Case Study for Tsunami Design of Coastal Infrastructure: Spencer Creek Bridge, Oregon

Abstract

The absence of tsunami load provisions in coastal infrastructure design has led to unchecked resistance capacity of bridges against one of the most eminent natural hazards on the U.S. west coast. The Spencer Creek Bridge, which was completely rebuilt on the Oregon coast in 2009, is a unique example to demonstrate development and implementation of site-specific tsunami loads during the design stage. Two tsunami models, the Cornell Multigrid Coupled Tsunami model (COMCOT) and the Finite-Volume Wave model (FVWAVE), defined the flow fields from three rupture configurations postulated for a Cascadia earthquake, which has a moment magnitude of 9.0 consistent with the seismic design of the bridge structure. Although both models produce comparable surface elevations at the site, the finite-volume formulation of FVWAVE provides higher flow speed because of its capability to conserve momentum and mass even with formation of tsunami bores. The FVWAVE results define the input to the computational fluid dynamic module of