Hurricane Surge/Surface Wave Forces on Deck-Girder Bridges and Design/Retrofit Options for These Bridges

An increasingly common occurrence when strong hurricanes come ashore along the Gulf of Mexico is that the hurricane surge/surface waves lift and push the superstructures of coastline bridges from their support bents into the water. It appears that the superstructures of many of these coastal bridges are not positively connected, or only minimally connected, to the supporting pile bent caps. This lack of adequate connection may be due to anticipation that the hurricane surge/surface waves will not reach the elevation of the superstructure, or it may be that the anticipated surge/surface wave forces are considered to be too great to economically design to resist. However, based on the performances of some closely adjacent bridges across Lake Pontchartrain when Hurricane Katrina came ashore in August 2005, it appears that it should be very feasible to connect new bridge components, or to take retrofit action for existing bridges, in a manner to avoid having hurricane surge/surfaces waves dump the bridge superstructure into the water. Determining what is the appropriate design hurricane sea state at the I-10 bridges across the north end of Mobile Bay and the surge/surface wave forces that this sea state would apply to the bridge superstructure and substructure was the purpose of this research. The investigation was limited to a review of the literature, discussions with state DOT bridge engineers and discussions with coastal engineering experts to determine the mode and sequence of failure of coastal bridges as hurricane surge/surface waves pass through these bridges. Using these same sources of information, a design hurricane sea state and its associated design storm surge/surface wave forces were estimated for the I-10 bridges. An analytical assessment of the adequacy of the as-is I-10 Mobile Bay bridge as well as an appropriately retrofitted I-10 bridge for the estimated design hurricane passing directly through the bridge was performed. Conclusions and recommendation resulting from the analyses and assessment are presented.