Evaluation of characteristic peak ground acceleration (CPGA) as a ground motion intensity measure to reduce the dispersion of IDA curves

The intensity measure (IM), as an index of ground motion record, is one of the most important issues to reduce the dispersion of incremental dynamic analysis (IDA) curves. In this study, a modified version of peak ground acceleration (PGA) of ground motion record called characteristic PGA (CPGA) is proposed as a new ground motion IM to reduce the dispersion of IDA curves. To obtain CPGA, a ground motion is decomposed into several frequency components using the discrete wavelet transform, and frequency components with dominate frequency close to elastic and elongated period of the structure are selected. Then, a reduced version of the original record is reconstructed by superposition of these selected frequency components. The peak value of this reduced record in the form of an acceleration time history is defined as the CPGA. The efficiency of the proposed IM was considered via performing IDA analyses of three moment-resisting steel frames involving 3, 6 and 9 stories, using the CPGA parameter of 15 ground motion records. The results of IDA with IM of CPGA were compared with results of common IMs (i.e., PGA and spectral acceleration at the first-mode period of the structure (Sa (T1)) to measure the efficiency of the CPGA as IM. According to the results of IDAs, the IDA curves with IM of CPGA have less dispersion compared with PGA. Also, at the nonlinear stage, CPGA provides smaller dispersion for IDA curves than the Sa (T1).