Tsunami Resilient Designs of Buildings for California

摘要

The ASCE/SEI 7 Standards Committee has developed a new Chapter 6 - Tsunami Loads and Effects for the 2016 edition of the ASCE 7 Standard, 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. In these states, mitigation of tsunami risk to public safety requires a combination of emergency preparedness for evacuation and structural resilience of the critical facilities necessary for immediate response and economic / social recovery. The new ASCE 7-16 provisions for Tsunami Loads and Effects enables a set of analysis and design methodologies that are consistent with probabilistic hazard analysis, tsunami physics and hydraulic engineering principles. The Tsunami Design Zone is the area vulnerable to being flooded or inundated by the Maximum Considered Tsunami, which is taken as having a 2% probability of being exceeded in a 50-year period, or 1:2475 annual probability of exceedance. The Maximum Considered Tsunami constitutes the design event, consisting of the inundation depths and flow velocities taken at the stages of in-flow and out-flow most critical to the structure. These provisions include new Tsunami Design Zone maps for design based on explicit reliability targets for Risk Category Ⅲ and Ⅳ buildings and structures. Although Risk Category Ⅱ buildings and structures are exempt, the local jurisdiction is encouraged to require tsunami design for RC Ⅱ buildings and structures exceeding an appropriate mean height, in order to provide a greater number of buildings that will be life-safe and disaster resilient. The experience of past tsunamis is that full evacuation of the population is never actually achieved. 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. The purpose of this paper is to provide an overview of the technical methodology based on illustrative design prototypes for structural steel, and reinforced concrete / reinforced masonry buildings at various locations in California. This paper will also provide some initial guidance to coastal communities in California who may desire to implement economical tsunami design requirements for Risk Category Ⅱ buildings.