improvement of the design of borehole GHEs by advancing several aspects of current GHE design practices. Firstly, this work verifies some common borehole GHE models and modelling assumptions against experimental data. To do so, a 120kW commercial GSHP system installed in the Elizabeth Blackburn School of Sciences in Melbourne, Australia, was instrumented to monitor thermal performance of its borehole GHEs and ground-GHE thermal interactions. The system uses twenty-eight 50m deep borehole GHEs to extract and inject ground thermal energy. The GHEs and the adjacent ground were fitted with temperature probes and other instruments. The predictions made by common GHE analytical models are assessed against the 2-year monitoring data collected. This includes predictions of ground temperatures around the GHEs, estimations of borehole thermal resistances and modelling of GHE fluid temperatures. The study suggests that, in general, analytical models of borehole GHEs can be successfully used for simulations of their thermal performance, but the models have to be carefully selected for particular conditions based on their limitations. In addition, this work proposes a method for the estimation of the uncertainty of the GHE design length by considering the uncertainties involved with the selection of design parameters when a particular set of design recommendations is followed. Using the proposed method, a case study is presented where borehole GHEs are sized following a commonly applied design process. The uncertainty of the resulting length of GHEs is estimated and the sensitivity of this uncertainty to the uncertainties of individual design parameters is discussed. Also, possible measures to reduce the length uncertainty, including an in-situ thermal response test, are considered. Furthermore, this work examines the design of borehole GHEs for district hybrid GSHP (district HGSHP) systems. In such systems, two or more buildings share GHEs. This study discusses the benefits of district over individual HGSHP systems and presents a method for the optimisation of borehole GHEs for district HGSHP systems that considers thermal demand regimes of individual buildings. Such optimisation can reduce the total lifetime costs of heating and cooling, capital investments and payback periods of HGSHP systems. The importance of considering the demand regimes in the optimisation is demonstrated through a case study. The case study shows that an optimised district HGSHP system can have significant financial benefits over individual HGSHP systems.
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ItemA scenario analysis approach to distributed energy system optimisation( 2016)Distributed Energy Systems (DESs) can provide less carbon-intensive, more resilient and highly efficient alternatives to centralised electricity generation for growing urban populations. Their successful planning depends on the selection of technologies and capacities, which are heavily reliant on an unknown future energy landscape. Furthermore, precinct development, electricity and natural gas price changes, future advances in DESs efficiencies and costs and government interventions can all influence the financial performance of installations. Existing DES optimisation methods typically assess a single year of representative data and yield a single immediate investment solution without capturing or adapting for future shifts in influencing factors. Accordingly, to address the need to include these future changes, this thesis developed a framework that facilitates the selection of optimal DES investment strategies over the lifespan of a project for a range of scenarios at the precinct scale. This approach enables a more representative assessment of DES performance by considering future forecasts as well as providing the additional freedom to defer investment to later during the project life. Building energy performance simulation software (DOE 2.2) with the addition of available measured data was used in conjunction with a bottom-up archetype approach to determine precinct scale electricity and heat load profiles for an analysis period of up to 20 years. Existing hourly intermittent supply models and long-term representative meteorological years were used to estimate solar photovoltaic (PV) and small-scale wind turbine outputs. When adjoined with a combined heat and power dispatch logic formed the electricity and heat supply model. The objective of the optimisation is to minimise the net present value of costs (NPVC) associated with the supply of heat and electricity to the precinct. Optimisation decision variables pertained to investment capacity and technology for each year of assessment. Solar PV installation capacities were approximated as continuous variables and wind turbine and gas generators consisted of integer variables for type and number of units leading to a total of 80 decision variables for a 20-year assessment period. Review and testing of a variety of optimisation algorithms showed the inability of genetic algorithms (GAs) to converge within a reasonable computer run-time. An iterative hybrid approach was therefore developed where GAs were initially employed due to their ability to handle integers and global search strengths after which particle swarm optimisation (PSO) was implemented to optimise continuous variables and the process repeated. The scenario analysis approach developed was tested for the Parkville Campus, the primary precinct of The University of Melbourne between 2016 and 2036. Four scenarios were developed, capturing a range of gross floor area (GFA) growth from 11% to 65% based on the Universities strategic plan as well as future electricity and gas prices, DES investment costs and government interventions. The buildings within the Parkville Campus were categorised based on their use and construction era, resulting in a total of 16 archetypes, where each were assigned an hourly representative electricity and heat demand profile. Electricity demand was estimated based on existing measured data where average annual demand was found to vary from 95 kWh m-2 a-1 for modern office space archetypes up to 266 kWh m-2 a-1 for traditional laboratory archetypes. Heating demand was estimated using building energy simulations for hot water and space heating which were scaled to match monthly measured natural gas demand data. This resulted in modern teaching space archetypes requiring an average of 25 and 99 MJ m-2 a-1 for hot water and space heating respectively whereas traditional cafés and restaurants were found to require 201 MJ m-2 a-1 for hot water and 119 MJ m-2 a-1 for space heating. Different trial runs were conducted for each Parkville Campus scenario, (1) no DES investment, (2) the traditional optimisation approach where DES investment was ‘now or never’ or only considering a single year solution and (3) the long-term optimisation approach with DES investment was allowed at the beginning of each analysis year. Constrained optimal DES investment strategies for all scenarios selected the upper bound of 6.7 MWp of solar PV installations whilst the selection of combined heat and power (CHP) systems ranged from none to 9.3 MWp depending upon the trial case and the scenario in assessment. Scenarios with high GFA growth and the inclusion of nearby residential apartment development provided the best business case for CHP, however the long-term investment strategy recommended deferring this investment until 2022. Both the long-term approach and traditional DES investment strategies provided benefits to the university over the do-nothing approach, with different scenarios yielding: (1) a reduction of the NPVC between 3% and 18%; and (2) greenhouse gas (GHG) emission reductions between 7% and 40%. Compared to traditional optimisation approaches, it was found that the long-term scenario analysis approach resulted in greater reductions in NPVC of between 0.34% for low growth scenarios and 3.76% for high growth scenarios. This translated into a saving of between A$0.9m for low growth and A$14.6m for high growth scenarios for a twenty year NPVC of A$241.7m and A$332.7m respectively. The scenario analysis approach did not consistently yield reductions in GHG emissions compared to traditional optimisation approaches, due to the deferral of DES investment. By allowing deferral of DES investment, the long-term scenario optimisation framework was shown to have several key advantages over traditional ‘now or never’ optimisation approaches, including: reduction in upfront capital expenditure by allowing step wise investment in DES in line with projected precinct electricity and heating demand growth; provision of installation lead time for planning, approval acquisition and allocation of plant area; reduced overall NPVC particularly for high growth scenarios; lower risk of oversized DES as investments are made when required. The long-term scenario optimisation framework requires significantly more data collection and simulation than traditional approaches and is therefore only warranted where precincts are expected to undergo meaningful change over the assessment period. A more detailed heat network loss model and optimal dispatch logic algorithm would be required if this framework is to be used at the functional design stage. Finally, the inclusion of GHG emissions as a second objective and the use of multi-objective optimisation could provide decision makers with an assessment of the trade-offs between NPVC and GHG emission reduction.
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ItemDevelopment of fabric-reinforced polyurea structures for ballistic protection( 2016)Textile-reinforced structures have been increasingly applied in personal protective armours due to their blast and impact resisting capabilities. Their enhancement in energy absorption, lightweight, flexibility, and fragments capturing capabilities when subjected to ballistic impact made them the preferable alternative options to traditional metallic materials. However, the recently developed multi-laminate structures with rate-dependent and non-homogeneous materials have substantially increased the complexity in analysing the behaviour of such systems, which renders the traditional experimental-reliant development approach less capable. This research aims at establishing a new development approach for multi-material laminate structures using finite-element modelling, supported by the experimental testing of basic material properties and structural performance. A new polymer-textile laminate structure was investigated by constructing virtual composite laminate models using LS-DYNA® package. Using the third-party software commanded via the custom-developed python code, the ballistic model of the meso-scale single layer Kevlar® 29 woven fabrics was first constructed and validated to study the evolution of kinetic, strain, and frictional energy components of the fabric during the ballistic impact, as well as its damage mechanism. An improved meso-scale solid element model was then developed to resemble the Twaron® fabric properties, in order to study the influence of the woven structures and projectile impact resistance. The results have shown superior performance from the plain weave structure in comparing to other architectures. To simulate the multi-layer fabric structures, further studies using various mesh sizes have led to the development of a hybrid-mesh finite element model, which simulates the inter-yarn and inter-layer contacts of the multi-layer fabrics with enhanced computational efficiency of over 500%. The numerical models of the textile-reinforced polyurea structures were eventually constructed by combining the meso-scale hybrid-mesh Twaron® fabric model with the nonlinear polyurea model. Ballistic impact on the three-section layup structures consist of polyurea sheets and fabric piles of similar areal density was then simulated. Comparison between various multi-material structures provided insights into the criticality of the material layup arrangements. Energy absorption mechanism was compared among all structural arrangements to reveal the contribution and energy absorption capacity (EAC) of each structure.
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ItemHigh performance concrete railway sleepers( 2016)Rail transport is the safest and one of the most efficient transportation modes to move both passengers and goods. It has a range of advantages such as low travel time, high capacity, energy efficiency and low impact on the environment. The demand for rail transport is expected to keep its continuously increasing trend over the next decade. Conventional track or ballasted track is still widely used in a large number of newly established lines, even those constructed for high-speed or heavy-haul trains. Sleepers are an essential component of ballasted tracks and play a significant role in track safety and performance. While timber, steel and concrete have been used to make sleepers since the establishment of railways, nowadays, prestressed concrete sleepers (PCSs) are most commonly used as a solution to the increasing rail demand around the world. Although PCSs are a small structural element, their behaviour is very complicated due to different loading conditions, small dimensional tolerances, prestressing, steam curing, subjected to cyclic and high-magnitude dynamic loads and exposure to various environmental conditions. In addition, several reports show premature damage and early failure of PCSs that require unplanned replacement. Therefore, over the last few decades, many research projects have been aimed at identifying key behaviours, responses and interactions with other components, as well as main issues of PCSs in the track. These projects have shed some light on several aspects such as loading conditions, interactions with other components, dynamic responses and load carrying mechanisms of PCSs. The most critical problems of PCSs also have been identified globally, namely, cracking, especially from dynamic loads. However, the literature on performance of materials, particularly under dynamic loading, is still very limited. High performance concrete (HPC) is believed to be an appropriate solution to the most critical problems and unresolved issues of PCSs and is a subject of interest to the railway industry. In this regard, recently, a few research projects have been conducted to apply specific kinds of HPC as a material of PCSs in order to address their cracking or durability issues. Nevertheless, the cracking behaviour of PCSs made of HPC under dynamic loading is still lacking. Furthermore, some issues of PCSs are attributed to the inadequacy of current analysis (quasi-static) and design (permissible stress) methodology of the current standard codes of PCSs. This has motivated few researchers and organisations to shift the current design concept to a rational limit states format code. Nonetheless, establishment of a new code needs further investigation to recognise the behaviour of material under railway loads; for example, to identify the influence of dynamic loading on strength enhancement of PCS material due to strain rate effects. This study was mainly aimed at proposing the most appropriate types of HPC in order to make durable PCSs that possess sufficient resistance to cracking from high-magnitude dynamic loads. To achieve this main aim, a few specific objectives were proposed: (a) identify the level of strain rates in PCSs and their effects on material enhancement; (b) recognise the effectiveness of concrete grade on controlling PCS cracking; (c) identify the properties of concrete that effectively influence PCS cracking; and (d) identify the most appropriate types of HPC based on the findings in the previous objective. The current study was divided into five parts: (a) a comprehensive review of behaviour of PCSs; (b) an overview of specific behaviour and properties of HPC types that potentially can be suitable to make PCSs; (c) development and validation of an elaborated finite element model to simulate the behaviour of a PCS in track conditions; (d) a parametric study to investigate the influence of various factors on structural behaviour, especially cracking behaviour, of PCSs; and (e) propose the most appropriate types of HPC to produce durable PCSs. An elaborated finite element model was developed using the LS-DYNA package. The model consists of a full-scale PCS and its surrounding components. The model was calibrated using results of an experimental study, an analytical computer program, and a numerical track model. The finite element model is capable of simulating loading conditions of the track as well as all key behaviours of concrete materials under high-magnitude dynamic loads. Structural behaviour and severity of sleeper cracking were investigated using the model for a number of parameters, such as strain rate effects, concrete grade, key mechanical properties of concrete material, different levels of prestressing force, and specific combinations of these parameters. The results of this study suggest that the model developed may be used to analyse the structural behaviour of PCSs made of different materials. The effects of strain rates are recommended to be taken into consideration during the analysis and design process of PCSs. It was found that using higher grades of concrete is not an effective way to control PCS cracking from dynamic loads. The results proved that fracture energy of concrete is the most effective property of concrete to enhance the crack resistance of PCSs. It is revealed that including fibres in the concrete material is the most practical way to increase concrete fracture energy. Finally, it is recommended that using appropriate combinations of fibres and silica fume in concrete material may be the best option to make durable sleepers with adequate resistance to cracking from dynamic loads. This thesis also provides a framework to investigate the performance of different materials to make PCSs, which can be used in future studies. The thesis is expected to pave the design path to select the most appropriate types of HPC to make PCSs in various conditions and to contribute in the establishment of a new design approach.
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ItemDuctility design of very-high strength concrete columns (100 MPa-150 MPa)( 2016)Design and construction of super-tall buildings is becoming more popular around the globe due to land scarcity in metropolitan areas as a result of rapid urbanisation, as well as competition to build taller buildings. Very large loading conditions such as gravity loads, wind loads and earthquake loads are applied to tall buildings, which consequently require large member sizes. Accordingly, high strength concrete (HSC) (50–100 MPa) and very-high strength concrete (VHSC) (>100 MPa) are specified more regularly due to their higher strength, stiffness, lower deformation, and durability. Up to 150 MPa economically viable concrete can be made in-situ; however, due to its inherent brittleness and deficient guidelines on the use of VHSC, it has not been widely used around the world even though it has many desirable structural properties. Ductile design of VHSC members is paramount; however, neither existing codes of practice (ACI 318, 2011; AS 3600, 2009; NZS 3101, 2006; EC8, 2004; CSA 23.3, 2004) nor guidelines by researchers (such as Bai & Au, 2013; Kwan & Ho, 2010; and Paultre & Légeron, 2008) are able to provide ductility design guidance for compressive strengths up to 150 MPa or more. Therefore, the current codes must be reviewed, and new research is required to evaluate the suitability of VHSC and develop design guidelines for its use in order to cater for industry demands. The research program can be categorised into four major components: 1. evaluate the suitability of producing VHSC up to a compressive strength of 150 MPa or more, 2. develop theoretical expressions to predict stress-strain behaviour of VHSC, 3. develop an accurate analytical program to predict flexural behaviour of VHSC, and 4. develop guidelines for ductility design of VHSC columns. In the first component, it is concluded that self-compacting VHSC can be produced commercially up to 150 MPa or more using suitable aggregates, lower water-to-binder ratio, silica fume, and modern high-range water reducing admixtures. Suitable types of aggregates were investigated for VHSC and some feasible sources were found around Victoria, Australia. The experiments on different types of aggregates showed that mechanical behaviour and material properties of VHSC are highly dependent on types of aggregates used. In the second component, an experimental program was proposed to establish the load-displacement behaviour of confined VHSC. A novel philosophy was proposed to understand the load-displacement behaviour of confined VHSC columns, which is based on superposition of shear strength behaviour at the failure plane of concrete, confinement effects of transverse steel and dowelling action of steel. Using the above phenomenon, a new theoretical model was proposed to predict the stress-strain behaviour of VHSC columns. The third component proposed a new comprehensive and accurate analytical program to predict the full-range moment-curvature behaviour of VHSC columns, which can subsequently predict curvature ductility of columns. Also, this component evaluated the suitability of definitions of ductility indices for nominal ductility design and it proposed a new index considering the shortcomings of existing indices. Considering the fact that AS 3600 (2009) does not specify any special detailing for nominal ductility of a 50 MPa column detailed according to the minimum requirements of the code, the ductility level of a similar 50 MPa column was proposed as the ductility level for nominal ductile design. In the last component, considering the higher plastic energy stored in the VHSC columns at higher axial load levels and higher strengths, a novel philosophy was proposed for nominal ductility design of VHSC columns based on the proposed energy ductility index. Also, equations for ductility design of VHSC columns up to 150 MPa were developed based on curvature and the new energy ductility index. It can be concluded that economically feasible VHSC can be produced; and with the guidelines developed in the research project, the use of VHSC columns is feasible for structures with nominal and some moderate ductility demands.