Design for Tsunami Loads and Effects in the ASCE 7-16 Standard

A tsunami is a series of great waves primarily caused by a major subduction-zone earthquake with large-scale displacement of the sea floor or by initiation of submarine landslides. Many coastal areas in the western United States are subject to tsunami hazard that is infrequent but potentially extremely destructive. The public safety risk has been only partially mitigated through warning and preparedness of evacuation; there are many coastal communities in the states of Alaska, Washington, Oregon, California, and Hawaii where there is insufficient time for complete evacuation, and places of higher elevation and/or taller structures could provide life safety. Community disaster resilience would also require that critical and essential facilities provide structural resistance to collapse. Towards that goal, the Tsunami Loads and Effects Subcommittee of the ASCE/Structural Engineering Institute (ASCE/SEI) 7 Standards Committee has developed a new Chapter 6 with design requirements for tsunami loads and effects, contained in the 2016 edition of the ASCE 7 standard Minimum Design Loads for Buildings and Other Structures [Minimum design loads for buildings and other structures]. The ASCE 7-16 “Tsunami Loads and Effects” chapter will become the first national, consensus-based standard for tsunami resilience for use in the states of Alaska, Washington, Oregon, California, and Hawaii. The purpose of this paper is to provide an explanation of the technical basis and methodology for tsunami-resilient design of critical and essential facilities, tsunami vertical evacuation refuge structures, and other multistory building structures. The ASCE 7 provisions for tsunami loads and effects implements a unified set of analysis and design methodologies with design maps based on probabilistic hazard analysis, loads based on tsunami physics, and a structural ultimate strength basis of design. Probabilistic offshore tsunami amplitude maps and tsunami design zone inundation maps were developed using a method consistent with probabilistic seismic hazard analysis in the treatment of seismic source uncertainties. Procedures for tsunami inundation analysis are based on using mapped values of offshore tsunami amplitude or the runup and inundation limit shown in tsunami design zone maps. The ASCE 7 “Tsunami Loads and Effects” chapter is consistent with the principles of probabilistic hazard analysis, tsunami physics, and fluid mechanics, integrated into a comprehensive set of design provisions.