Force mechanisms of coastal twin T-girder bridges under tsunami waves with varying wave front profiles

Coastal bridges are threatened by tsunami waves, and substantial attention has been paid to tsunami forces on single bridges in recent years. However, the force mechanisms of coastal twin bridges remain inadequately understood, particularly the influences of girder clearance and girder gap under tsunami waves with varying wave front profiles. In this study, the interaction between tsunami waves and coastal twin T-girders is numerically investigated, and the dam-break waves are employed to generate tsunami waves with varying wave front profiles. The differences in force time histories between the seaward T-girder and the single T-girder are investigated, and the characteristics of the interaction process between tsunami waves and twin T-girders, together with their variations with the wave front profile, are revealed. The evolution of the horizontal and vertical peak forces on the twin T-girders and the corresponding shielding coefficients with girder clearance is then systematically investigated, followed by an examination of the effects of girder gap on the peak forces. The results indicate that the forces induced by tsunami waves with comparable heights but differing wave front profiles may vary by several times. The seaward T-girder markedly modifies the impact of the wave front on the landward T-girder, with this effect and the corresponding shielding coefficient governed by the girder clearance and wave front profile, as these factors significantly influence the energy dissipation at the seaward T-girder and the flow redistribution between the two girders. The maximum reductions in the horizontal and vertical peak forces on the landward T-girder reach 53.0% and 38.2%, respectively. The mechanism governing the evolution of peak forces with girder gap also depends strongly on the girder clearance and wave front profile. This study enhances the comprehension of the force behavior of twin girders under tsunami waves with varying wave front profiles.