Tsunami-Resilient Building Design Considerations for Coastal Communities of Washington, Oregon, and California

Abstract

The ASCE/SEI 7 Standards Committee has incorporated a new Chapter 6, “Tsunami Loads and Effects,” in the 216 edition of the ASCE 7 Standard, Minimum Design Loads and Associated Criteria for Buildings and Other Structures. The ASCE 7-16 chapter on “Tsunami Loads and Effects” is the first national, consensus-based standard for tsunami resilience, applicable to the states of Alaska, Washington, Oregon, California, and Hawaii. Furthermore, this new tsunami design standard is included in the requirements of the 218 International Building Code. Taller structures in a community can provide effective secondary alternative refuge when evacuation out of the inundation zone is not possible or practically achievable for the entire population. Although Risk Category (RC) II buildings and structures are exempt from tsunami design according to the ASCE 7 Standard, local jurisdictions are encouraged to require tsunami design for RC II buildings and structures of designated occupancies exceeding an appropriate mean height, to provide more buildings that are life-safe and disaster resilient. It is necessary to evaluate several important technical factors to inform a jurisdiction’s decision to establish a threshold height of applicability for RC II buildings and structures; this evaluation requires structural engineering expertise as explained in this paper. For many locations in California, Oregon, and Washington, the current seismic design systemic capacity of buildings with minimum threshold heights that provide at least one level above the Maximum Considered Tsunami inundation level [between 7.62 m (25 ft) and 13.72 m (45 ft)] will be sufficiently strong to resist the overall tsunami design load. Coastal buildings with a minimum safe height above the inundation depth in several locations in Oregon and southern Washington would not have sufficient seismic design strength to resist tsunami loads. In these locations, options are discussed for implementing resiliency through tsunami strengthening and zoning policies.