Long-period characteristics of earthquake ground motions and aspects of seismic analysis of long-period structures

This paper summarizes the long-period characteristics of earthquake ground motions and provides conceptual guidance for the seismic analysis or seismic mitigation of long-period structures. To this end, 1500 real earthquake ground motions were selected from the PEER database and their response spectra were calculated by performing dynamic analyses of single-degree-of-freedom (SDF) systems at different structural periods. The results show that ground motions exhibit significantly different characteristics in the long structural periods compared to the short periods, namely, the impulse feature of ground motions at long-periods, smaller pseudo acceleration spectra than absolute acceleration ones, the "crossover" phenomenon of damping effects, developing the maximum seismic response at the same excitation time and the possible development of the maximum response after the end of shaking. Therefore, the following aspects should be carefully considered in the seismic design of long-period structures: (1) The error in the response spectrum analysis method might be significant, and thus it is recommended to employ the time history analysis method, where the dynamic analysis should be extended by half of the structural fundamental period, (2) The damping devices and design parameters should be well selected by taking into full consideration of the "crossover" phenomenon of damping effects.