Influence of permanent displacement of ground motion on seismic response of structures

When calculating the seismic response of a structure based on the displacement excitation, the displacement excitation is obtained by integration of the velocity, which is obtained by integration of the acceleration records. At the same time, the acceleration noise must be removed. However, limited by the method for eliminating noise from acceleration records, the permanent displacement of the ground motion in the near-fault earthquake acceleration records is often weakened or even eliminated. This makes it impossible for researchers to judge the effect of permanent displacement of ground motion on the seismic response of structures excited by displacement. In this paper, the authors deduce the pseudo-velocity spectra formula of single degree of freedom system based on displacement excitation, verify the accuracy of the formula with the constructed pulse displacement time history, and then analyze the effect of the permanent displacement of the ground motion on the pseudo-velocity spectra. Firstly, the noise is executed on the acceleration records via wavelet transform, and gound motion with permanent displacement is remained. And then the permanent displacement is wiped out using reducing trend item method or filtering method from those records. Those excitations are used to calculate pseudo-velocity spectra. The results show that in short period, the pseudo-velocity spectra are similar whether ground motions contain the permanent displacement or not; in medium-long period, the pseudo-velocity spectra excited by non-permanent displacement excitation are lower than those by displacement excitation with permanent displacement, and this kind of difference are enlarged when the filtering method is used. Therefore, for seismic design of long-period structures, the ground motion with permanent ground displacement excitation should be used, or reducing trend item method is used to wipe out permanent displacement.