New Seismic Design Provisions in Japan

The seismic design requirements in the Building Standard Law of Japan and associated regulations were revised in June 2000 toward a performance-based design framework. The performance objectives are (a) the safety and (b) damage control of a building at two corresponding levels of earthquake motions. The design earthquake motion is defined in terms of acceleration response spectrum at engineering bedrock. The amplification of ground motion by surface geology and the soil-structure interaction must be taken into consideration. The return periods of the earthquake motion of approximately 500 years and approximately 50 years are considered for life-safety and damage-initiation limit states, respectively. The response is examined by so-called "capacity spectrum method" by comparing the linearly elastic demand spectrum of design earthquake motions and the capacity curve of an equivalent single-degree-of-freedom (ESDF) system. The structure as designed is reduced to an ESDF system using a nonlinear static analysis under monotonically increasing horizontal forces. Equivalent damping is used to modify the demand spectrum taking into account the energy dissipation capacity of a structure at the prescribed limit states.