Determination of Hurricane Surge Wave Forces on Bridge Superstructures and Design/retrofit Options to Mitigate or Sustain These Forces

Abstract

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 wave forces 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 are the hurricane surge wave forces that coastal bridge superstructures and substructures need to be designed for, or retrofit for, to prevent them from being dumped in the water when hit by a hurricane; and to determine the behavior and performance of ALDOT’s I-10 bridges across Mobile Bay if so retrofitted for these forces, were the objectives of this research. The investigation was limited to a review of the literature, discussions with state DOT bridge engineers, discussions with coastal engineering researchers, etc. to determine the state of the art procedures for determining the magnitudes of hurricane surge/surface wave forces on coastal bridges and appropriate design actions to mitigate and/or sustain these forces. Qualitative analyses were performed to identify the primary hurricane surge/surface wave forces acting on coastal bridge superstructures and these were followed by quantitative analyses to determine the magnitudes of the primary surge/surface wave forces. Analytical assessments of the adequacy of the as-is I-10 bridge across Mobile Bay as well as an appropriately retrofitted I-10 bridge for a projected major hurricane passing directly through the bridge were performed.