Integrated Study of Existing Tsunami Design Standards

Abstract

As the tsunami threat across the Pacific coast becomes better understood, vertical evacuation structures are being widely considered in order to improve life safety. The design of such structures requires careful consideration of fluid-induced forces. Recently, core walls have been used as a preferred system for lateral force resistance in tsunami-resistant structures. These structures require high strength and stiffness provided by walls both orthogonal and parallel to the demands; detailing and limiting shear stress demands provide the necessary ductility. There are, however, potential challenges to utilizing core wall systems for tsunami-resisting systems. Primarily, walls orthogonal to flow tend to draw large hydrodynamic and hydrostatic forces during tsunamis. Therefore, accurate estimates of these demands are needed for the design of resilient structures. A four-phase research program utilizing integrated experimental and numerical methods was undertaken to investigate these demands and the efficacy of current design standards in providing reasonable but conservative estimates for the forces imparted. The first phase of the program used computational fluid dynamics (CFD) to simulate the experiments, building on prior research. The second phase used the results from the simulations to define the bathymetry in the flume and the placement of instrumentation. In the third phase, a 1:6 prototypical scale core-wall structure was tested in the large wave flume at the Hinsdale Wave Research Laboratory, a Natural Hazards Engineering Research Infrastructure (NHERI) testing facility. The experimental setup permitted the testing of the full core-wall system, including the pile foundation and rough estimates of the impact of soil restraint on the demand. Strain gauges, load cells, and pressure distributions were used to provide advanced measurements of the structural response. These measurements were then used to validate the modeling approach. The fourth phase involved comparing the measured peak forces from experiments to standard design equations for imparted force against structures due to tsunami inundation using data acquired from the experiments with the intent of investigating tsunami load demand imparted to a structure after an earthquake. Earthquake loads were not taken into account in experimentation or analysis; they simply dictate a building’s capacity against the initial event.