Target Structural Reliability Analysis for Tsunami Hydrodynamic Loads of the ASCE 7 Standard

Many coastal areas in the United States are subject to tsunami hazard. The public safety risk has been partially mitigated through warning and preparedness of evacuation, but community disaster resilience requires that critical and essential facilities provide structural resistance to collapse. Furthermore, there are coastal communities in the states of Alaska, Washington, Oregon, California, and Hawaii where there is insufficient time for evacuation. The Tsunami Loads and Effects Subcommittee of the ASCE/Structural Engineering Institute (ASCE/SEI) 7 Standards Committee has developed a new Chapter 6, titled “Tsunami Loads and Effects,” for 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 new ASCE 7 provisions for tsunami loads and effects implements a unified set of analysis and design methodologies that are consistent with probabilistic hazard analysis, tsunami physics, and reliability analysis. The purpose of this paper is to provide analysis of the structural reliability basis for tsunami-resilient design of critical and essential facilities, taller building structures, and tsunami vertical evacuation refuge structures. Probabilistic limit-state reliabilities are computed for representative structural components carrying gravity and tsunami loads, utilizing statistical information on the key hydrodynamic loading parameters and resistance models with specified tsunami load combination factors. Through a parametric analysis performed using Monte Carlo simulation, it is shown that anticipated reliabilities for tsunami hydrodynamic loads meet the general intent of the ASCE 7 standard as stated in its Chapter 1 commentary. Importance factors consistent with the target reliabilities for extraordinary loads (such as seismic events) are determined for tsunami loads.