National Academies Press: OpenBook

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

Chapter: Chapter Five - Project Findings

« Previous: Chapter Four - Review of Agency Responses
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Suggested Citation:"Chapter Five - Project Findings." National Academies of Sciences, Engineering, and Medicine. 2016. Post-Extreme Event Damage Assessment and Response for Highway Bridges. Washington, DC: The National Academies Press. doi: 10.17226/24647.
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Page 50
Page 51
Suggested Citation:"Chapter Five - Project Findings." National Academies of Sciences, Engineering, and Medicine. 2016. Post-Extreme Event Damage Assessment and Response for Highway Bridges. Washington, DC: The National Academies Press. doi: 10.17226/24647.
×
Page 51
Page 52
Suggested Citation:"Chapter Five - Project Findings." National Academies of Sciences, Engineering, and Medicine. 2016. Post-Extreme Event Damage Assessment and Response for Highway Bridges. Washington, DC: The National Academies Press. doi: 10.17226/24647.
×
Page 52

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50 applied in an aftermath of a chaotic event. The availability of such techniques and plans will result in a faster and more organized recovery of the system—be it an individual structure or a number of structures—which will decrease the down- time of the system as well as the direct and indirect costs asso- ciated with its damage and failure. With this fundamental concept in mind, this report reviewed the existing literature in rapid damage detection technologies that could be used for identification of damaged areas and structures in a timely manner after an extreme event. Further- more, the current state of practice when dealing with unforeseen failures (normally resulting from extreme events) and the emer- gency response plans followed by state departments of transpor- tation (DOTs) were studied. The study began with two surveys that were distributed to state bridge and hydraulic engineers as members of the AASHTO Subcommittee on Bridges and Structures and the AASHTO Technical Committee on Hydrol- ogy and Hydraulics. The surveys addressed three major thrusts: (1) type of hazards in terms of likelihood of occurrence, (2) type of damage detection in use for rapid assessment of damage in bridges, and (3) availability of emergency response plans. The results from the first thrust resulted in the identifi- cation of collision (mostly over-height) as the number one source of failures in bridges, followed by those with hydraulic sources such as scour and flood and debris flow. Collision is considered a man-made hazard that could result in major dis- ruptions in the performance of the transportation network at a local level. Depending on the speed and mass of the impacting vehicle (usually a truck) and the capacity of the structure that is being impacted, the extent of damage can range somewhere between minor damage to complete collapse of some com- ponents or the entire bridge. On the other hand, the failures resulting from a hydraulic event can be regionally distrib- uted. A single flood can result in multiple failures in an area. The failure of one bridge upstream can result in the washing out of multiple bridges downstream (owing to the impact of the floating debris). The extent of scour and the erosion of supporting elements of the bridges can be substantial, imply- ing that such hazards would result in failures or closures that will have an extensive regional impact on the service level of the transportation network. Also considering the extent of damaged bridges, a more organized approach is required to deal with consequences of a regionally distributed event. The results from the second thrust of the questions showed that all of the responding states used visual inspection (either The importance of resilience in transportation networks has grown parallel to the increasing traffic volumes on highways and roads and the continued construction of urban and subur- ban areas, trends that will continue well into the future. Infra- structure resilience can be improved after assessing its current state, thereby reducing its vulnerability to disruptions and extreme events, allowing plans for possible failures, flexibility during probable disruptions, post-event responses, and even- tual repairs. These components correspond to the preparedness, absorptiveness, adaptation, and recovery of a resilient infra- structure system. This can be done by analyzing the resilience of the infrastructure system, allowing a holistic approach that takes into account several different aspects to improve the network’s overall performance against disturbances. As defined in chapter one, resilience is the capability of a system to absorb the shock of an extreme event, provide alter- natives, and rapidly restore the system to its original perfor- mance or service level or even to a better more stable state. It can be noted that resilience is different from risk. Although often used interchangeably with risk, resilience is considered varying with the dimension of time, the time-dependent occur- rence of the event, and the related resilience measures, resil- ience assessment can be distinguished from risk assessment. Risk can be defined as the likelihood of experiencing damage or loss. Risk assessment is the analysis and determination of the probability of occurrence of an event and the consequences of it considering the vulnerability of the system exposed to the event. Several researchers use the measurement of risk to describe some aspect of system resilience because they are so closely interconnected. In “Integrating Risk and Resilience Approaches to Catastrophe Management in Engineering Sys- tems,” Park described resilience as an emergent property of what an engineering system does, rather than a static prop- erty the system has; therefore, resilience is better understood as the outcome of a recursive process that includes sensing, anticipation, learning, and adaptation, making it complemen- tary to risk analysis with important implications for the adap- tive management of complex, coupled engineering systems. In other words, the entirety of resilience is more of a process, not solely determined by the system response to a disruption, but also by its preparation and recovery. This definition highlights the importance of the applica- tion of techniques that are rapid and accurate in estimation of damage to the system and provision of emergency response, recovery, and restoration strategies that could immediately be chapter five PROJECT FINDINGS

51 cursory or hands-on) as the first tool when assessing damage to bridges. Bridge engineers used other techniques (mostly nondestructive testing) as a secondary approach for more accurate damage detection and localization and measurement of extent of damage. Both techniques would require access to the bridge. In case of hydraulic engineer respondents, the second most used technique after visual inspection was sonar surveys. The survey responses on the availability of emergency responses showed that 86% of states claimed to have an emer- gency response plan in place for extreme events. The follow-up interviews however revealed that not all of the response plans are necessarily tailored for bridge damages. Also, some of the plans primarily covered the mechanisms of receiving emergency funding rather than dealing with the technical and organizational aspects of the restoration and recovery of the bridges. Reviewing the collected responses revealed three major gaps and opportunities for development: • Identification of vulnerable bridges and the most impor- tant links of the transportation network. To identify vulnerable bridges, a quantitative (or at least qualitative) risk analysis approach is required. This will show the likelihood and intensity of different events at the location of a bridge and provide a measure of the bridge vulnerability to sustain such loads during its life cycle. The important bridges in the network could be identified using the techniques available through network science. Fur- thermore, the bridges could be weighted based on their impor- tance to the system (e.g., access to critical facilities or major business regions) and then ranked using network performance indicators. This could be implemented as a preliminary pri- oritization tool that would help organize the recovery and res- toration action in instances of regionally distributed extreme events that result in disasters. • Application of emerging techniques for remote sensing. Visual inspection is identified as the number one damage detection technique by both bridge and hydraulic engineers. Disaster response requires an assessment of damaged infra- structure as quickly as possible; however, data collection can be dangerous in an area after a natural disaster. Also, it may not be possible to rally enough survey teams to cover a large disaster area. Traditional disaster assessment practices involve both detailed and rapid ground surveys; however, these prac- tices can be limited by timeliness. Information provided by remote sensing technologies has been proven to be beneficial to detecting and locating damage. Three major remote sensing techniques that have recently been developed at the test-bed level have been introduced as pathways to integrating these techniques into rapid damage assessment of bridges. It is also worthwhile to highlight the role of structural health monitoring techniques that could be used to detect the state of the bridge under different types of hazards. Structural health monitoring is the process of observation of a structural system over time using periodically or continuously sampled dynamic response measurements from an array of sensors, the extraction of the damaged location, and the statistical analysis of these damages to determine the current state of the struc- ture health. The respondents showed a level of distrust in the alarms, data collected from these systems, and the costs asso- ciated with their maintenance. However, considering the high promises of the techniques in the field of damage assessment, specifically in cases with no access to the bridge location, more investments in the development of these techniques at least for important bridges is beneficial. • Development of robust and organized emergency plans dealing with the failure of the bridges. Considering that the capability of the system to return to its pre-event performance level is highly dependent on the speed of the recovery, which by itself is a function of the technical, organizational, and financial preparedness of the agency, it is important for the agencies to be proactive and create emer- gency plans that are tailored specifically for the bridges in their jurisdiction, recognize the hazards that they are facing, and determine what resources are available to them to conduct recovery actions. A review of the extreme events that can impede the perfor- mance of bridges and the service of the transportation networks it is evident that the competing demands; limited budgetary, human, and technical resources; and the urgency of system restoration underscore the importance of planning. Planning will reduce delays in response and help to avoid conflicts at a chaotic time. The establishment of repair and replacement priorities before an event will help guide decision making during the response and recovery process and help minimize the unintended consequences. With such an approach the decision-making authorities, law makers, and response and recovery teams will all be working toward established goals. Having a streamlined plan for response and recovery will also help to organize teams in a more efficient way to respond to unforeseen extreme events as it provides them with a hier- archy of actions to be taken. To have an effective planning tool, it is important that the process of response and recovery be prioritized. At a mini- mum, this process would include the following steps: • Assessment of damage to the transportation network at the component and network levels and identification of the roadways and links that will most likely be damaged. For this purpose, a detailed hazard characterization pro- cess and vulnerability assessment of the transportation systems both at the component and network level is required. The outcome of this analysis will highlight the

52 nodes and links of the network that are most likely to fail because of the considered events. • Prioritization of the response and recovery actions for damage assets: At this stage, critical facilities such as hospitals and police stations that are to be connected to transportation resources immediately after the event will be identified and prioritized. Next, the results of previous step are to be weighted based on the impor- tance to the performance of the system. Here different performance measures such as travel time and short- and long-term economic impacts could be considered. • Plan for a balanced portfolio of actions that could result in achieving the set goals for response and recovery. This will include (1) implementation of strategies to identify the extent of damage as immediately and accu- rately as possible (training of on-site inspectors, use of health monitoring data, use of remote sensing technolo- gies), the establishment of a clear line of communication with the inspection team and detection devices with the headquarters of transportation agencies; and (2) creation of regular training sessions for the response and recov- ery teams that would keep them up-to-date on the most recent organizational aspects of response, recent tech- nologies, and protocols. Appointments to the response and recovery teams are to be identified in advance of the event so that all members of the team can all understand their role in the recovery process and the actions they are expected to undertake during the recovery period. This team may include transportation planners, struc- tural engineers, emergency management experts, envi- ronmental experts, and first responders. The team should include individuals who have experience responding to disasters. It is important that the locations of resources with respect to potential risk areas, be identified and the pathways to acquiring materials, instruments, and a work force to such areas be optimized. • It is important that the different response and recovery approaches consider the component of time in addi- tion to cost–benefit analysis to ensure the choice of the most effective recovery actions that are conducive to a resilience response. Figure 25 provides a review of such approach. What are the outcomes and lessons? Where and from what are we at risk? What is the magnitude of the expected loss? How could we respond? How do we execute? 1 2 4 3 5 Resilience Enhancement in Face of Extreme Events Identify most relevant hazards, areas and transportation assets most at risk Calculate the expected loss across multiple hazard scenarios to assess uncertainty Build a balanced portfolio with detailed cost benefit assessment Implement a portfolio of responses considering barriers and feasibility Measure success to incorporate lessons learned as input in next decision cycle FIGURE 25 Holistic framework for enhancing resilience in face of extreme events.

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TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 497: Post-Extreme Event Damage Assessment and Response for Highway Bridges reviews the procedures that state departments of transportation and two local authorities, New York City and Los Angeles County, use to assess the damage in bridges in response to extreme events and conduct emergency response activities. Extreme events include those with geological sources (such as earthquakes and landslides), from hydro-meteorological sources (such as hurricanes and floods), or those of man-made origin, either accidental (such as truck crashes) or malicious (such as terrorist attacks).

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