The New ASCE Tsunami Design Standard Applied to Mitigate Tohoku Tsunami Building Structural Failure Mechanisms

The last decade of destructive tsunamis in the Indian Ocean, and Pacific Ocean near Samoa, Chile and Japan have demonstrated the increasing vulnerability of coastal populations and built infrastructure to this hazard. In the United States, a new chapter has been developed for the ASCE 7 loading standard to design important buildings and other structures for tsunami loads and their effects. The application of the proposed ASCE 7 tsunami design provisions is demonstrated in the context of reinforced concrete and structural steel buildings analyzed for tsunami loads from the March 2011 Tohoku Tsunami, where the details of their structural performance were surveyed. Based on the case studies, the Energy Grade Line method of analysis is shown to be a reliable and generally conservative method to determine flow depth and velocity at a site based on a known maximum runup, with a modification to the Froude number coefficient for the bore condition. The load equations and conditions of ASCE 7 resulted in reasonable and conservative estimates of forces on components for hydrostatic buoyancy, lateral hydrostatic and hydrodynamic forces. Mid- to high-rise buildings, which are optimal for tsunami refuge, can be economically designed for life safety or better performance for large tsunamis with local strengthening of relatively few components.