Development of a guideline for estimating tsunami forces On bridge superstructures.

SR 500-340"The Pacific Northwest is vulnerable to seismic events in the Cascadia Subduction Zone (CSZ) that could generate alarge tsunami that could devastate coastal infrastructure such as bridges. In this context, this paper describes thedevelopment of a guideline for estimating tsunami forces on bridge superstructures along the Oregon Coast. A multiphysicsbased numerical code is used to perform numerical modeling of tsunami impact on full-scaled bridgesuperstructures of four selected bridges \u2013 Schooner Creek Bridge, Drift Creek Bridge, Millport Slough Bridge, andSiletz River Bridge \u2013 located on Highway 101 in the Siletz Bay area on the Oregon Coast. Two different types ofbridge superstructure, deck-girder and box sections, are developed in the case of the Schooner Creek Bridge to studythe effect of geometry of bridge cross-section. The results show that tsunami forces on box section superstructures aresignificantly higher than the forces on deck-girder sections; therefore, the box section design might not be appropriateto be used in a tsunami run-up zone. Moreover, numerical simulation of a deck-girder bridge with rigid rails and withopen rail spacing, subjected to identical tsunami loads, was performed to examine the effect of rails on tsunami forces.The results suggested that horizontal and vertical tsunami forces on bridges with rails are larger than those on bridgeswith open rail spacing, up to 20% and 15%, respectively. These numerical results are finally incorporated into themathematical formulations from the existing literature to develop a simplified method for estimating tsunami forces onbridge superstructures. Appropriate empirical coefficients for bridge superstructures under tsunami loads wereevaluated based on an average value of the scattering data from the numerical results. The developed guideline isintended to be used as a preliminary guidance for design only as it did not account for uncertainties; thus, anappropriate load factor must be included in the calculations. A previous analysis of tsunami forces on the SpencerCreek Bridge on the Oregon Coast is revisited to examine the applicability of the guideline developed in the presentwork. This paper also presents the results of a study on the optimal number of CPUs for running fluid-structureinteraction (FSI) numerical models of bridge superstructures using LS-DYNA on high-performance computing (HPC)systems.