Recent devastations caused by tsunami and hurricanes and the inevitability of future hurricanes making landfall have focused attention on the need to assess the vulnerability of coastal structures, and bridges in particular. Findings from a series of experiments conducted on an 1:35 scale bridge model with girders under a solitary-wave flow are presented here. Side panels are added to the bridge model to trap air pockets between the girders. A range of elevations is considered, including cases where the bottom of the deck is just above the water surface and girders are submerged, to where girders are fully elevated above the water surface. Wave parameters tested include four water depths and five wave amplitudes. A qualitative comparison is made between results for forces on the trapped-air model and results from the same set of wave parameters on a model where the side panels are removed and air is allowed to escape. Results show effects of water particle velocity, buoyancy, air compression and sloshing all have effects on both horizontal forces in the direction of wave propagation and vertical uplift forces. In particular, in the case where air is trapped between girders and cannot escape, uplift forces are considerably larger when bridge elevation is such that the girders are fully elevated above the still water level or are slightly submerged.

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