Tsunami Design Criteria and Load Cases of the Asce 7-16 Chapter 6, Tsunami Loads and Effects

Abstract eng:
The 2016 edition of the ASCE 7 Standard, Minimum Design Loads for Buildings and Other Structures includes a new Chapter 6 – Tsunami Loads and Effects. The ASCE 7-16 Tsunami Loads and Effects chapter has become the first national, consensus-based standard for tsunami resilience for use in the states of Alaska, Washington, Oregon, California, and Hawaii. The intent of these requirements is to improve on both the siting and design of new Risk Category III and IV buildings and nonbuilding structures built in Pacific coast communities. This paper explains the basis of the design flow conditions at a project site and the load cases of various hydrostatic and hydrodynamic loading conditions that must be considered when designing the overall structural system and individual structural members. The principal author is the Chair of the ASCE 7 Tsunami Loads and Effects Subcommittee, and the second author is a member of that subcommittee. 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. The tsunami design requirements in the ASCE 7 Standard vary by Tsunami Risk Category; tsunami design applies to essential and critical facilities necessary for immediate response and economic / social recovery. It may also be applied to other multi-story buildings where tsunami resilience is desired by a community. Using the ASCE Tsunami Design Geodatabase to obtain the design level hazard of tsunami Runup, the design flow depth and velocity at the project site location are then determined using the Energy Grade Line Analysis or the Site-Specific Inundation Analysis. The Energy Grade Line Analysis takes the runup elevation and inundation limit indicated on the Tsunami Design Zone map as the given solution point of a hydraulic analysis along the topographic transect from the shoreline to the runup point. The two-dimensional Site-Specific Inundation Analysis utilizes the Offshore Tsunami Amplitude, together with an effective wave period that is considered a conserved constant and other waveform shape parameters specified by the tsunami provisions. This numerical simulation includes a high-resolution digital elevation model of nearshore bathymetry and onshore topography. The flow conditions determined from one of the methods are then used to determine structural loading and scour effects for which the building or structure must be designed.

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