Post-Extreme Event Damage Assessment and Response for Highway Bridges (2016)

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3 for the rapid assessment of their structural conditions and plan to address the possible consequences of failures. One of the major issues hindering such technologies is the variability of the types of hazards that structures are exposed to throughout the United States. Large portions of the United States are vul- nerable to the natural hazards of geologic origin (e.g., earth- quakes and tsunamis) or of hydro-meteorological origin (e.g., hurricanes and floods). This is in addition to the possibility of the occurrence of man-made hazards with intentional sources (e.g., terrorist attacks) or accidental sources (e.g., vehicle and vessel collisions) (Alipour et al. 2013b). Furthermore, in addition to natural and man-made hazards, the transportation infrastruc- ture is exposed to harsh environmental stressors, which may significantly affect the durability of structural components. To investigate each of these discussed aspects, following the completion of the planned survey and literature review, this project will look into the region-specific hazards and their potential effects on the choices made by the responsible authorities for the integrity assessment of highway bridges. DEFINITION OF EXTREME EVENTS The definition, classification, and diagnosis of extreme events are complex. There is no universal unique definition of an extreme event. From a mathematical standpoint, to define an extreme event would require a statistical or an historical distribution. Extreme values based on observational data are important in safety and life-cycle assessment of structures. The prediction of future conditions, especially extreme conditions, is necessary in bridge design and is performed based on an extrapolation from previously observed data combined with engineering judgement. Bier et al. (1999) defined “extreme events” as being extreme in terms of both their low frequency and high severity. Ghosn et al. (2003) defined extreme events as man-made or environmental hazards having a high poten- tial for producing structural damage that are associated with a relatively low rate of occurrence. AASHTO–LRFD (Load and Resistance Factor Design) introduced “Extreme Event Limit States” to evaluate the performance of bridges during earthquakes, scour, or other hydraulic events; ice loads; or ship collisions, but does not necessarily provide clear defi- nitions of extreme events. The LRFD specification adopted a limit state philosophy or state beyond which a component ceases to satisfy the provisions for which it was designed. The idea of the limit state provides a systematic approach to ensuring the satisfactory short- and long-term performance of The U.S. highway transportation network contains more than 650,000 bridges, which are essential to maintaining the net- work performance. The existing bridges are, however, vulner- able to a variety of natural and man-made hazards and may act as bottlenecks in the event of any failures. The most com- mon extreme events include natural hazards such as ground excitation during earthquakes, high wind and storm surge in hurricanes, and scouring and debris impacts during floods. The vulnerability of bridges under such extreme events can be best understood by considering that the average age of theses bridges is 45 years. Furthermore, with truck miles nearly dou- bling over the past 20 years and many trucks carrying heavier loads, an excessively increased traffic load and subsequent rapid deterioration is expected for most bridges (ASCE 2013); this is in addition to increased risks resulting from regular truck overloads. Despite several advances in the available technolo- gies for the design of new bridges and the retrofit of the exist- ing ones, there are still incidents where bridges fail partially or completely after an extreme event. In such cases, it is important for the federal, state, and local authorities to identify the dam- aged bridges, quantify the extent of the damage, implement a plan for rapid recovery, and provide alternative routes for emer- gency response and evacuation activities. For this purpose, NCHRP Synthesis Topic 46-11 has gathered relevant infor- mation on the technologies available for rapid post-extreme event damage assessment of highway bridges, the availability of these data to transportation agencies and bridge owners, decision-making tools or processes that would use the data, and the emergency planning protocols in place to address the failures in bridges. The performance assessment of aging transportation infra- structure under extreme events has long been an issue of con- cern for engineers and decision makers who are involved with the operation and management of civil infrastructure systems. A major aspect of transportation systems that makes it differ- ent from the other constructed facilities is the spatial distribu- tion and connectivity of infrastructure components. This has made the transportation systems more sensitive to the conse- quences of natural and man-made hazards, as disruptions in only a few components may result in detrimental effects on the performance of the entire system. Furthermore, at a larger scale, any damage to infrastructure components may cause extensive socioeconomic losses, some of which cannot even be properly measured. To minimize the extent of the disrup- tion in the performance of the highway bridge infrastructure, it is of paramount importance to develop new technologies chapter one INTRODUCTION

4 bridges (Lee et al. 2008). Alipour et al. (2013a) defined extreme events as those large intensity events with lower probability of occurrence that could push the structure beyond its expected response (i.e., the response that the engineer has designed the structure for). Following that definition, a holistic definition of an extreme event requires: • Objective and unambiguous identification of the event, • Definition of the intensity of the event as a function of its features and the risk that it generates for the built environment, and • Definition of an intensity-frequency probability density function that represents the statistics of the event occur- rence for each class of intensity. Here it is believed that for a more holistic definition of the extreme event three main factors could be considered: • The definition of the extreme event is a function of space and time: (1) events that are extreme in one area of the world may not be in another and (2) events that are extremes at one time may not be so in the future or the past. For instance, a specific earthquake intensity that is considered extreme in the state of Virginia may not be an extreme event in the state of California, simply because such events have been considered in the design of bridges in the latter. In addition, after the Loma Prieta and Northridge earthquakes major revisions were made to the seismic bridge design provisions such that future events with similar intensities may result in lower fail- ures in the region. • It is important that the characterization of an extreme event take into account the spatial scale and temporal scale of the event in addition to its intensity. For instance, a river flooding may result in erosion of the foundations of many of the bridges downstream that would require full or partial closure until full inspections and repairs are conducted. This translates into a regional disruption with large spatial impact that could adversely affect the everyday life and economy of the regions depending on those bridges. This is in contrast with the extent of dis- ruption created by an over-height truck collision. In the latter case, only the traffic over the bridge and possibly the road underneath would be hindered, making it an isolated event (AuYeung and Alipour 2016). • The definition of an extreme event is a function of its consequences and the impacts that it has on the safety of the human and the built environment (here transportation assets). For example, an event (even isolated) that could damage a critical bridge in a transportation network can have major consequences on the performance of the system and as such be categorized as extreme. A good example is the failure of the Skagit Bridge in Seattle, Washington, that resulted in long detours and thousands of hours of traffic delays (refer to example practices in Washington State); in this case, the event, although iso- lated, resulted in lasting effects in the regional transpor- tation network, making it an extreme event. TRANSPORTATION INFRASTRUCTURE RESILIENCE IN THE FACE OF EXTREME EVENTS The concept of resilience can be applied to systems such as buildings, bridges, facilities, infrastructure, networks, econom- ics, and communities. The general concept of resilience was first put forth by ecologists more than 40 years ago. According to Holling (1973), resilience is the perturbation that can be absorbed before the system converges to another state of equi- librium. Resilience was redefined by Primm (1984) as a speed measure for engineering systems to return to the equilibrium condition. In another study, the intrinsic ability of a system to adjust its functioning before, during, or after changes and dis- turbances so that it can sustain required operations under both expected and unexpected conditions is considered resilience (Hollnagel et al. 2011). Bruneau et al. (2003) also conducted a comprehensive analysis of various aspects of resilience at the community level and suggested that it had four dimensions, called the four “Rs”: robustness, redundancy, rapidity, and resourcefulness. Here, robustness is the ability of the system or components of the system to withstand external shocks without significant loss of performance. Redundancy is the extent to which the system satisfies and sustains functional requirements in the event of disturbance. Resourcefulness is the ability to diagnose and prioritize problems and to initiate solutions by identifying and monitoring all resources, includ- ing economic, technical, and social information. Rapidity is the speed at which recovery is accomplished. According to this definition, implementation of the resilience can enhance the performance of the system by reducing the probability of fail- ure, consequences of failure, and time to recovery. A holis- tic definition of resilient governance for communities was provided by Godschalk et al. (2009); resilient communities proactively protect themselves against hazards, build self- sufficiency, and become more sustainable instead of sus- taining repeated damage and continual demands for federal disaster reliefs. The National Academies (2012) defines resilience as the ability to prepare and plan for, absorb, and recover from and more successfully adapt to adverse events. According to Haimes (2009), the vulnerability assessment primarily contributes to a system’s degradation state under an extreme event, whereas the resilience assessment goes beyond this point and includes the system’s recovery following extreme events. As a case in point, hardening of a system against region-specific hazards (i.e., pre-event investment) may reduce the vulnerability of the system to the hazards; however, if the recovery needs are not properly addressed, the resilience of the system in terms of recovery time and cost will not always be improved. To achieve an in-depth understanding of the resilience measures that help identify the most appropriate pre- and post- disaster activities, the resilience of the network in this report

5 is defined as its capacity to absorb, adapt to, and restore after a sudden shock. The shock absorptive capacity of the sys- tem is its ability to withstand a given level of stress without loss of function. For example, strengthening the bridge piers with steel jackets in seismic areas increases the capacity of the structure to resist ground vibrations that can eventually lead to a more robust network (Furtado and Alipour 2014 a, b, c). The adaptive capacity of the system shows the extent to which alternative components exist to satisfy performance requirements in the event of losses in some components of the network. For instance, implementing redundancy for the critical roadways and bridges in a transportation network increases the likelihood of having functional detours with acceptable lengths in case of failure of any of the links. The restorative capacity is the capability of the system to meet priorities and achieve goals in a timely manner so that recov- ery from a disruptive event can be accomplished as quickly as possible with minimum cost. The restorative capacity could be improved by a number of strategies such as having rapid damage assessment techniques that would help identify the source and extent of the structural problems, implementing emergency response plans that would define the responsi- bilities of different involved parties in the most chaotic times after the extreme event, holding regular training sessions for the agency personnel to be prepared for the aftermath of extreme events and be familiar with their roles, planning for the available repair and replacement resources, and many other strategies that could be considered to increase the speed of the recovery with the optimized resources. To maintain all the listed capacities, sufficient resources must be allocated to the system for mitigation actions prior to and for restoration efforts following the occurrence of extreme events. To better illustrate the concept of resilience, a system per- formance curve will be defined here. The system performance could be measured in terms of different measures such as con- nectivity, accessibility, drivers’ delay, and direct and indirect costs associated with the failures, etc. (Alipour and Shafei 2015). For further illustration, Figure 1 depicts the changes in an arbitrary system performance measure, Q(t), over time. A major decrease in the performance measure can be seen when an extreme event occurs (t0). Depending on the state of robustness, the absorptive capacity of the system is affected and the remaining performance may become less than what was expected for a network with no degradation. The cross-hatched area under the performance curve can be considered as an indicator of the resilience of the system. The importance of including the effects of deterioration mecha- nisms can be clearly seen by comparing the resilience cal- culated for the deteriorating state of the system with the one obtained for the pristine system (Shafei et al. 2012 and 2013 and Shafei and Alipour 2015 a, b). After the occurrence of an extreme event, the role of adaptive capacity can be recog- nized based on the time in which the recovery of the system begins (ti). This is an indicator of the state of redundancy and rapidity of the system. Finally, the restorative capacity of the system can be evaluated by the time in which the pre-disaster performance level is fully regained (tf). This reflects the state of resourcefulness of the system (Figure 1). It can be noted that all mitigation and recovery efforts planned for a large- scale system requires the expenditure of resources. Hence, in addition to the time-based measures, cost-based measures are investigated to obtain reliable estimates of the resilience of deteriorating highway transportation networks. To ensure a FIGURE 1 Estimation of the resilience measures through absorptive, adaptive, and restorative capacity of a system performance measure. tf1 Timet0 ti1 t0 tf2 < tf1 Timeti1 = ti2 tf2 < tf1 Timet0 ti2 < ti1 tf2 < tf1ti1 = ti2t0 Time Sy ste m P er fo rm an ce , Q (t) Sy ste m P er fo rm an ce , Q (t) Sy ste m P er fo rm an ce , Q (t) Sy ste m P er fo rm an ce , Q (t) Resilience

6 target level of resilience, appropriate management strategies will be to: (1) increase the absorptive capacity of the system by pre-disaster investment in those components deemed to be the most important or the weakest, (2) provide alternative options for the critical yet vulnerable components of the network to improve the adaptive capacity, and (3) invest in resources that enhance the restorative capacity of the system in case of extreme events. One of the key concerns regarding the definitions cur- rently available for resilience is the overemphasis on the pre- disaster activities designed to reduce potential losses (i.e., strengthening of the infrastructure), with less attention paid to the post-disaster efforts required for emergency response and recovery. The scarcity of resources from economic, technical, and organizational aspects has however limited the amount of strengthening that could go into the bridges in a transportation network. This is amplified even more with the stochastic nature of the extreme events and the concept that the decision makers do not have any definitive knowledge of what intensity event will hit next and which part of the transportation network it will affect. In addition, even when limited resources are avail- able, the hardening of the system to one hazard scenario does not necessarily protect it under other types of hazards or other scenarios. These statements underline the importance of hav- ing more effective post-event response strategies that would increase the recovery and restoration speed while ensuring the optimum use of resources. As part of the AASHTO Subcommittee on Bridges and Structures (SCOBS) efforts to increase the resiliency of bridges and consequently transportation networks under extreme events, this synthesis report reviewed the relevant lit- erature on the post-disaster activities including damage detec- tion, emergency response, and performance restoration for the bridges as one of the most important components of the trans- portation network. The effort will focus on current practices by transportation agencies, local authorities, and stake holders throughout the nation to detect bridge damage under different natural hazards with extreme nature using different remote, in situ, or portable monitoring and damage detection tech- niques, the decision-making process following the collection of the damage data in highly pressured emergency conditions, and the response and recovery actions following the event that would lead to restoration of the performance of the bridges. ROAD MAP OF THE REPORT Chapter two of this report provides an overview of the survey results in the form of tables and charts. In addition, a brief review of the hazards identified by the state engineer and those damage detection techniques mentioned are provided. Chap- ter three provides a technical background for the detection techniques, their applicability in extreme events, and emerg- ing technologies that could be implemented for a better and faster damage assessment after extreme events. Chapter four reviews the details from state responses with a focus on type of hazards, damage detection techniques, and availability of emergency response plans, and concludes with a synthesis of emergency response planning, based on information from the surveys and the agency cases in this chapter. Chapter five summarizes the survey results and future directions in research. Appendices A1 and A2 present the survey questions sent to the state bridge and hydraulic engineers, respectively. Appen- dix A3 provides the case examples supplied by the survey respondents. This report is accompanied by an E-Appendix that presents examples of successful emergency response plans developed and adopted by some of the responding states. A brief overview of these response plans is given in Appendix A4.