ANALYSIS OF NORMALIZED TIME-FREQUENCY RESPONSE SPECTRA FOR THREE SEISMIC RECORDS

Time-Frequency Response Spectrum (TFRS) is a three-dimensional spectrum, which includes three main characteristics of ground motion: amplitude, frequency characteristic and duration. Based on it, Normalized Time-Frequency Response Spectrum (NTFRS) was proposed and the NTFRS of three typical seismic waves were calculated. The comparison of three NTFRS shows that spectra amplitudes distributed along period axis and duration axis are different from each other; the large difference may cause different effect on the structures. One 12-storey reinforced concrete frame structure was analyzed by using elastic-plastic time-history analysis method. The comparison of the seismic response, structural damage curve and NTFRS of input ground motion shows that the maximum seismic response of structure might not be the cause of its collapse. It implies that the traditional response spectrum theory has limitation because in the theory the maximum elastic response of structures is used to make seismic design. It could be concluded that the Normalized Time-Frequency Response Spectrum is better for analyzing the characteristics of ground motions and the structural failure mechanism in the earthquakes.