FORMULATION OF DURATION-DEPENDENT INELASTIC SEISMIC DESIGN SPECTRUM

In this paper, a procedure for developing the duration-dependent inela stic seismic design spectrum is proposed. The approach assumes that th e lateral strength of the structure can be increased to compensate for the increased number of inelastic cycles that may be imposed on the s tructure under a long duration ground motion. Seismic input energy is considered as a part of the demand on the structure, and an empirical prediction of the seismic input energy in terms of the ground motion d uration is made. Seismic design is established by requiring the struct ure to have a cyclic plastic strain energy capacity that is larger or equal to the portion of the seismic input energy contributing to cumul ative damage. The plastic strain energy capacity of the structure is c alculated using an energy-based cumulative damage model. Results from this study indicated that an increase in the lateral strength demand c an be expected for an increase in the duration of the ground motion, a nd the increase in lateral strength is largest near the characteristic period of the ground motion. The strength deterioration parameter tha t characterizes the plastic strain energy capacity of the structure ha s been found to have a significant influence on the duration-dependent inelastic seismic design spectrum.