Improved Capacity Spectrum Method using Inelastic Displacement Ratio

ABSTRACT: Capacity spectrum method (CSM) has been conveniently used for determined maximum roof displacement using both demand spectrum and capacity curve of equivalent single degree of freedom (SDOF) system for evaluating the seismic performance of buildings. However, conventional CSM specified in ATC 40 has been reported to underestimate seismic demand for a wide range of periods. In this study, the improved CSM method which is more simple and accurate is proposed. The proposed CSM method is that the maximum roof displacement is determined without iterating using inelastic displacement ratio and R factor calculated from demand spectrum and capacity curve. To evaluate the accurate of the proposed CSM method, three steel moment frames of 3-, 9-, and 20-story are considered. Nonlinear response history analysis (NL-RHA) for three frames is also conducted, which is considered as an exact solution. SAC Seattle 10/50 sets of ground motions are used. Moreover, this study estimates maximum story drift ratios using ATC-40 CSM and N2-method and compared with those from the proposed method and NL-RHA. The new proposed CSM proved to be more accurate than other previous CSMs