Therese P. McAllister

Risk-Based Decision Making for Sustainable and Resilient Infrastructure Systems

AbstractThe development of infrastructure systems that are sustainable and resilient is a challenging task that involves a broad range of performance indicators over the system lifecycle that affect system functionality and recovery. Sustainability indicators address economic, social, and environmental performance metrics and resilient indicators address strength, functionality, and recovery-time metrics following a hazard event. Sustainable systems consider environmental impact and conservation of nonrenewable resources over the life of the system. Resilient systems consider performance levels relative to potential damage levels and recovery times from events. Both concepts address adequate system performance and lifecycle costs, but put a different emphasis on other indicators. Numerous sources of uncertainties associated with the lifecycle performance of infrastructure systems require the use of a risk-informed decision-making approach to properly account for uncertainties and to identify cost-effectiv...

Performance Indicators for Structural Systems and Infrastructure Networks

AbstractEstablishing consistent criteria for assessing the performance of structural systems and infrastructure networks is a critical component of communities’ efforts to optimize investment decisions for the upkeep and renewal of the built environment. Although member-level performance and reliability assessment procedures are currently well-established, it is widely recognized that a member-oriented approach does not necessarily lead to an efficient utilization of limited resources when making decisions related to the management of existing deteriorating structures or lifeline systems, especially those that may be exposed to extreme events. For this reason, researchers have renewed their interests in developing system-level assessment methods as a basis to modern structural and infrastructure performance evaluation and design processes. Specifically, system-level performance metrics and characteristics such as reliability, redundancy, robustness, resilience, and risk continue to be refined. The objecti...

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.

Behavior of Unrestrained and Restrained Bare Steel Columns Subjected to Localized Fire

AbstractReal fires start from localized burning and will not develop to flashover in an open space or in large open-plan compartments. Temperatures of gas and exposed steel columns in localized fires are not uniform. Current structural fire design methods are based on uniform heating and, therefore, do not account for temperature gradients in real fires. This paper presents a numerical investigation of the behavior of bare steel columns subjected to a localized fire. The buckling behaviors of steel columns surrounded by and adjacent to a localized fire are investigated. Simple approaches are provided to calculate the temperatures of steel columns surrounded by and adjacent to a localized fire. Sequentially coupled thermal-mechanical simulations were conducted. Unrestrained, axially restrained, and rotationally restrained steel columns of various load ratios and dimensions subjected to different heating conditions were considered. The study found that the behavior of steel columns subjected to a localized ...

Evaluation of crack growth in miter gate weldments using stochastic fracture mechanics

Many of the welded-steel miter gates found in the lock and dam system in the inland waterway system in the United States have been in service for decades and are experiencing varying degrees of degradation, primarily from fatigue and corrosion. This paper presents a finite element-based probabilistic method for assessing fatigue damage in existing miter gate structures, synthesizing several recent research developments in structural reliability for the analysis of a practical engineering problem. Analyses of miter gate structural performance revealed that the fatigue limit state often is more significant than is traditionally assumed by designers. The results of a comprehensive stochastic fatigue analysis of two gates emphasized the importance of fabrication and inspection quality control in minimizing fatigue damage in service. To support planning of inspection intervals, order statistics were used to predict the time to early fatigue failures in a structure with a number of similar weld details. This study demonstrates that stochastic fatigue analysis can be used as a practical tool for assessing the fatigue performance observed in some miter gates and for inspection and maintenance planning. It also was found that poor fatigue performance can be mitigated by modest improvements in detailing practices and inspection methods, rather than by costly changes in design practices.

Experiments and Modeling of Unprotected Structural Steel Elements Exposed to a Fire

A large-scale fire experiment was conducted to assess the accuracy of a combination of gas and solid-phase models designed to predict the temperatures of structural steel elements exposed to a fire. The experiment involved a 2 MW heptane spray fire in a compartment that was nominally 4 m by 7 m by 4 m tall. The compartment openings were designed such that natural ventilation flowed into the compartment from one side and flowed out through the opposing side. Measurements included the surface temperature of uninsulated steel elements and the temperature of the upper layer gases in the compartment. The measurements were compared to predictions made by a computational fluid dynamics model of the fire coupled with a finite-element model of the steel. The numerical predictions of the steel surface temperatures were within 8% of the measurements on-average. An analysis showed that the uncertainty in the prediction could be attributed to the uncertainty in the prescribed heat release rate in the fire model.

State of the research in community resilience: progress and challenges

Abstract Community resilience has been addressed across multiple disciplines including environmental sciences, engineering, sociology, psychology, and economics. Interest in community resilience gained momentum following several key natural and human-caused hazards in the United States and worldwide. To date, a comprehensive community resilience model that encompasses the performance of all the physical and socio-economic components from immediate impact through the recovery phase of a natural disaster has not been available. This paper summarizes a literature review of previous community resilience studies with a focus on natural hazards, which includes primarily models of individual infrastructure systems, their interdependencies, and community economic and social systems. A series of national and international initiatives aimed at community resilience are also summarized in this study. This paper suggests extensions of existing modeling methodologies aimed at developing an improved, integrated understanding of resilience that can be used by policy-makers in preparation for future events.

STRUCTURAL RESPONSE OF WTC 7 FLOOR SYSTEMS TO FIRE

The WTC 7 investigation by the National Institute of Standards and Technology (NIST) identified several factors that alone, or in combination, led to fire-induced failures of the floors, and subsequently, total collapse of the 47-story WTC 7 building. At the present time, a sensitivity study is being conducted to determine the relative contribution of the identified factors, which includes the presence or absence of shear studs on girders, connection types, asymmetric framing, and bay span lengths. The technical basis for the identified structural factors is presented in this paper.

Developing measurement science for community resilience assessment

Community resilience depends on the performance of the built environment and on supporting social, economic and public institutions which are essential for the recovery of a community following a disaster. A community’s social needs and objectives (including post-disaster recovery) are not reflected in the codes, standards and other regulatory documents that traditionally have been applied to the design and construction of individual facilities. A new approach is required, one that reflects the complex interdependencies among the physical, social, and economic systems on which a resilient and vibrant community depends. Thus, modeling the resilience of communities and cities to natural hazards depends on many disciplines, including engineering, social sciences, and information sciences. Resilience assessment has become an imperative in many countries, including the United States, Europe and the Asia-Pacific Rim. The Center for Risk-Based Community Resilience Planning, headquartered at Colorado State University in Fort Collins, Colorado and involving 10 universities and nearly 100 investigators, was established by the National Institute of Standards and Technology (NIST) in 2015. The Center’s overarching goal is to establish the measurement science needed to study and understand the factors that make a community resilient, to assess the likely impact of natural (and eventually other) hazards on communities, and to develop risk-informed decision strategies that optimize both planning for and recovery from disasters. To accomplish this goal, the Center is engaged in three major research thrusts aimed at (1) developing the Interdependent Networked Community Resilience modeling environment (IN-CORE) to assess alternative community resilience strategies quantitatively; (2) instituting a standardized data ontology, robust architecture and management tools supporting the modeling environment; and (3) performing a comprehensive set of testbeds and hindcasts to validate this advanced modeling environment. Several community resilience testbeds have been initiated during the Center’s first year. These testbeds have been designed to: (1) allow Center research teams to initiate, test, and modify essential community resilience assessment models and algorithms before the IN-CORE platform becomes fully operational; (2) stress these assessment models in a controlled manner; (3) examine varying degrees of dependency between physical, social, and economic infrastructure systems; and (4) facilitate the interdisciplinary collaborations and approaches to community resilience assessment that will be essential for the Center to achieve its ultimate goal. This special issue of Sustainable and Resilient Infrastructure is devoted to the first of these testbeds – the Centerville Virtual Community. Centerville is envisioned as a community in the Central United States that is susceptible to earthquake and tornado hazards. In most respects, it is a typical, middle-class, community of moderate size, with a median household income that is close to the national average in the United States and a diversified economy that includes commercial/retail, professional services, education/health care, industrial and government sectors. The physical infrastructure includes a variety of residential, commercial, and industrial buildings, bridges and transportation facilities, and utility networks. The physical, social, and economic systems, and

Community Resilience: The Role of the Built Environment

Buildings and infrastructure systems play a key role in communities by supporting social needs and institutions, including housing, business, government, industry, and other vital services. The concept of community resilience addresses the way that communities prepare for and recover from disruptive events. This chapter focuses on the role that buildings and infrastructure systems play in developing community resilience. The needs of citizens and institutions in a community, including public safety, define the performance requirements for buildings and infrastructure systems. However, current practice does not adequately address interdependencies between buildings and infrastructure systems or the role they play in recovery following a hazard event.