Lessons from Hurricane Ike

Ch9: Lessons in Bridge Infrastructure Vulnerability

9 Introduction the performance of regional bridge infrastructure has a significant impact on the safety, effectiveness, and efficiency of the transportation system following hurricane events, which is crucial to facilitating post-event response and recovery activities (Fig. 9.1). hurricane ike caused notable damage to the infrastructure of the houston/ Galveston Area when it made landfall on September 13, 2008. Many local bridges were completely destroyed and although the majority of these were small timber structures in rural areas, multiple major bridge structures also suffered damage from debris, storm surge and wave loading. Much of the damage can be attributed to inundation of the decks, or superstructures, of the bridges, debris impact, and erosion of abutment supports and approaches. this chapter presents a holistic overview of the damage to bridge infrastructure in the houston/Galveston area caused by hurricane ike. typical failure modes are evaluated by assimilating a rich data set of postevent assessment surveys and inspection reports. the data assembled include field reconnaissance conducted by the authors, hntB (a nationwide bridge design firm) through the texas department of Rural Affairs, the texas department of transportation, and interviews with local municipalities or other bridge owners. the performance of timber bridges, often located in rural areas, as well as major highway bridges is assessed. the damage summaries presented include a discussion of factors contributing to the damage, repair procedures, and simple capacity /demand checks for case studies in which bridges over water crossings were damaged during ike. Assimilation and assessment of the empirical data from such natural disasters provides key lessons for improving the performance of infrastructure given potential exposure to future events of an even greater magnitude. the chapter concludes with a summary of lessons learned, recommendations for mitigating future damage, and needed future studies that can benefit from this investigation. lessons in Bridge infrastructure Vulnerability Jamie E. Padgett and Matthew Stearns 107 Figure 9.1. the i-10 highway bridge near Pass Christian, Mississippi was seriously damaged by the storm surge associated with hurricane Katrina that lifted sections of the bridge up and off. Photo courtesy John Fleck/ FEMA. Bridge Infrastructure Vulnerability 108 Damage to Bridge Infrastructure Both timber structures as well as major highway bridges are considered in this reconnaissance study. Much of the damage experienced can be attributed to storm surge and wave loading on the bridge superstructures. the damage or destruction of 26 structures has been ascribed to these loads. in order to find the levels of storm surge and wave heights experienced by areas along the Gulf of Mexico in the houston /Galveston Area, SWAn and AdCiRC modeling was conducted at the University of texas at Austin (dawson and Proft 2010). this modeling was discussed in chapter 5. the models revealed that the peak storm surge level was in excess of 14 feet in some locations , while wave heights reached values of over 5 feet near Rollover Pass. the hindcast data was further used to identify the surge and wave height at locations where bridge damage occurred , and was evaluated and compared relative to the hazard estimates. twenty-five bridge structures were subject to scour around the abutments and wing walls of the bridges, and four local bridges suffered from impact damage caused by debris. the impact damage caused spalling, or the chipping off of portions of concrete. damage to surveyed bridges is summarized in table 9.1. the bridge type noted in the table refers to the superstructure and substructure material of the bridge. the state of damage is characterized by the level of damage incurred andisassignedbasedonthedefinitions provided in table 9.2. For example, visible , repairable damage to the structure that does not affect the structural integrity is deemed light damage. Using the data from the hurricane ike SWAn and AdCiRC simulations , the maximum storm surge and wave heights were found along the coast and plotted in fig. 9.2 relative to the bridges and their respective damage states. the figure excludes 17 rural bridges located further inland that also experienced damages from hurricane ike but were not located in the surge zone. these bridges were likely damaged by heavy rains that accompanied the storm as it moved further inland. the following sections provide a summary of the findings of the reconnaissance data accompanied by a detailed discussion of these failure modes for different bridge types. to define the terminology, fig. 9.3 shows a general bridge layout showing the key components...