Damping modification factors for displacement response spectra
Li Heng1,2 Wu Jianchao1,2 Lei Ting1
1. Hubei Key Laboratory of Earthquake Early Warning, Institute of Seismology, CEA, Wuhan 430071, China；
2. Wuhan Institute of Earthquake Engineering, Wuhan 430071, China
Abstract：In seismic design codes, damping modification factors (DMF) are used to adjust the elastic response spectral values with those critical damping ratios more than or less than 5%. The effects of earthquake magnitude, source-to-site distance and site conditions on the DMF for displacement response spectra are investigated. The results show that the DMF gradually approaches to 1 with the increase of the natural vibration period of the structure. The effects of magnitude and distance are obvious, and the influence of site class gradually diminishes with increasing distance. For a given period in which the magnitude or distance increases, the effect of damping on the seismic response may also increase, indicating that the response reduction due to the structural damping may become more efficient. Furthermore, the influence mechanism is analyzed. It can be concluded that the relative ratio of the low-frequency components of ground motion controls the DMF. The relative ratio is represented as the attenuation index of the acceleration response spectrum in the long-period range. A larger attenuation index corresponds to a faster approaching of the DMF curve towards unity with increasing the period. Based on these results, it is seen that the formula for DMF proposed in this work is applicable to the seismic design codes.
