Evaluation of the Pulse-Like Nature of Near-Fault Ground Motions Using S-Transform

Near-fault seismic events have been popular research topics in earthquake engineering, especially, in last two decades. A variety of research programs have been conducted to characterize the unique nature of near-fault events from both structural and seismological point of views. In this paper, after the introduction of S-Transform as a modern timefrequency representation which can measure local characteristics of a signal such as amplitude, frequency, and phase at any time instant, a new robust filtering method is proposed and applied to extract the pulse-like part of nearfault ground motion records. Seven pulse-like near-fault recorded ground motions have been selected from literature such that the comparison of results with similar available methods can be possible. After the extraction of pulse-like parts, the nonlinear dynamic behavior of two 3-D reinforced concrete moment frames with 6 and 9 stories is studied by using Incremental Dynamic Analysis (IDA) under support excitation by original ground motions, extracted pulses and residual ground motions. To investigate the sensitivity of results to the pulse period, two extra steel moment frames with 3 and 12 stories are modeled. The results deeply questions the reliability of the application of low-frequency extracted pulses as the representative of original ground motions in dynamic time history analysis, especially, when the nonlinear behavior is considered.