Vipin U. Unnikrishnan

Modeling the resilience of critical infrastructure: the role of network dependencies

Abstract Water and wastewater network, electric power network, transportation network, communication network, and information technology network are among the critical infrastructure in our communities; their disruption during and after hazard events greatly affects communities’ well-being, economic security, social welfare, and public health. In addition, a disruption in one network may cause disruption to other networks and lead to their reduced functionality. This paper presents a unified theoretical methodology for the modeling of dependent/interdependent infrastructure networks and incorporates it in a six-step probabilistic procedure to assess their resilience. Both the methodology and the procedure are general, can be applied to any infrastructure network and hazard, and can model different types of dependencies between networks. As an illustration, the paper models the direct effects of seismic events on the functionality of a potable water distribution network and the cascading effects of the damage of the electric power network (EPN) on the potable water distribution network (WN). The results quantify the loss of functionality and delay in the recovery process due to dependency of the WN on the EPN. The results show the importance of capturing the dependency between networks in modeling the resilience of critical infrastructure.

Performance-Based Comparison of Different Storm Mitigation Techniques for Residential Buildings

AbstractIn recent years, severe hurricanes have caused enormous economic losses for society and placed tremendous burden on the insurance industry. As the number of residential buildings in hurricane prone regions continues to rise, hurricane hazard mitigation is of paramount importance for residential buildings. Although different retrofit measures are available to mitigate hurricane damage and to reduce the associated social and economic losses, choosing the most cost-effective ones is still an engineering challenge. This paper uses the performance-based hurricane engineering (PBHE) framework with multilayer Monte Carlo Simulation (MCS) for the loss analysis of residential buildings subject to hurricane hazard. A highly efficient modified version of the multilayer MCS technique based on copula is proposed for the faster re-evaluation of hurricane risk when different hurricane hazard mitigation strategies are considered for the same building. This technique is combined with cost-benefit analysis to provi...

Methodology for Development of Physics-Based Tsunami Fragilities

AbstractTsunamis affect coastal regions around the world, resulting in fatalities and catastrophic damage to communities. Fragility functions form the basis of most risk and resilience analyses at ...

Multihazard Interaction Effects on the Performance of Low-Rise Wood-Frame Housing in Hurricane-Prone Regions

AbstractHurricanes represent multihazard events that include wind, windborne debris, storm surge, and rainfall hazards. Conventional risk analysis does not consider the interaction between these mu...

Performance-Based Comparison of Different Design Alternatives and Retrofit Techniques for Residential Buildings Subjected to Hurricane Hazards

In recent years, severe hurricanes have caused enormous economic losses for the society and placed a tremendous burden on the insurance industry. Although different retrofit measures can be used to mitigate hurricane damage and reduce the associated social and economic losses, it is a challenge to choose the most cost effective one. In the case of residential buildings, the resources available for hurricane risk mitigation are limited and the upfront costs of improved design alternatives and retrofit measures are usually high. In this study, a probabilistic Performance-Based Hurricane Engineering (PBHE) framework is used to compare the effectiveness of different hurricane retrofit techniques for residential building from a cost-benefit point of view. A realistic case study is presented to illustrate the methodology and to evaluate the costs and benefits of different hurricane hazard mitigation techniques and design alternatives for residential buildings over the entire design life of the benchmark building.

Probabilistic framework for performance assessment of electrical power networks to tornadoes

Abstract The Electrical Power Network (EPN) constitutes a vital component of the nation’s critical infrastructure. Additionally, the resilience of the community to different natural and man-made hazards depends upon the reliability of the EPN. In this study, a probabilistic methodology is proposed for the performance assessment of EPN subject to tornadoes. The proposed methodology can be disaggregated into distinct analysis phases: hazard analysis, EPN characterization, hazard-network characterization, network analysis, and loss analysis. A hypothetical community with EPN is used to illustrate the methodology. Multi-layer Monte Carlo Simulation together with fragility functions of the components is used to calculate the probability of exceedance of the repair cost and time, to restore power to selected nodes. The methodology presented herein thus provides the ability to statistically characterize and model restoration for a given topology at a detailed enough level to be able to model dependency and potential interdependencies using mechanistic approaches.

Performance-Based Hurricane Engineering: A Multi-Hazard Approach

Hurricanes are among the most costly natural hazards affecting communities worldwide. The landfall of a hurricane involves different hazard sources (i.e., wind, wind-borne debris, flood, and rain) that interact to generate the hazard scenario for a given structure. Thus, hurricanes can be viewed and must be analyzed as multi-hazard scenarios. In this chapter, a probabilistic Performance-Based Hurricane Engineering (PBHE) framework is used for the risk assessment of a residential structure subjected to hurricane hazard. The general multilayer Monte Carlo simulation (MCS) approach is specialized for the risk assessment of pre-engineered or non-engineered buildings. A case study of a hypothetical residential house subjected to the combined hazards of wind, wind-borne debris, flood, and rainfall is considered to illustrate the sequential procedure for the probabilistic risk assessment. The results obtained from the application example include the annual probability of exceedance of repair cost for the target residential building due to each hazard and their combined effects. These results highlight the importance of considering the interaction between different hazard sources.

Probabilistic Performance Based Risk Assessment Considering the Interaction of Wind and Windborne Debris Hazard

This paper introduces a probabilistic Performance Based Hurricane Engineering (PBHE) framework for risk assessment based on the total probability theorem. This methodology disaggregates the risk assessment analysis into independent elementary components, namely hazard analysis, structural characterization, interaction analysis, structural analysis, damage analysis, and loss analysis. The proposed PBHE framework accounts for the multi-hazard nature of hurricanes. The procedure for the probabilistic risk assessment is illustrated through an application example consisting of a residential house subjected to the combined hazards of windborne debris and hurricane strong winds.

Cost-benefit assessment of different storm mitigation techniques for residential buildings using the PBHE framework

The resources available for hurricane risk mitigation of residential buildings are limited. Therefore, in order to have an optimum use of the available resources, the decision regarding the choice of mitigation/retrofit techniques for a specific project should be based on a performance-based approach. In this study, a probabilistic Performance-Based Hurricane Engineering (PBHE) framework is used to compare the effectiveness of different hurricane retrofit techniques for residential building from a costbenefit point of view. A realistic case study is presented to illustrate the methodology and to evaluate the costs and benefits of different hurricane hazard mitigation techniques for residential buildings.