Effect of Entrapped Air on Solitary Wave Forces on a Coastal Bridge Deck with Girders

Abstract

Recent tsunami and hurricane-caused destruction, and the possibility of both tsunami inundation and storms of even greater magnitude and frequency making landfall in the future, has focused attention on the vulnerability of coastal structures, and bridges in particular. Findings from a series of experiments measuring forces on a 1:35 scale bridge model impacted by a solitary wave with varying percentages of air relief openings (AROs) between girders are presented here. A range of water depths, wave amplitudes, and elevations of the model above the still-water level (SWL) are considered. Results show significant reduction of vertical uplift forces when AROs are added to the bridge model, particularly when the girders are fully elevated above the SWL or only slightly submerged, but relatively little effect on horizontal forces in the direction of wave propagation is observed. Buoyancy calculations show added hydrostatic force does not alone contribute to uplift forces, but rather a combination of hydrostatic force, wave impact force, and deformation of the wave must all be considered.