ANALYSIS ON CONSTANT-STRENGTH DUCTILITY DEMAND SPECTRA FROM THE DIFFERENT RESTORING FORCE MODELS

摘要

Elasto-plastic response spectra have an important role in providing aseismic design rules and the related parameters. There are two types of elasto- plastic response spectra. One is the constant- ductility strength demand spectrum and the other is the constant-strength ductility demand spectrum. From the new Standard of PROC for aseismic design, a static elasto-plastic analysis method or Pushover analysis method has been introduced. Pushover analysis method depends primarily on the form of lateral seismic load distribution and the objective displacement determined from an elasto-plastic response spectrum. Based on ATC-40, the objective displacement is determined from the intersection point between a structural capacity curve and a seismic response demand curve in the same coordinate reference. The seismic response demand curve may be given by the constant-strength ductility demand spectrum. In the process of computing the constant- strength ductility demand spectrum, restoring force models including bilinear system and trilinear system must be chosen. In order to find out the difference between bilinear and trilinear systems, the basic equation on a constant-strength ductility demand spectrum is deduced and the concerned conclusions are proposed.