Estimation and adjustment of eigenperiod of response spectrum of near-fault pulse-type ground motion

1387 acceleration recordings within 25 km of Joyner-Boore distance were selected from NGA database and grouped according to the Joyner-Boore distance and site condition. Then the characteristics of near-fault pulse-type ground motions were discussed by using different ways, including spectral characteristic, eigenperiod of response spectrum and the relationships with the Joyner-Boore distance and earthquake magnitude. The results show that: ① The number of near-fault pulse-type ground motions is related to the Joyner-Boore distance, but not to the earthquake magnitude. ② The period of velocity pulses is strongly related to the earthquake magnitude. ③ For near-fault pulse-type ground motion, it is more accordant with the reality to use dynamic peak period of pseudo-acceleration and pseudo-velocity response spectra of ground motion to calculate the eigenperiod of response spectrum. ④ The velocity pulses of ground motion has the effect of enlarging eigenperiod of response spectrum, and the enlargement scale of horizontal and vertical are the same. Moreover, the amplification is related to the site conditions, which amplifies more on the harder site. Based on the results of statistical analysis of near-fault ground motion mentioned above, the adjustment coefficient for eigenperiod of response spectrum in the current seismic design code is provided in this research, which is suitable for application in engineering. And the satisfied relationship between period of velocity pulses and earthquake magnitude is established based on the regression analysis.