Study of Tsunami-Induced Fluid and Debris Load on Bridges using the Material Point Method

Abstract

This research focuses on the development of techniques for the material point method (MPM) modeling the fluid-solid interaction, and gives preliminary results for researchers and engineers trying to understand the demands on bridge superstructures by tsunami-driven debris. First, a numerical flux smoothing algorithm is proposed to stabilize (nearly) incompressible fluid simulations with a control mechanism (i.e. numerical flux). Secondly, an enhanced boundary modeling technique is presented to decouple the geometries of grids and boundaries, by introducing boundary specific force fields for applying boundary conditions. Both of the newly developed algorithms are validated with numerical examples and test cases, ranging from fundamental hydrostatic problems to tsunami flows interacting with bridges. In the end, with the new algorithms, debris-induced loads, impacts and loads caused by damming effect, on bridges during a tsunami are studied. Results show (1) tsunami-driven debris can significantly increase demands on bridges compared with no-debris cases; (2) when flow is partially blocked by debris, peak horizontal forces are proportional in the order of about 3.6 to net cross-section area of the water flow at initial conditions; (3) impact forces are related to contact areas and propagation path of stress waves; and (4) contribution of water flow to the debris-induced impact forces can vary from 25 to 35 percent of those in the corresponding in-air cases.