Storm Surge and Wave Loading on Bridge Superstructures

A number of major bridges have been severely damaged or destroyed by hurricane generated storm surge and waves during the last few years. Examples include the I-10 Bridges over Escambia Bay near Pensacola, Florida during Hurricane Ivan in 2004, the US 90 Bridges over Biloxi and Saint Louis Bays in Mississippi and the I-10 Bridges over Lake Ponchartrain in Louisiana during Hurricane Katrina in 2005. With global warming and sea level rise some scientists are predicting that both the frequency and intensity of these storms will increase during the coming decades. It is important that these loads be considered in both the analysis of existing bridges and the design of new bridges located in coastal waters. Even though significant effort has been devoted to the development of predictive methods for wave loads on vertical structures such as piles, seawalls, etc. horizontal, bridge span like structures have received little attention. Existing work in this area has been mainly directed at offshore platforms or open coast piers and ocean wave conditions. Wave conditions in coastal waters are different from those in the ocean and on the open coast. The periods and, therefore, the lengths of waves in coastal waters are much shorter. This results in large variations in wave-induced water particle velocities and accelerations over the width of a bridge span with corresponding variations in wave forces. This paper reports the results of a study to develop a mathematical model for predicting storm surge and wave forces on bridge superstructures. Also included is a description of physical model tests conducted in a wave tank at the Coastal Engineering Laboratory at the University of Florida to determine: 1) inertia and drag coefficients in the model and 2) information needed to predict wave-induced slamming forces.