Vertical Evacuation Structures Subjected to Sequential Earthquake and Tsunami Loadings

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In extreme events, such as major earthquakes or tsunamis, public safety is a primary concern. A major subduction zone earthquake could cause a large tsunami, which could render constructed infrastructure near the coastline, traditionally designed for only seismic loads, to be severely damaged and result in loss of life. In coastal regions at low elevations, it may be difficult to quickly move to higher ground in the short time between the initial ground shaking and the arrival of a tsunami from a subduction earthquake. However, a vertical evacuation structure (VES) could provide refuge, with the most promising VES for large coastal populations being buildings with lower stories capable of resisting the sequential earthquake demands and tsunami loads. This research will investigate a new structural system for a building to serve as a VES, where the structural elements are continuous from the end of the pile to the top of the structure. This new system will use the above-wave-height stories for evacuation; the lower (below wave) stories will use connections that allow walls and slabs of the lower, non-evacuation floors to "breakaway" at the highest water level. Although counterintuitive, this breakaway system will reduce the tsunami load demands on the structure, further protecting the building and its occupants. This research will investigate the interactions of the structure, soil, and tsunami waves for both traditional systems designed only for seismic loads and the new breakaway structural system. The results of this research will provide first-of-its kind data for this new type of VES, which can improve life safety in tsunami-prone regions and provide course-ready material for graduate-level classes and seminars for researchers and practitioners. Data from the project will be archived and made publicly available in the NSF-supported Natural Hazards Engineering Research Infrastructure (NHERI) Data Depot (http://www.designsafe-ci.org). Although evacuation structures have been built in tsunami-prone regions in Japan and the United States, they are typically low-rise structures with limited shelter capacity. In contrast, taller structures could serve dual purposes, such as a hotel with lower stories housing retail or conference rooms, with upper levels designed for evacuation. Under earthquake loading, buildings are expected sustain damage in the maximum credible event and, unless specific to the site, soil-structure interaction is neglected. This design philosophy would not serve for a VES, which must be designed to: (1) remain damage-free during the maximum credible earthquake, (2) sustain the maximum considered tsunami at the lower floors, including horizontal and vertical forces, where initial research shows that these tsunami force demands can be two to five times the design earthquake forces, and (3) account for changes in the stiffness and strength of the soil due to liquefaction and scour. This research will address the fundamentals of sequential earthquake and tsunami hazard building performance to serve as a VES, accounting for full nonlinear soil-structure-wave interaction. Two structural systems will be studied: exterior concrete walls, which are a traditional structural solution for seismic loads, and a new structural system utilizing continuous concrete filled tube pile-column frames with breakaway connections at the floors below the inundation depth, tuned to fracture at specific loading resulting from hydrostatic buoyancy. The research activities will involve the following: (1) investigate fundamental characteristics of the soil-structure system through computational simulation, (2) experimentally study tsunami demands on the structure using the NHERI Large Wave Flume at Oregon State University, (3) analytically couple the tsunami demand and structure-soil response analyses using the NHERI Computational Modeling and Simulation Center resources, and (4) combine the findings to evaluate current and establish new design methodologies for VESs subjected to sequential earthquake and tsunami hazard loading.