Analysis On Intensity Measure Indices And Interstory Drift Spectrum Of Near-fault Ground Motions

Motion characteristics and structural effects of near-fault ground motions have attracted the close attention of researchers in seismic engineering all over the world, especially in some advanced countries like USA and Japan. This topic is becoming more and more important. Therefore, the researches around them will play a significant role in developing the new contents and innovational technology of seismic engineering. Based on 150 near-fault ground motion recordings from the great earthquakes including Chi-Chi earthquake in Taiwan, China and Northridge earthquake in USA, this paper analyzes the intensity measure parameters and interstory drift spectrum of near-fault ground motions.Firstly, based on the frequency characteristic of near-fault ground motions with remarkable long-period components, two intensity measure parameters are proposed, which are improved effective peak acceleration (IEPA) and improved effective peak velocity (IEPV). And the new characteristic period of these strong ground motions is defined based on IEPA and IEPV. Then, the nonlinear correlation relationships between 30 intensity indices of the near-fault ground motions and the maximum displacements and energy responses (input energy and hysteric energy) of bilinear single degree of freedom (SDOF) systems with different periods are analyzed. The computational results illustrate that there is no intensity parameter with strong correlation in the whole period range. Furthermore, the intensity measure parameters related to ground acceleration have the best correlation with the seismic responses for the rigid (short-period) systems; velocity-related parameters are better for the intermediate-period systems; displacement-related parameters are better for the flexible (long-period) systems. Moreover, the curves of correlation coefficients of pulse-like ground motions differ from that of non-pulse-like ground motions largely. The parameters IEPA and IEPV of the near-fault ground motions improve the performance of intensity measure of conventional parameters, i.e., EPA and EPV, respectively. And the new characteristic period based on IEPA and IEPV can reflect the frequency content of the near-fault ground motions well.Secondly, this paper examines further the influences of characteristics of near-fault ground motions, such as rupture forward directivity effect, fling-step effect and non-pulse motion, on the intensity indices and characteristic period. The numerical results show that the there are distinct differences among the near-fault ground motion with the three motion characteristics in the short, intermediate and long period respectively. The ground motions with fling-step effect have the maximum correlation between the representative intensity parameters and responses of SDOF systems.Finally, the interstory drift spectrum analysis of near-fault ground motions is implemented according to three categories of motion characteristics. It is concluded from the results that there are the obvious disparities in the interstory drift spectrum of three types of motion characteristics in the whole period; the interstory drift of continuous beam excited by velocity pulse from rapture forward directivity need to consider the influences of higher modes, while the interstory drift of continuous beam excited by velocity pulse from fling-step can obtain the approximate drift ratio only based on the fundamental mode response.