Civil Engineering - Theses
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ItemFurther understanding ground source heat pump system design using finite element methods and machine learning techniques( 2018)Ground-source heat pump (GSHP) systems can efficiently provide renewable energy for space heating and cooling. Even though these systems have shown great potential, contributing towards the continuously increasing energy demand and reducing greenhouse gas (GHG) emissions, our understanding of how they can be best utilised and designed can still be improved. This research adopts detailed numerical modelling and statistical approaches to provide further insights on these systems and contribute towards their worldwide adoption, focusing on three main areas. Firstly, due to the nature of their installation, there can exist disparities between the designed and installed systems. One such design-installation disparity, variable geothermal pipe separation, is addressed, aiming to reduce the gap between theory and practice. Secondly, due to the relatively recent emergence of energy geo-structures, such as energy piles or retaining walls, there currently exists little information on their utilisation/design. Therefore, an in-depth numerical analysis on energy geo-structure thermal performance is provided, focusing on the less well-researched energy retaining walls and providing suggestions on important factors such as the thermal demand, structure geometry and pipe configuration. Finally, two statistical approaches are presented that complement numerical modelling (often adopted for energy geo-structure analysis) and significantly reduce the computational time/resources associated, making numerical analysis and design of GSHP systems more accessible to engineering practice.
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ItemDesign optimisation for off-site manufacture and assembly of MEP systems( 2018)Modularisation and Standardisation for prefabrication of mechanical, electrical and plumbing (MEP) systems have become more prevalent during the last decade with the growth of the prefabricated construction industry. Speedy construction, minimum onsite labour, improved quality and waste reduction are the key benefits that make prefabrication superior to conventional construction. However, in MEP, modularisation and standardisation are currently applied only to smaller systems, where integrated packaged units are used in heating, ventilation and air conditioning (HVAC) and other building services installations. Modular prefabrication is rarely practiced when services are located within the building due to limitations during installation and difficulty in coordination. The term ‘optimum modularity’ is not accurately used in the field, and identification of modules is solely based on individual judgement than a structured method. The absence of a structured method for modularisation in MEP has made the identification of modules for prefabrication a time-consuming process, that often fails to achieve the optimum module division with minimum installation cost. In most cases, this has resulted in modular prefabrication of MEP being the same cost as conventional construction or even higher. This is one of the main reasons that impedes the use of modular prefabrication in the MEP industry. Therefore, this research has formulated an algorithm for optimum module identification in MEP systems, considering the installation cost and the functional requirements of the system. The structured modularisation process developed in the thesis, identifies the optimum module configuration to achieve minimum installation cost, while satisfying the installation and operation constraints of MEP systems. This method assists engineers and researchers to evaluate the benefits of a modular configuration compared to conventional site build strategy, prior to implementing prefabrication in MEP projects. In order to achieve these objectives, three case study project sites were visited during the construction period to identify the constraints in MEP construction and aspects to consider in the modularisation process. Chilled water central plants are chosen for the development of the modularisation algorithm, due to its complex installation process and popularity in the industry. This practical insight into the development of the method ensures that the configurations generated using the algorithm are practically constructable onsite. Structured modularisation methods practiced in various manufacturing industries such as Aerospace, Automotive, Shipbuilding and Consumer electronics were studied to identify their applicability to the construction industry. The developed structured modularisation method presented in this thesis is the only study available to date in literature, that takes an algorithmic approach to modularisation in the construction industry. An automated process of module identification, using a combination of fuzzy logic, Dependency Structure Matrix (DSM) and Hierarchical Clustering and Partitioning Algorithm (HCPA) have minimum human intervention, where input data is extracted from the Building Information Model (BIM). This leads to significant time and cost savings during the design and construction stages of MEP systems. Although the development of the algorithm was based around chilled water plant construction, the methods proposed in this thesis can be used for modularisation of other MEP central plants, such as generator, transformer and pumps, with further research on limitations and assemblies associated with a particular system. In addition to a structured method for modularisation, design engineers and researches would also require a model to evaluate the benefits of modular over conventional construction. In this regard, the output of the developed algorithm estimates the installation cost of the optimum configuration and compare the cost benefits with the conventional case, prior to implementing modular construction in MEP projects. This thesis provides a comparison of the modular approach to conventional construction, to identify a hybrid strategy to MEP plant construction. Furthermore, recommendations are provided to implement this research in other disciplines in the modular construction industry.
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ItemCollective movement of merging pedestrian crowds( 2018)Modelling pedestrian crowd movement and behaviour has emerged in the recent years in the literature as a new research topic. This topic has become important to an increasing extent due to the growth of populations of urban areas and mass events as well as an increase in the frequency of crowd-related incidents in venues that host a large number of people. Emergency incidents are considered as infrequent occurrences with safety-related ramifications and probable high effect. Although some attempts of modelling and simulating pedestrian movement have been around for decades, this field of research has recently received an apparent boost in attention in a variety of disciplines, notably in transport. The research on this subject eventually intends to develop forecasts tools that could assist in planning and optimisation for evacuation situations by providing measures including total evacuation times for each given circumstance. This would facilitate planners and authorities with the useful information required for evaluating the efficiency of their evacuation strategies in terms of time takes to vacate venues, placing potentially problematic locations and identifying weaknesses in their venues and recommend measures that can expedite the discharge of individuals should normal or emergency evacuation arise. Applications of these prediction tools could range vastly from merely guiding occupants as to in what way they should behave and manage themselves in case of occurrence of an incident, to assessing the safe density rate of venues especially in large special events and mass gatherings, too complicated optimising the design of the environments in ways that best increase the efficiency with which individuals move. The interdisciplinary problem has drawn the attention of researchers in numerous fields such as applied physics, fire safety, mathematics, ergonomics and transport engineering. The most critical element of this practice is potentially the accurateness of modelling that is inextricably linked with the behaviour of humans and extent to which their behaviour can be replicated by the proposed models. Considering implications of evacuation prediction tools and models in terms of safety, it is of major importance to reduce the possibility of imprecise estimates that could possibly culminate in inaccurate designs or misguided management policies. In order to address the challenges involved in reproducing pedestrian crowd motion, broad research has been undertaken. As stated by literature, however, most of studies has centred on understanding a class of models which we refer to as “walking-behaviour” or “next-step” models. In contrast, there has been very little knowledge as to the understanding of a higher scale of pedestrian decision making which we refer to as “route/exit” choice. Implementation of some plausible criteria which can reproduce peoples’ exit decision in an egress situation while taking into account the dynamic changes of the exit characteristics would be part and parcel of any simulated evacuation from a geometrically complex facility. I state that the experimental information in this field of research has dropped behind the mathematical progressions and model specifications. Therefore, more extensive empirical research and experimental studies in this topic are required in order to bridge this existing gap. Also, by exploring the current empirical literature, it can be concluded that the research in this field has been distributed in a comparatively unbalanced way in terms of addressing a variety of factors influencing on humans’ movements pattern. More empirical insights have been obtained related to the walking behaviour of individuals, particularly in simple experimental layouts. However, the impact of space particularly complex architectural settings on individuals’ interactions are relatively less explored. investigating this effect experimentally pose additional levels of difficulty for data collection, data extraction and drawing behavioural insights. Whereas, it is evident that acquiring a precise and comprehensive understanding of this impact and developing behavioural models that are capable of capturing this effect is of paramount importance. This research is proposed to address some of the knowledge gaps we identified with respect to the impact of space on movement dynamics of human crowds under the various level of stress. To our knowledge, the literature lacks an extensive understanding as well as robust models of the effect of geometrical features of movement area on movement pattern of individuals for egress situation. Therefore, this study primarily aims to provide an understanding of this effect particularly presence of merging corridors on egress behaviour through the provision of data obtained from a vast number of experimentations which is called for in the literature. Novel conditions and experimental layouts are to be considered as well as an advanced micro-level/ macro-level analysis are to be performed to elicit individuals’ behaviour. In addition, we analyse and present the observed interactions between occupants and their surrounding environment in a way that could be utilised for various mathematical models and simulation tools. I investigate the problem utilising two sources of experimental observations: data gained from non-human experimentation and data extracted from field-type experiments in controlled laboratory conditions with human subjects. Animal experiments data was collected by utilising panicked ants as experimental subject evacuating from various conflicting layouts. The impact of physical factors of movement environments on dynamics of the crowd was imitated in real actions where occupants were required to interact with their surrounding areas while evacuating under various levels of emergency. Their movement pattern was extracted at the level of individuals from raw footage of pedestrians. Data obtained from both sets of experiments were analysed undertaking macroscopic and microscopic measurements. While the above-mentioned problem is the primary purpose of this research, as a second question, this proposed study also intends to investigate the effect of the level of emergency on evacuees’ discharge behaviour in terms of observing “faster is slower “phenomenon. There are some merely simulated approaches as well as experimentation with non-human subjects proposed in the literature suggesting “faster is slower “ phenomenon under an emergency condition, validation of which have been primarily impeded by the scarcity of reliable explanatory data. Furthermore, to our knowledge, the impact of architectural design of egress area particularly presence of merging corridors on evacuation behaviour of the crowd has been barely examined in connection with the level of vigour to evacuate. Although the scarcity of pertinent data will still hinder us to address this problem under the extreme level of emergency situations, this study proposes some experiments under which the effect of extreme conditions is to be explored to bring to light any potential difference between the impact of space on evacuees’ behaviour under normal and emergency conditions The connection recognized between the findings obtained from experimentation with non-human organisms and humans also provided motivating insights into how the influence of the presence of conflicting layouts particularly merging corridors on the collective movement of non-human organisms is similar to that effect on the motion of human subjects. This connection led to findings that not only did offer insight into the possible relevance of collective behaviour of non-human subjects to what human occupants do in escape scenarios.
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ItemBuildings featuring irregularities in the gravity load carrying frames in low-to-moderate seismicity regions( 2018)The need of building to have column-free space at certain storeys due to architectural and aesthetical reasons, or a change in the functionality of adjacent storeys and building facility requirements, explain why many buildings feature irregularities in their gravity load carrying frames. However, discontinuities in the load-bearing system may result in unfavourable failure mechanisms under severe earthquake excitations. These buildings commonly exist in low to moderate seismic regions, like Australia; given that strict regulations do not exist with respect to earthquake resistant design of buildings. Furthermore, in these regions buildings typically have non-ductile detailing and are therefore prone to brittle and sudden failures. There is a growing need to assess the performance of vulnerable buildings in low to moderate seismic regions as it has been acknowledged that these regions are exposed to the risk of rare occurrence of devastating and damaging earthquakes. This research aims at investigating the seismic performance of a class of vertically irregular buildings in regions of low to moderate seismicity in order to provide a broad and comprehensive understanding of their response behaviour. Owing to the importance of vulnerability assessment of buildings featuring the use of transfer beams in the gravity load carrying frames (discontinuity or off-set in the load path), linear and nonlinear response behaviour of this class of buildings have been investigated thoroughly. Although “gravity frames” are assumed only to carry vertical loads, the effects of their lateral strength and stiffness need be taken into consideration in the seismic analysis. Results of studies revealed that the elastic response behaviour of vertically irregular buildings is consistent with regular buildings in terms of stiffness, modal periods, modal shapes, and lateral displacement and shear force profiles. Hence, stiffness irregularity (as a consequence of discontinuity) may not develop in the elastic range. An analysis method is known as the Generalised Force Method (GFM) which has been developed to remedy the shortcomings of the Equivalent Static Analysis method is introduced. This method is not subject to height range restrictions and is applicable to buildings that may have eccentricity, and/or transfer beam irregularity. A technique for the modelling of limited ductile beam/column components based on the concentrated plasticity modelling method has been proposed and used to develop the nonlinear models. Damage mechanism, failure patterns and weak regions of these buildings have been investigated using nonlinear analysis methods, and finally, response modification factors have been calculated for these buildings. It has been shown that a weak storey in the cases where the contributions from moment-resisting frames are high can be developed as a consequence of shear failure in the transfer beam. The behaviour of limited ductile shear walls or non-ductile columns governs the seismic behaviour of these buildings. Failure of walls due to the lack of boundary elements may occur as a result of poor detailing. However, shear failure in the transfer beams may also occur prior to the failure of walls in some cases. Hence, to avoid undesirable seismic performance behaviour such as weak storey collapse mechanism (due to the shear failure of transfer beams), more complicated methods of analysis might not necessarily result in a more desirable outcome. Ductility factors for the buildings investigated have been found to be less than 1.5. Hence, current detailing practice may not ensure a ductility value of 2.0 in compliance with AS117.4:2007, even for the regular buildings. The ductility factor for certain irregular buildings which typically has higher contributions from moment-resisting frames to the lateral stiffness have been found to be close to 1.0; which reveals the concentration of plasticity in the critical elements while elastic response behaviour is experienced with the other elements. Hence, the structure is almost entirely elastic at the onset of developing a mechanism. Guidelines and recommendations for the design of a new building in the form of designation of applicable analysis methods for these buildings and response modification factors are provided in the thesis. A straightforward method for the seismic assessment of limited ductile shear wall dominant buildings has been recommended. The method uses a rational approach to predict the nonlinear response behaviour of a given building by modifying the stiffness of individual members of an elastic model for the building structure. Moreover, a probabilistic rapid assessment tool for generating fragility curves is proposed for these buildings. This tool can be used for obtaining information for the risk assessment studies, by providing a simple and rapid method to assist global decision makers.
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ItemModelling damage to glazing and aluminium facades by flying objects( 2018)Impact by flying debris in windstorms conditions has been a major contributor to damage to aluminium, glass and other types of building facades. However, no codified design guidelines are currently available to quantify the required impact resistance of an aluminium or glazing panel for a given impact action. This research presents the development of an analytical model for assessing impact induced damage (permanent deformation or perforation) to an aluminium panel for given mass of the projectile (debris) object, velocity of impact, and importantly, parameters characterising the stiffness properties of the windborne impactor object. Stochastic methodology is developed to simulate the risk of fracture of the glass panel when subject to the transient action of point contact that can be generated by the impact of hailstones or windborne solid debris particles. The introduced simulation methodologies are able to predict the impact resistance capacity of glazing and aluminium panels without conducting impact experiments. The aim of introducing the proposed simulation model is bringing about significant savings by waiving away the need of conducting repetitive physical experimentation on panels of different dimensions, and at different rates of loading.
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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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ItemOptimisation of disaster waste management systems( 2018)The four major stages of disaster management are mitigation, preparation, response and recovery. Waste management is one of the core activities in the recovery stage and focuses on collecting, reducing or recycling, and final disposal of the remaining waste. The volume of waste generated from a single event can reach 5 to 15 times the annual waste normally produced by affected communities. The clearance, removal and disposal of such large amounts of debris are costly and time-consuming operations. However, there has been little literature dedicated to the improvement of disaster waste management (DWM) procedures compared to other operations in disaster management. The main objective of this thesis is to develop an integrated framework to improve DWM. Two sets of models that focus on two topics have been developed, namely reliability analysis of a DWM system and the two-echelon DWM system optimisation. The framework is tested for its validity and capacity for an improved understanding of the challenges in disaster waste clean-up. In the first part of the thesis, a mathematical model is built to implement the First Order Reliability Method (FORM) to investigate reliability based on variables have an impact on the system, which were identified and summarised in the literature review. An optimisation model is developed that consider the total cost and clean-up period constraints to improve reliability. To solve the optimisation model, which is non-linear, a genetic algorithm is developed. The methodology is validated using a case study in Victoria, Australia. Sensitivity analysis was conducted to identify the impact of total cost and total clean-up time on the reliability of the system. In addition, a methodology has been developed for estimating waste accumulation caused by disasters and the reliability of DWM system. These consider the uncertainty of return period and scale of disasters. To estimate the reliability of the system, FORM is used to evaluate the system's reliability. Two case studies are presented to illustrate how the methods can be applied in the real world. The reliability index curve of the system developed from sensitivity analysis can provide information for decision-makers regarding disaster waste clean-up arrangements. The approach developed can be used to analyse the effects of different parameters involved in the system after disasters. In the second part of the thesis, initially, a methodology is presented to select candidate Temporary Disaster Waste Management Sites (TDWMS) that can be regarded as a land suitability analysis problem. ArcGIS was used to conduct the analysis, which includes four main steps: identifying and determining criteria, weighting criteria, mapping standardised layers, and overlapping standardised layers. The Modelbuilder function was applied to build the analysis model. Boolean logic was used to standardise the criteria map layers. A total of 45 candidate sites were selected within the case study area in Murrindindi, Victoria, Australia. According to the analysis, the distance from groundwater, drinking water resources, and public water supplies are the most sensitive criteria. Using the location of TDWMS candidates, an optimisation model was developed for small-scale and large-scale disasters. In small-scale disasters demand from each customer node is smaller than the capacity of collection vehicles. Therefore, the problem can be seen as a Multi-Period Two-echelon Location Routing Problem (MP-2ELRP) in which the main decisions are the location of the TDWMS and the routing of vehicles in both echelons. In this thesis, both a Mixed Integer Programming (MIP) and a genetic algorithm were developed to model and solve the problem, respectively. A methodology for generating data for a case study and some alternative testing instances, which are used to evaluate the efficiency of both the model and the heuristic were developed. Computational tests indicate the robust performance of the genetic algorithm and allow for a thorough analysis of the effect of using TDWMS in terms of both the cost and the duration of the clean-up process. In large-scale disasters, the arrangement to demolish damaged buildings as well as selecting the location of TDWMS, in which the demand from each customer node is larger than the capacity of collection vehicles is considered. A multi-objective MIP model is developed that consider the limitations on the working time of vehicles, vehicle capacities and the capacity of TDWMS. The goal of the model is to minimise the total cost and total time spent in the clean-up process. Three different approaches are developed to solve the model, which are tested with artificial instances containing different numbers of customer nodes. A case study in Kinglake, Victoria, Australia, which was badly affected by the 2009 Black Saturday bush-fires, is conducted to validate the model and analyse the significance of building demolition sequences.
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ItemFlood damage assessment in urban areas( 2018)Natural disaster prevention activities are attracting greater priority since prevention is more cost-effective and less uncertain than response, and aligned with the vision and mission of sustainable development. Increasing the resilience of communities and businesses is dependent on the extension of structural and non-structural risk mitigation activities. Hence, the nation-wide frameworks of natural disaster risk management are promoting a global movement from reactive activities (response and recovery) to proactive actions (prevention and mitigation). In Australia, flood risk management is of high priority since flood is a frequent natural hazard with significant financial consequences. Flood risk assessment and flood damage estimation are the primary steps in the flood risk management process because they are essential for the identification and prioritisation of top priority areas, cost-benefit analysis, checking the feasibility of risk mitigation options, selecting best practices in risk reduction and land use planning. This research aims to develop a validated flood damage assessment framework for the geographical area of Australia using historical data collected in several disaster events to inform disaster management policy in support of the development of risk reduction measures. In Australia, due to a lack of empirical data, most damage models are not calibrated with real damage data, and few studies have been conducted on the validation of results. In addition, most approaches are absolute, which is quite rigid and does not easily transfer across time and space. All approaches are of the traditional type, which relies on a deterministic relationship between type or use of the properties at risk and the depth of water. Thus, the interaction of most damage-influencing parameters and the uncertainty of data are neglected. This study has attempted to address these issues and the knowledge gaps. Firstly, a comprehensive empirical data set including information on damage extent, flood impact variables and resistance factors was collected, and data mining, data preparation and data transformation were conducted. Since the function approach is a common and internationally accepted methodology for estimating the value of flood losses, some new relative multi-parameter flood damage assessment functions were derived, calibrated and validated for the most common residential and commercial building types in Australia. The functions were developed using the bootstrapping approach and considered the inherent uncertainty in the data sample. The performance of the new flood loss functions, in comparison to the empirical data, was contrasted with that of well-known flood damage assessment models from overseas and Australia. The new model was then transferred to a study area in Italy to check the ease of using local empirical data, evaluating the accuracy of the outcome, and assessing the ability to change parameters based on building practices across the world. Flood damage assessment is a complicated process and can be dependent on a variety of parameters which are not considered in stage-damage functions. Accordingly, a tree-based model was developed for exploring the interaction, importance and influence of other damage-influencing parameters on the extent of losses. Finally, the candidate has explored the predictive performance of the new approaches (i.e. flood loss functions and tree-based flood loss models) in assessing the extent of physical damages after temporal and spatial transfer. The predictive power of these models was tested for precision, variation and reliability, and was also checked for some sub-classes of water depth and some groups of building type. The advantages of the newly derived stage-damage functions compared to the existing Australian models include: calibration with empirical data, greater accuracy in results, a better level of transferability in time and space, consideration of the epistemic uncertainty of data, transparency of the logic behind the model and the ability to change parameters based on building practices across the world. Furthermore, results of the tree-based analysis showed that while water depth is the most significant damage predictor in the area of study, floor space, private precautionary measures, building value and building quality also correlate with the extent of flood losses. Also, the tree-based models are shown to be more accurate than the stage-damage function. Thus, considering more parameters and taking advantage of tree-based models are recommended. Finally, it has been shown that considering more details of the damaging process can be useful for enhancing the level of transferability of damage models in time and/or space. Overall, this thesis presents a significant contribution to the flood damage assessment process by offering a calibrated and validated flood loss estimation framework. The results provide the input data for subsequent damage reduction, vulnerability mitigation and disaster risk reduction.
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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.