Experimental investigation of focused wave action on coastal bridges with box girder

The waves generated by hurricanes, together with storm surges, have led to severe damage and even failures in many coastal bridges in the Gulf of Mexico. Several studies have been conducted to investigate the effects of wave action on coastal bridges over the past 15 years. However, most of the existing research, both experimental and numerical, has used a regular or irregular wave as the incident wave; this cannot accurately and efficiently reproduce the features of hurricane waves. In this study, a periodical focused wave (PFW) was employed to experimentally investigate wave actions on coastal bridges. A coastal bridge model including a deck and box girder was set up in a wave flume to measure wave forces. PFWs with different peak frequencies and main crests were calibrated in the empty flume, and then were used to observe the wave action on the bridge model at different clearances. Using a smoothing method, the quasi-static and slamming parts were separated from the total wave forces. The experimental results show that the maximum horizontal and vertical wave forces both occur at approximately the time when the overhanging deck is fully submerged and wave water begins to overlap the bridge deck. The vertical quasi-static force is almost linear in relation to the main crest and clearance, but the horizontal and vertical slamming forces show a complicated tendency. The relationships between the dimensionless wave forces and relative maximum amplitude/wave steepness are studied, along with the relative relationships between the wave force components. The experimental results are also compared with those from two existing methods.