Near-fault acceleration pulses and non-acceleration pulses: Effects on the inelastic displacement ratio

Near-fault ground motions can impose particularly high seismic demands on the structures due to the pulses that are typically observed in the velocity time-histories. The velocity-pulses can be further categorized into either a distinct acceleration-pulse (acc-pulse) or a succession of high-frequency, one-sided acceleration spikes (non-acc-pulse).The different characteristics of velocity-pulses imply different frequency-content of the ground motions, potentially causing different seismic effects on the structures.This study aims to investigate the characteristics of the two types of velocity-pulses and their impacts on the inelastic displacement ratio (CR) of single-degree-of-freedom systems. First, a new method that enables an automated classification of velocity-pulses is used to compile a ground motion dataset which consists of 74 acc-pulses and 45 non-acc-pulses. Several intensity measures characterizing different seismological features are then compared using the two groups of records. Finally, the influences of acc-pulses and non-acc-pulses on the CR spectra are studied; the effects of pulse period and hysteretic behavior are also considered. Results indicate that the characteristics of the two types of velocity-pulses differ significantly, resulting in clearly distinct CR spectral properties between acc-pulses and non-acc-pulses. Interestingly, mixing acc-pulses and non-acc-pulses can lead to local ‘bumps’ that were found in the CR spectral shape by previous studies.The findings of this study highlight the importance of distinguishing velocity-pulses of different types when selecting near-fault ground motions for assessing then on linear dynamic response of structures.