Civil & Environmental Engineering
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Item ENHANCING RESILIENCE OF COMPLEX NETWORKS: WASHINGTON D.C. URBAN RAIL TRANSIT AS A CASE STUDY(2020) Saadat, Yalda; Ayyub, Bilal BA; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)According to the United Nation’s Department of Economic and Social Affairs Population Division, 66% of the world’s population will reside in urban areas by 2050; a boost from 30 % in 1950. Urbanization has indeed triumphed and its speed has brought innovation and economic growth. Its synergies within infrastructure systems are undeniable and have increased the demand for such systems. However, urbanization is one reason infrastructure systems are knocked out of equilibrium and show complex dynamical behavior. Most infrastructure systems have been designed without planning for this magnitude of potential demographic changes; thus redesigns are long overdue. Also, climate change looms. Resource scarcity and host of other factors leave their impacts; all pose some incidence of perturbation in the state of the infrastructure system. These perturbations can affect the system’s resilience, which is a defining property of each system for remaining functional in the midst of disruption from an adverse event. Therefore, it is essential to develop appropriate metrics and methods to enhance the resilience of infrastructures at the network level. Such enhancements are critical for sustainable infrastructure development that is capable of performing satisfactorily through intentional and/or stochastic disruptions. A resilience evaluation of a network typically entails assessing vulnerability and robustness as well as identifying strategies to increasing network efficiency and performance and offering recovery strategies ideally taken in a cost-effective manner. This dissertation uses complex network theory (CNT) as the theoretic basis to enhance the resilience of large-scale infrastructure networks, such as urban rail transit systems. Urban rail transit infrastructures are heterogeneous, complex systems consisting of a large number of interacting nodes and links, which can imitate a network paradigm. Any adverse event leading to a disruption in the interaction and connectivity of network components would dramatically affect the safety and wellbeing of commuters, as well as the direct and indirect costs associated with performance loss. Therefore, enhancing their resilience is necessary. Using the Washington D.C. Urban rail transit as a case study, this dissertation develops a methodology to analyze network topology, compute its efficiency, vulnerability, and robustness in addition to provide a unified metric for assessing the network resilience. The steps of methodology are applied to two models of weighted and unweighted networks. For the weighted model two novel algorithms are proposed to capture the general pattern of ridership in the network, and to reflect the weights on assessing network efficiency, respectively. This dissertation then proposes an effective strategy to increase the network resilience prior to a disruptive event, e.g., a natural disaster, by adding several loop lines in the network for topological enhancement. As such, adding a loop line can create redundancy to the vulnerable components and improve network resilience. Expanding on this, the dissertation offers comparative recovery strategies and cost model in the case of disruption. An effective recovery strategy must demonstrate rapid optimal restoration of a disrupted system performance while minimizing recovery costs. In summary, the systematic methodology described above, assesses and enhances the network resilience. The initial results rank the most vulnerable and robust components of the network. The algorithms developed throughout the study advance the weighted network analysis state of art. The topological enhancement strategy offered basis to justify capital improvement. Post failure recovery analysis and the cost model serves to inform decision makers in identifying best recover strategies with special attention not only to restoring performance of a system but also on reducing associated failure and recovery costs. The use of the methodology proposed in this dissertation may lead to significant societal benefits by reducing the risk of catastrophic failures, providing references for mitigation of disruption due to adverse events, and offering resilience- based strategies, and related pursuits.Item RESILIENCE OF NETWORKED INFRASTRUCTURE WITH EVOLVING COMPONENT CONDITIONS: A PAVEMENT NETWORK APPLICATION(2016) Asadabadi, Ali; Miller-Hooks, Elise; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis deals with quantifying the resilience of a network of pavements. Calculations were carried out by modeling network performance under a set of possible damage-meteorological scenarios with known probability of occurrence. Resilience evaluation was performed a priori while accounting for optimal preparedness decisions and additional response actions that can be taken under each of the scenarios. Unlike the common assumption that the pre-event condition of all system components is uniform, fixed, and pristine, component condition evolution was incorporated herein. For this purpose, the health of the individual system components immediately prior to hazard event impact, under all considered scenarios, was associated with a serviceability rating. This rating was projected to reflect both natural deterioration and any intermittent improvements due to maintenance. The scheme was demonstrated for a hypothetical case study involving Laguardia Airport. Results show that resilience can be impacted by the condition of the infrastructure elements, their natural deterioration processes, and prevailing maintenance plans. The findings imply that, in general, upper bound values are reported in ordinary resilience work, and that including evolving component conditions is of value.Item STRUCTURED PROJECT FINANCE FOR PUBLIC-PRIVATE PARTNERSHIPS IN THE U.S.: AN ENHANCED APPROACH TO BETTER ACHIEVE FINANCIAL AND POLICY OBJECTIVES(2014) Farajian, Morteza; Cui, Qingbin; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As existing U.S. infrastructure ages, government entities are looking to the private sector and to alternative financing mechanisms, such as project finance, to help leverage traditional funding sources and pay for the increasing needs. As a result, the use of Public-Private Partnership (P3) delivery method in the U.S. has increased over the last two decades. The question is how the existing cases can be used to potentially enhance the current P3 model both in terms of bankability and overall procurement process maturity. This study is organized into three main parts. In the first section, project finance in general and the role of different credit enhancements in structured project finance in particular have been. In the second section, a QCA analysis has been perfumed to study and compare 18 P3 projects that have been procured in the U.S. over the last two decades. The goal is to identify logical patterns between project characteristics (i.e. capital value, term of contract, construction risk, traffic and revenue risk, and procurement competition level) and financial characteristics (i.e. equity IRR, interest rate on debt and leverage). The results are further analyzed to refine conclusions that to can provide a better understanding of how financing package of P3 projects may change based on project characteristics and policy objectives. In the third section, an enhanced P3 model has been proposed by using crowdfunding. A SWOT analysis has been conducted to explain how the proposed approach can improve current P3 model. The findings of this study can help P3 practitioners to better utilize available tools and also provides them with new tools to further enhance procurement of P3 projects. The case library provides a significant resource to practitioners as well as researchers and the proposed corwdfunding approach is a novel step toward taking P3 projects to a new maturity level.Item PROJECT PERFORMANCE BASED OPTIMAL CAPITAL STRUCTURE FOR PRIVATELY FINANCED INFRASTRUCTURE PROJECTS(2004-11-18) Sundararajan, Satheesh Kumar; Tseng, Chung-Li; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Privately Financed Infrastructure (PFI) projects are characterized by huge and irreversible investments and are faced with various risks. Project performance risks, such as project completion time and costs, affect the project value significantly, particularly in project development phase. This is because a major part of the project investments are made during this phase. Due to high uncertainties in managing the project performance risks, the selection of optimal financial structure is a challenge to Project Company sponsors and Lenders. Conventional project performance measurement and valuation methods cannot capture the dynamics of risk variables and their impact on the project value. Without such dynamic performance information, the decision of capital structure may not only be suboptimal, but lead to erroneous results. This research proposes an uncertainty evolution model, with which the dynamics of the project performance risk variables can be predicted at any desired time over the project development phase. A dynamic capital structure model is proposed, that explicitly considers the performance risks and adjusts the capital structure dynamically to counter the impact of performance risks. Numerical results show that such a model can add a significant value to a PFI project. Two risk-sharing mechanisms are also incorporated in the capital structure for a PFI project: active project management (self-support) and government support. An active project management method called {\it dynamic crashing} is proposed. By dynamically controlling the project performance through dynamic crashing, we show that the project value can be improved and the chances of potential bankruptcies can be reduced. In addition, the significance of government support as a risk-sharing mechanism is also modeled, which may be viewed as another means to protect the Project Company against the potential bankruptcies and improves the project value. Numerical results are implemented to validate the models. Overall, this research contributes an integrated framework to capital structure decisions for projects with performance uncertainties.