Incremental Dynamic Analysis (IDA) is a parametric analysis method that has recently emerged in several different forms to estimate more thoroughly structural performance under seismic load. It involves subjecting a structural model to one or more ground motion records. This method considers both inherent randomness and model uncertainty, so it used to probabilistic analysis of structures at high seismic loading. The objective of this study is to improve efficient, but accurate procedures for probabilistic analysis of nonlinear seismic behavior of structure. According to the three-parameter Log-normal distribution more rationally describe maximum story drift ratio at a higher value of spectral acceleration. The traditional method based on two-parameter Log-normal distribution is compared with the presented procedure based on three-parameter Log-normal distribution on analytical data. Improvement in the probabilistic estimation of maximum story drift ratio demand are illustrate with a SAC-9 story, moment resisting frame building exposed to a set of 20 ground motion.
