An Evaluation of Inelastic Seismic Design Spectra

After reviewing general methods available for determining seismic design forces for structures which can tolerate limited amounts of inelastic deformations, the reliability of two representative procedures is evaluated. In the methods evaluated, inelastic design response spectra are obtained by modifying a linear elastic design response spectrum in terms of a specified ductility factor as suggested by Newmark and Hall and the Applied Technology council. The effect of different accelerograms, as well as of different system damping and hysteretic characteristics, on the inelastic response of single degree-of-freedom systems designed using these methods is thoroughly investigated, considering maximum displacement ductilities, maximum and permanent drifts, number of yield events, and hysteretic energy dissipation. Application of these design methods to multistory buildings is also briefly considered. Results obtained for ideal inelastic systems indicate that these methods do not reliably limit displacement ductilities to specified values.