Structural Vulnerability of Coastal Bridges Under Extreme Hurricane Conditions

This work presents the results of a numerical study evaluating the response of coastal bridges due to hurricane-induced waves. The analyses were conducted using the Coupled Eulerian-Lagrangian (CEL) approach, available on the commercial finite element software Abaqus, which allows modeling the interaction between water and the bridge. The work concentrated on (1) establishing an approach for modeling the desired wave characteristics (i.e., wave height, and frequency) within the CEL simulation, (2) conducting simulations using actual bridge dimensions of historically damaged bridges, (3) analyzing a range of foundation flexibilities to determine its effect on the uplift and shear forces acting on the superstructure, and (4) comparing results simulations to AASHTO equations that estimate wave forces acting on coastal bridges. The numerical study revolved around two major highway bridges damaged along the U.S Gulf Coast during hurricane Katrina in 2005, (a) the U.S 90 highway bridge over Biloxi Bay and (b) the US. 90 St. Louis-Bay Bridge. The water level elevation was defined at the bottom of the superstructure as post-Katrina investigations revealed that this was a common characteristic for damaged bridges. The analysis revealed that (a) bridge models with flexible foundations provide better force design estimates than models with rigid supports, (b) the force demands are presumably amplified when the natural frequency of the bridge coincides with that of the traveling waves, and (c) CEL force estimates show large peak magnitudes during wave impacts that exceed AASHTO estimates. Further research is required to determine if these peaks are numerical artifacts or a concern for connection design