Journal of Structural Engineering

The concept of disaster-resilient communities has gained considerable acceptance and attention over the past decade, requiring the assessment of not only the monetary losses surrounding a hazard, but also the complex, time-dependent factors that influence community resilience. This paper presents an analytical, reliability-based approach to quantify seismic resilience based on the robustness and restoration rapidity of a portfolio of buildings following an earthquake event. The reliability problem is formulated using random variables to describe the spatially correlated seismic intensity, structural response, and duration of posthazard recovery for predefined building combinations within a portfolio. Based on these random variables, the first-order reliability method (FORM) is used as a basis to develop a new algorithm to evaluate a probability distribution of resilience for a suite of spatially distributed buildings. In addition, sensitivity measures are computed within FORM and used to prioritize cost-effective mitigation strategies to increase portfolio resilience. This assessment puts prehazard retrofit and posthazard restoration measures into a common preposterior framework to determine the most optimal allocation of resources to improve resilience given budgetary constraints. Preliminary results indicate that prehazard retrofit is often most cost-effective for increasing resilience; however, posthazard restoration efficiency is more cost-effective for achieving high resilience thresholds characterized by longer return periods.

Previous performance-based earthquake engineering investigations on highway bridges focused on repair cost and repair time metrics. These are primarily related to economic life-cycle cost analysis decision-making strategies for evaluating the vulnerability of bridges. However, environmental impacts considered during life-cycle assessment are also of interest. A methodology for quantifying the sustainability of bridge designs using carbon footprint as the performance metric is presented. Point estimates of the carbon footprint, repair cost, and repair time are used to compute resilience of several bridge-ground scenarios. Several multispan reinforced concrete highway overpass bridges in California from previous studies were selected for study because post-earthquake probabilistic repair cost and time data are already available. It is demonstrated that the disaggregation of the structure into performance groups, or components that are repaired together, and the probabilistic methodology previously employed lend themselves to the additional computations for carbon footprint. The performance groups and material quantities that drive the major contributions to carbon footprint as opposed to economic costs are presented.

Bridges play a significant role in postevent recovery and disaster resiliency of communities. Recent megadisasters, such as the 2011 Great East Japan Earthquake, have prompted the technical community to understand the robustness of infrastructure when subjected to extreme events and the shortcomings of conventional structural systems under multiple hazards. Columns are the most critical load-carrying elements of bridge structures. Enhancing the robustness of bridge columns can improve the resiliency of the bridge itself and the surrounding community by reducing repair costs and downtime after an extreme event. In recent years, the concrete-filled fiber reinforced polymer (FRP) tube (CFFT) system has been widely investigated as a durable and cost-effective alternative design for more robust bridge columns. However, the current AASHTO guide specifications are limited to nonductile, unreinforced CFFT elements. This study summarizes the findings of blast, fire, and seismic experiments performed on CFFT specimens containing minimal longitudinal reinforcement. The residual axial load-carrying capacities of damaged reinforced concrete (RC) and CFFT columns are obtained as a measure of robustness, and estimated restoration times and repair costs are presented for each type of column and each hazard. Subsequently, a set of experimentally validated design equations are developed for the axial and flexural resistance of lightly reinforced CFFT columns in a compatible format with the AASHTO load resistance factor design (LRFD) Guide Specifications for the Design of CFFTs. A formulation for displacement-based seismic design of lightly reinforced CFFT columns is presented, and a provision for the fire protection of this column system is proposed. By presenting a set of experimentally validated design formulations, this study is expected to promote the application of lightly reinforced CFFT columns to enhance the multihazard resilience of bridge infrastructure.

The concept of seismic resilience is defined as the capability of a system to maintain a level of functionality or performance in the aftermath of an earthquake event. In the research reported in this paper, a methodology for the seismic resilience assessment of existing braced-frame office buildings was developed. In this context, damage levels were defined as function of performance levels associated to earthquake intensity. Furthermore, fragility curves were derived from incremental dynamic analysis (IDA) curves obtained from time–history analyses using computer software and both aleatoric and epistemic uncertainties were considered. To illustrate the previously mentioned concept, a walkthrough of the methodology is presented in a case study comprising of existing 3-story and 6-story concentrically braced-frame (CBF) office buildings located in eastern Canada (Montreal and Quebec City) and western Canada (Vancouver). These buildings were designed in agreement with Canadian national code requirements. The proposed retrofit strategy is according to a United States standard and the retrofitted office buildings should meet the so-called basic safety rehabilitation objective class. In addition, all studied retrofitted buildings show enhanced earthquake resilience.

This paper proposes a decision-based framework to quantitatively define an indicator of structural resilience, as it pertains to mitigating blast-induced damage. The proposed procedure starts with the characterization of hazards and calculates the associated damage propagation and functional losses by deriving and subsequently balancing functional relationships between load, design, and consequences. The outcomes of each step are articulated through a series of generalized variables: (1) topology, (2) geometry, and (3) damage. Current performance-based methodologies are reviewed and adapted to provide a procedural framework that is multideterministic and accessible to engineers who rely on the current state of practice. The mathematical formulation of the proposed approach is discussed, and a design example is provided in which the proposed framework is demonstrated.

In areas of high seismicity in the United States, the design of many existing tall buildings followed guidelines that do not provide an explicit understanding of performance during major earthquakes. This paper presents an assessment of the seismic performance of existing tall buildings and strategies for increased resilience for a case study city, San Francisco, where an archetype tall building is designed based on an inventory of the existing tall building stock. A 40-story moment-resisting frame system is selected as a representative tall building. The archetype building is rectangular in plan and represents the state of design and construction practice from the mid-1970s to the mid-1980s. Nonlinear response history analysis (NLRHA) are conducted with ground motions representative of the design earthquake hazard level defined in current building codes, with explicit consideration of near-fault directivity effects. Mean transient interstory drifts and story accelerations under the 10% in 50-year ground motion hazard range from 0.19 to 1.14% and 0.15 to 0.81 g, respectively. In order to influence decision making, performance is reported as the expected consequences in terms of direct economic losses and downtime. Furthermore, to achieve increased levels of resilience, a number of strategies are proposed including seismic improvements to structural and nonstructural systems as well as mitigation measures to minimize impeding factors. Expected direct economic losses for the archetype building are in the order of 34% of building cost and downtime estimates for functional recovery are 87 weeks. The strategies presented in this paper enable up to a 92% reduction in losses and minimize downtime for functional recovery to 1 day or less.

Despite their good performance in terms of their design objectives, many modern code-prescriptive buildings built in Christchurch, New Zealand, had to be razed after the 2010–2011 Canterbury earthquakes because repairs were deemed too costly due to widespread sacrificial damage. Clearly, a more effective design paradigm is needed to create more resilient structures. Rocking, posttensioned connections with supplemental energy dissipation can contribute to damage avoidance designs (DAD). However, few have achieved all three key design objectives of damage-resistant rocking, inherent recentering ability, and repeatable, damage-free energy dissipation for all cycles, which together offer a response that is independent of loading history. Results of experimental tests are presented for a near full-scale rocking beam-column subassemblage. A matrix of test results is presented for the system under varying levels of posttensioning, with and without supplemental dampers. Importantly, this parametric study delineates each contribution to response. Practical limitations on posttensioning are identified: a minimum to ensure static structural recentering and a maximum to ensure deformability without threadbar yielding. Good agreement between a mechanistic model and experimental results over all parameters and inputs indicates the model is robust and accurate for design. The overall results indicate that it is possible to create a DAD connection where the nonlinear force-deformation response is loading history independent and repeatable over numerous loading cycles, without damage, creating the opportunity for the design and implementation of highly resilient structures.

A framework is presented for incorporating probabilistic building performance limit states in the assessment of community resilience to earthquakes. The limit states are defined on the basis of their implications to postearthquake functionality and recovery. They include damage triggering inspection, occupiable damage with loss of functionality, unoccupiable damage, irreparable damage, and collapse. Fragility curves are developed linking earthquake ground motion intensity to the probability of exceedance for each of the limit states. A characteristic recovery path is defined for each limit state on the basis of discrete functioning states, the time spent within each state, and the level of functionality associated with each state. A building recovery function is computed accounting for the uncertainty in the occurrence of each recovery path and its associated limit state. The outcome is a probabilistic assessment of recovery of functionality at the building level for a given ground motion intensity. The effects of externalities and other socioeconomic factors on building-level recovery and ways to incorporate these in the framework are discussed. A case study is presented to demonstrate the application of the proposed framework to model the postearthquake recovery of the shelter-in-place housing capacity of an inventory of residential buildings. This type of assessment can inform planning and policy decisions to manage the earthquake risk to residential housing capacity of communities.

Resilience has been defined as “the ability to prepare and plan for, absorb, recover from, and more successfully adapt to adverse events.” The term resilience is applied to a range of topics including physical security, business continuity, emergency planning, hazard mitigation, and the built environment’s (e.g., facilities, transportation systems, and utilities) ability to resist and rapidly recover from disruptive events. This paper focuses on research needs for achieving community resilience of the built environment. Community resilience depends upon the capacity of facilities and infrastructure systems to maintain acceptable levels of functionality during and after disruptive events and to recover full functionality within a specified period of time. Natural, technological, and human-made hazards in the United States continue to be responsible for significant losses and damage to the built environment. To improve the disaster resilience of communities to hazard events, each community needs to develop plans based on a risk-informed methodology that addresses multiple hazards, system performance levels, recovery of functionality, and dependencies between systems. However, quantitative tools and metrics and risk-informed guidance for communities are not presently available. A risk-informed methodology that supports decision making among alternatives for community resilience is proposed. Research needs are outlined for short-term and long-term development plans that are based on two national workshops in 2011. Research needs include risk-informed tools to support resilience planning at the community level, performance goals including functionality and recovery levels, multiple resilience levels, and standardized tools and metrics for community resilience and the built environment.

Structural control solutions can offer a decisive contribution to reducing the consequences of strong events in earthquake-affected areas, enhancing structural resilience. Furthermore, the inherent feature of some control systems, which can adapt themselves to different loading levels, can be exploited when structural conditions change due to local failures. This occurs by changing the working parameters of the control system in real time or, even if very short, over the period between two seismic events. This work deals with resilience of seismic control solutions for cable-stayed bridges through a case study represented by a standard bridge control benchmark from the literature. A strategy for recovering the optimal configuration of the controlled bridge after a damaging event is presented. Emphasis is given to the time interval between the damage occurrence and the restoration, which represent the essential aspect of the resilient behavior. Finally, the formulation of a robustness index and general procedures that suggest how to quantify resilience for the control system of cable-stayed bridges in the context of multiple hazards are explored.

For optimal functioning of societies and economies, understanding how networks of lifeline infrastructure, e.g., bridge networks, perform after a hazard is essential. Such hazard resilience can be quantified by considering the reliability of the network against disconnection or blocked network flow; however, a major challenge associated with such analysis is making sure that the component models are realistic while keeping the analysis accurate. For this reason, a methodology has been developed for realistic bridge network modeling using the following components: representative bridge classes identified by clustering a database, cutting-edge time-variant fragility models of bridges, and a multiscale network reliability analysis method, which accounts for the impact of bridge structural deterioration on network-level performance. Using the proposed methodology, the broader effects of various deterioration scenarios are investigated as well as the impacts of spatial correlation and the use of subjunctive representations of nodes in the network. The network-level relative importance of each network route is further investigated using conditional probability importance measures. Furthermore, the integrity index will be used to explore the network’s reliability and optimal strategies to improve hazard resilience.

According to NOAA, eleven billion-dollar weather disasters occurred in the United States in 2012. One of the predominant reasons that storms become disasters is the failure of civil infrastructure systems, also known as “lifelines,” on which communities rely. The approach to modeling resilience herein is through the use of systems-based models of performance. The models are based on empirical evidence of the ability of the underlying structural delivery system to provide essential infrastructure services to the community. For example, electric power delivery performance, subject to extreme storms, is sensitive to the combined system of mounted electrical and mechanical equipment, substations, and poles and towers that comprise the distribution and transmission systems. Interdependency is assessed first through previously derived input-output models of recovery to storm hazards and then significantly expanded in this paper. Further, the research results, based upon examination of extensive geocoded data for actual events, show that tropical and midlatitude cyclonic storm systems are similar in their destructive tendencies in coastal regions of the United States. These types of storms are composed of the multiple hazards of high wind speeds, precipitation, and flooding due to storm surge or heavy rainfall. Traditional analyses of infrastructure performance have relied upon evaluating the effect of one hazard or demand variable such as wind speed or peak storm surge on the loss of structural capacity. This investigation suggests that multivariate distributions of the demand variables of wind speed, storm surge, and rainfall are important for the analysis of infrastructure performance. Novel aspects of the research presented here include the synthesis of input-output interdependency models with logit transformations for system-based structural fragility relationships using multivariate hazard information, the development of multivariate hazard representations for select storms, and the use of single degree of freedom (SDOF) system analogs to model the minimization of lifeline inoperability. Another novel aspect of the research involves the extension of the inoperability SDOF model to assess correlation of the SDOF parameters with multiple weather hazard variables. Characterization of this correlation allows for the implementation of numerical simulations to predict system performance for various demand levels.

Bridge retrofitting is a common approach to enhance resilience of highway transportation systems. The study uses a multiobjective evolutionary algorithm to identify retrofit design configurations that are optimal with respect to resilience and retrofit cost. Application of this algorithm is demonstrated by retrofitting a bridge with column jackets and evaluating resilience of the retrofitted bridge under the multihazard effect of earthquake and flood-induced scour. Three different retrofit materials are used: steel, carbon fiber, and glass fiber composites. The inherent disparity in mechanical properties and associated costs of these different materials gives rise to a trade-off between cost and performance when it comes to retrofit operations. Results from the optimization, the Pareto near-optimal set, include solutions that are distinct from one another in terms of associated cost, contribution to resilience enhancement, and values of design parameters. This optimal set offers the best search results based on selected materials and design configurations for jackets.

Ensuring electric power system resilience against natural and anthropogenic hazards is vital for public health, economy, security, and well-being across modern societies. This paper presents a resilience assessment framework that focuses on computationally efficient algorithms for quantifying the response of electric power systems to hurricane events, while demonstrating its applicability to large real systems by spanning hazards, structural and system responses, and restoration processes. The study models the transmission system responses as a Bayesian network to represent probabilistic dependencies in an intuitive and tractable manner. It propagates hurricane-induced failures throughout the system to service customers while efficiently considering the physics and constraints of power flow. The framework computes customer outages in distributed $1\text{-}{\mathrm{km}}^2$ blocks connected by radial distribution feeders across the entire system, and simulates system restoration according to resource mobilization practices and a range of prioritization sequences. An illustration example using the electric power grid of Harris County, Texas, under Hurricane Ike in 2008 shows that the framework yields system responses that are in good agreement with actual outages reported after the event. It also shows that the framework requires only a fraction (2.3%) of the computation time needed by a previous outage assessment model. The example also illustrates how a resilience-informed restoration strategy can significantly improve the system-level functionality, particularly in the aftermath of hurricane events. The framework provides an efficient tool for exploring a wide range of what-if scenarios in large real systems, and supports practical use by citizens and city officials for rapid recovery and high resilience attainment.

The increased frequency of natural disasters and man-made catastrophes has caused major disruptions to critical infrastructures (CI) such as water distribution networks (WDNs). Therefore, reducing the vulnerability of the systems through physical and organizational restoration plans are the main concern for system engineers and utility managers that are responsible for the design, operation, and protection of WDNs. In this paper, a resilience index ($R$) of a WDN has been proposed that is the product of three indices: (1) the number of users temporarily without water, (2) the water level in the tank, and (3) the water quality. The resilience index is expected to help planners and engineers evaluate the functionality of a WDN, which includes: (1) delivering a certain demand of water with an acceptable level of pressure and quality, and (2) the restoration process following an extreme event. A small town in the south of Italy has been selected as a case study to show the applicability of this index using different disruptive scenarios and restoration plans. The numerical results show the importance of the partition of the network into districts to reduce the lack of services. It is also necessary to consider the indices separately to find trends that cannot be captured by the global index. Advantages and disadvantages of the different restoration plans are discussed. The proposed indices can be implemented in a decision support tool used by governmental agencies that want to include the restoration process, and the environmental and social aspects in their design procedure.

Performance assessment of a transportation network is naturally a complicated problem. This is mainly due to the fact that such a spatially distributed network is subjected to a variety of natural hazards and environmental stressors while it consists of a range of components with different ages. Among various components of a transportation network, bridges are known to be the most important but vulnerable components. Previous efforts to investigate the functionality of transportation networks, especially after earthquake events, have proven that damage to highway bridges may directly cause a major degradation in the functionality of the entire network. Considering the extensive socioeconomic consequences of network disruptions, the main focus of the current study is on the seismic resilience assessment of highway bridge networks exposed to deterioration processes. While this study provides a comprehensive computational framework to include several sources of uncertainty that must be taken into account to estimate the level of seismic risk, a special effort has been made to examine the effect of aging mechanisms on the obtained resilience measures. This new aspect provides more realistic estimates of the postevent functionality of transportation networks and can be immediately employed to identify appropriate restoration strategies.

Critical water infrastructure systems (e.g., drinking water treatment, transmission, and distribution; and wastewater and stormwater collection and treatment) are critical functions of a healthy society. Disaster resilience of these infrastructure systems during and after hazards is vital for the response and recovery to the event. Critical aspects of resiliency such as planning for hazardous conditions and taking into account interdependences with the electrical infrastructure must be understood so that water infrastructure system managers can improve system resiliency. These aspects are not always initially clear until the system is exposed to a hazard, which is why we can learn so much from recent disasters. This paper outlines and quantifies the key aspects of water infrastructure system resiliency (e.g., water system redundancy, wastewater system storage, etc.) to allow for comparison. An analysis of these parameters using historical hazardous events (i.e., hurricanes Katrina and Rita) is presented to determine what the best practices should be moving forward. Recommendations for incorporating the best practices into future designs are presented. These findings are valuable for water infrastructure system managers in need of guidance for creating a resilient system capable of handling multiple hazards.