A Study of the Safety Factor of the Capacity Spectrum Method for Multi-Story Structures

A Study of the Safety Factor of the Capacity Spectrum Method for Multi-Story Structures

Currently, engineers in Taiwan often use pushover analysis based on the capacity spectrum method to make detailed seismic evaluations of structures. The performance-target ground acceleration is compared with the peak ground acceleration(PGA) at the site of a design earthquake with a 475-year return period to evaluate the sufficiency of a structure’s seismic capacity. However, according to FEMA 440, these evaluated results are too conservative for short-period structures. In this report, a nonlinear dynamic analysis of five-story and ten-story structures is performed to study the inherent safety factor of the capacity spectrum method and its relationship to the story number, the dispersive hysteretic energy, and the characteristics of the input seismic record. From the analysis results, this safety factor is found to be 3.09 for the five-story structure and 3.43 for the ten-story structure. It is also found to be less affected by the dispersive hysteretic energy, and to be influenced by the characteristics of the input seismic record. Although the analysis error of the capacity spectrum method with a single mode is probably larger for high-rise buildings than for low-rise buildings, the capacity spectrum method still has a high value for the safety factor.