Three-dimensional numerical investigation of floating debris effects on bridge superstructures during tsunamis

Catastrophic tsunamis occur around the world and as coastal communities continue to grow, consideration of cascading tsunami-borne debris effects on coastal structures becomes increasingly important. The objective of the present study is to address the gap in existing knowledge by advancing the fundamental understanding of the debris-tsunami-structure interaction of floating containers and quantifying the forces on representative bridge superstructures. To this end, a coupled SPH-FE modeling approach is calibrated against data from prior experiments and then used for conducting an extensive three-dimensional investigation. The results demonstrate that the initial water level, the elevation of the bridge and the bore properties have a significant effect on the debris trajectory, velocity and pitching, as well as, the forces on the superstructure. Moreover, there exist three different patterns in the debris-flow-deck interaction of containers aligned transverse to the flow (i.e. parallel to the bridge), which affect the direction of debris forces and their spatial and temporal evolution. Overall, the debris generates impulsive forces in both horizontal and vertical directions and consequently increase the total loads by a factor of 2.67 and 1.85, on average in the two directions, revealing the critical need to consider such effects in tsunami design guidelines and risk assessment frameworks.