Browsing by Author "Kameshwar, Sabarethinam"

Now showing 1 - 3 of 3
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    Mitigation Strategies to Protect Petrochemical Infrastructure and Nearby Communities during Storm Surge
    (ASCE, 2018) Bernier, Carl; Kameshwar, Sabarethinam; Elliott, James R.; Padgett, Jamie E.; Bedient, Philip B.
    This paper explores engineering- and social science-based strategies to mitigate risks posed by aboveground storage tanks (ASTs) during storm events. The Houston Ship Channel (HSC) is used as a case study to illustrate the application of an integrated model of built-human-natural systems and evaluate the viability of alternative risk mitigation strategies for protecting petrochemical infrastructure and nearby communities subjected to storm surge events. First, a model that couples storm surge exposure, fragility modeling, and social vulnerability of communities is used to quantify the effectiveness and economic viability of engineering-based measures to reduce spill risks, such as filling ASTs with liquid, anchoring them to the ground, changing their stiffness, or protecting them with dikes. The results indicate that no single measure is optimal and that combinations of measures could be more suitable. Thus, an optimization approach and a heuristic approach are proposed to select and combine measures considering structural and social vulnerability. Both approaches prove to be effective in reducing storm-induced spills to a given target while minimizing costs; however, they do not improve the resilience of residents in the HSC. Thus, through social science assessment of communities at risk, additional measures are identified, including improved risk communication and evacuation planning, simplified governance structures, moving from equal treatment approaches to equitable treatment approaches, and creating institutions that will empower and benefit local residents. Successful mitigation plans should cut across both engineering and social science approaches.
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    Multi-hazard Fragility, Risk, and Resilience Assessment of Select Coastal Infrastructure
    (2017-04-20) Kameshwar, Sabarethinam; Padgett, Jamie
    The performance of coastal infrastructure is threatened by natural hazards such as hurricanes and floods. The intensity and frequency of many of these climate related hazards are expected to be influenced by climate change, which will add uncertainty to the performance of coastal infrastructure. Furthermore, coastal regions are experiencing rapid population growth, which is expected to continue in the future as well. Therefore, in view of multiple hazards, uncertainty due to climate change, and increasing coastal population, comprehensive performance assessment of regional portfolio of coastal infrastructure is essential for managing the existing infrastructure and ensuring adequate performance after extreme events such as hurricanes and earthquakes. Therefore, this study focuses on the development of a methodology and supporting tools that can be used to facilitate comprehensive multi-hazard performance assessment of regional portfolios of costal infrastructure. Particularly, this study focuses on above ground storage tanks (ASTs) and bridges since they are crucial components of the energy and transportation infrastructure, respectively, and they have been observed to fail in past events with severe economic and environmental impact. First, in order to describe and effectively communicate the effects of multiple hazards on the performance and design decisions of infrastructure systems, taxonomy for multi-hazard combination is developed. For understanding the effects of different hazards on the performance and design of structures and classifying hazards according to the taxonomy this study develops a dual layer metamodel based fragility assessment methodology. The proposed method harnesses statistical learning techniques to enable efficient response and reliability assessment of structures with a broad range of design details when subjected to hazardous conditions. Using the dual layer fragility assessment methodology, fragility functions are developed for most common failure modes of ASTs: due to strong winds and storm surge. For bridges, the fragility assessment framework is used to develop fragility function for most common causes of bridge failure such as: scour, scour and vehicular loads, barge impact, barge impact and scour, hurricanes, earthquakes, and vehicle loads and earthquakes. This study also develops frameworks for ASTs and bridges to facilitate resilience assessment, i.e. their post event functionality and recovery time, which is essential for comprehensive performance assessment of ASTs and bridges. For ASTs subjected to storm surge and strong winds, the estimates of repair costs, repair time, and estimates of potential spill volumes due to tank failures are developed. Similarly, for bridges, a methodology is developed to assess the entire distribution of repair costs considering uncertainties in damage to bridge components, repair costs, and repair actions. Additionally, empirical seismic damage data is used to develop decision trees that can determine the traffic restrictions and their duration for given the damage state of bridge components such as columns, bearings, and abutments. Finally, in order to develop structure specific performance targets from regional level performance targets this study develops a simple heuristic methodology which determines the performance targets for individual structures commensurate to their performance. All the fragility and resilience assessment frameworks are applied to individual structures and regional portfolio of structures which has provided several valuable insights in to the performance of ASTs and bridges. The application of the fragility functions for ASTs for tanks in the Houston Ship Channel shows that tanks are more vulnerable to storm surges than strong winds. Additionally, application of the fragility functions show that mitigation measure such as anchoring tanks can lead to contradictory effects on the performance of ASTs for different failure modes such as flotation and buckling. For bridges, application of the fragility functions highlights that earthquakes and hurricanes can have competing effects on selection of column height. Furthermore, estimation of seismic repair costs highlights the multi-modal nature of the distribution of repair costs. The use of decision trees to determine traffic restrictions and their duration highlights the influence of damage to different bridge components on traffic restrictions. Finally, the application of the heuristic methodology to determine structure specific performance targets for all the ASTs in the Ship Channel shows that anchoring of tanks and simple procedural measures can significantly reduce the spill volumes. Similarly, application of the heuristic methodology for a portfolio of bridges in the Charleston region shows the framework can be used to obtain bridge specific performance targets which can significantly improve the performance of the entire bridge network.
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    Stiffening Ring Design for Prevention of Storm-Surge Buckling in Aboveground Storage Tanks
    (American Society of Civil Engineers, 2019) Kameshwar, Sabarethinam; Padgett, Jamie E.
    This paper proposes the use of an additional stiffening ring to prevent buckling of aboveground storage tanks (ASTs) under storm-surge inundation and presents an approach to obtain an optimal design for the additional ring. This study addresses the lack of methods to prevent storm-surge buckling of ASTs even though it has been identified as a common mode of AST failure. For this purpose, finite-element simulations were performed to study the effect of the proposed stiffening ring on the buckling response of ASTs. The critical surge height, i.e., the lowest surge height that causes AST buckling, is evaluated for a wide range of tank geometries, material properties, ring section moduli, and positions of the additional ring. The critical surge heights obtained from these simulations are used to obtain a multiparameter regression equation that can predict the critical surge height. The regression equation is further used to derive the optimal section property and the position for the additional ring as a function of tank geometry and material properties. In order to demonstrate the effect of the additional stiffening ring, the change in the critical surge height due to the installation of the additional ring is evaluated for five case-study tanks. The results show that installation of the additional stiffening ring can significantly increase the critical surge height of tanks. Furthermore, considering uncertainties from level of fill in the tank and geometric imperfections, fragility analysis for one of the case study tanks underscores the reduction in fragility, i.e.,ﾠconditional probability of buckling failure given surge level, due to the additional ring.