Extraction of velocity pulses of pulse-like ground motions using empirical Fourier decomposition

Pulse-like ground motions may have only a distinct strong pulse or multiple pulses within the velocity time-history. These intrinsic pulses are hidden in low-frequency components that can impose extreme seismic demands on structures. This study presents a simple approach based on the empirical Fourier decomposition (EFD) to extract the intrinsic pulses of pulse-like ground motions. Based on the proposed approach, first, the original ground velocity is decomposed into several Fourier spectrum components (FSCs) via the EFD method. Among these FSCs, the significant low-frequency components are identified based on a proposed relative energy indicator (E-re). E-re is defined as the ratio of the Fourier square amplitude of the FSC to that of the original ground velocity. Next, pulse component is obtained by superimposing the minimum number of significant low-frequency components so that their total energy is above than 70% of the original ground velocity energy. Finally, the strong pulse is extracted from the pulse component by the peak point method. Results obtained by the EFD decomposed method are compared to those obtained from wavelet method for 91 pulse-like ground motions. The results show that the proposed method can extract the intrinsic pulses of pulse-like ground motions with reasonable accuracy. The proposed approach is further applied for classification of near-fault pulse-like ground motions in a dataset of ground motion records. According to the classification results, ground motions with a relative energy value greater than 0.30 can be characterized as pulse-like.