Estimation of Cascadia Local Tsunami Loads on Pacific Northwest Bridge Superstructures

Abstract

Abstract The time histories of Cascadia Subduction Zone (CSZ) local tsunami horizontal and vertical loads and the overturning moment on four selected Oregon coastal bridges are computed for different load scenarios. These scenarios, containing the tsunami-free surface elevation and flow horizontal velocity components, are developed using various CSZ rupture models. One of the bridges is selected to evaluate the effect of various bridge geometry characteristics on the resultant tsunami loads. Maximum tsunami horizontal and downward vertical loads are found to occur approximately simultaneously when the tsunami flow reaches the landward side of the bridge cross section and overtops the barrier. A comparison between tsunami loads on a deck-girder bridge and a box-girder bridge under identical tsunami flow condition reveals that on box-girder bridges, (1) maximum horizontal loads are slightly larger, (2) downward vertical loads are smaller, and (3) uplift loads are significantly larger. It is shown that bridg...