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PostâExtrEmE EvEnt DamagE assEssmEnt anD rEsPonsE for HigHway BriDgEs Transportation systems form the backbone of the economy, everyday life activities, and emer- gency response and recovery actions. Bridges are essential to the performance of the trans- portation system, but act as bottlenecks in the event of any failures adversely affecting the overall performance of the system. Extreme events, including those with geological sources (such as earthquakes and landslides), hydro-meteorological sources (such as hurricanes and floods), or man-made sources either accidental (such as truck crashes) or of malicious origins (such as terrorist attacks) pose a serious risk to transportation systems. For this purpose, it is important to increase the resilience of the system in face of extreme events. Resilience is an indicator of the absorptive capacity and adaptability of the system, in addition to its capabil- ity to rapidly restore its capacity. It can be useful to a range of management teams such as policy makers, engineers, and emergency service workers. Absorptive capacity is a measure of strength, describing how adept a system is at simply resisting the forces of disruption. The existence of alternative paths and options in a network is represented by the level of adapt- ability; in a transportation network this may refer to the range of combinations of roads and highways allowing a vehicle to travel between the same origin and destination. Post-event, the ability to efficiently identify and respond to the sustained damages, dispatch resources, and facilitate repairs reflects the system responsive capacity. One of the major aspects affecting the response capacity of state departments of trans- portation (DOTs) when facing extreme events is the capability to quickly assess the extent of damage to the bridges and make fast and effective decisions that would result in rapid recovery of the damaged components and the system as a whole. This NCHRP synthesis was conducted to review the procedures that state DOTs and two local authorities, New York City and Los Angeles County, take to assess damage in bridges and undertake emergency response activi- ties following extreme events. Two separate surveys were distributed, one each to state bridge engineers and state hydraulic engineers, and follow-up interviews were conducted to ensure a thorough collection of experiences that state DOTs have acquired after recent extreme events. Forty-three of 50 state bridge engineers responded to the survey (a response rate of 86%), and 42 of 50 state hydraulic engineers responded to the hydraulic survey (a response rate of 84%). The surveys addressed three major areas: (1) the 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 area resulted in the identification of collisions (mostly over- height vehicles) as the number one source of bridge failures, followed by those with hydraulic sources such as scour and flood and debris flow. Collisions are considered to be a man-made hazard that could result in major disruptions in the performance of the transportation network at a local level. Depending on the speed and mass of the impacting vehicle and the capacity of the structure being impacted, the extent of damage can range between minor damage to complete collapse of parts or the entire bridge. On the other hand, failures resulting from hydraulic events can be regionally distributed. 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 (because of the impact of the floating debris). The extent of scour and erosion sUmmary
2 of supporting elements of a bridge can be significant, implying that such hazards could result in failures or closures that would have an extensive regional impact on the service level of the transportation network. Also, when considering the extent of bridge damage a more orga- nized approach is required to deal with the consequences of a regionally distributed event. The results from the second area of surveys showed that all of the responding states used visual inspection (either 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 localization and detection. Both techniques would require access to the bridge location. For the hydraulic engineer respondents, the second most frequently used technique after visual inspection was the sonar survey. Survey responses showed that 86% of states claimed to have an emergency response plan for extreme events. The follow-up interviews however showed that not all of the response plans are tailored for responses to bridge damage. Also, some of the plans focused primarily on the mechanisms of receiving emergency funding rather than dealing with the technical and organizational aspects of bridge restoration and recovery.
