Experimental investigation of wave forces on superstructures of coastal bridges with curved box–girders

Wave-induced loads on coastal bridge superstructures have been widely studied; however, the influence of curved box–girder geometry on wave impact remains insufficiently understood. This study presents a hydrodynamic experimental investigation of wave forces acting on a coastal bridge superstructure with a curved box–girder under regular waves with varying periods, amplitudes, and clearance conditions. Vertical and horizontal wave forces were measured using three-component load cells, and local pressures were recorded by an array of pressure sensors. The results show that the loading mechanism is strongly governed by the submergence condition. The most critical impacts occur under shallow-submerged conditions (−0.04 m ≤ C ≤ 0.00 m), where air–water interaction produces sharp pressure peaks and amplified wave forces. The slamming component gradually diminishes and approaches zero when the relative parameter (A−C)/h_d exceeds approximately 0.4. Pressure measurements indicate that the maximum impact consistently occurs near the frontward underside of the girder. Under zero-clearance conditions, short-period waves generate broadband slamming responses with peak amplitudes about 65% larger than those of long-period waves, while the impact energy attenuates by over 90% along the girder. These findings provide experimental data and practical guidance for evaluating wave loads and determining safe clearance requirements for coastal bridges with curved box–girder superstructures.