Research On Design Spectrum Of Far-sourse Long-period Ground Motion Based On Seismic Records From 2008 Wenchuan Earthquake, China

The suitable long-period ground motion input is vital to seismic design of long period structure. In recent years, the research and practice on long-period ground motion input has made great achievement in Japan. However, due to the difference between Japan and China in earthquake environment and seismic design ideology, those achievements may not be copied. In China, the research on long-period ground motion input can't satisfy the demand of the engineering practice well, and controversy on the long-period design spectrum in Chinese codes never stops. Obviously, the adjustment of long-period design spectrum in code should vary with the type of ground motion. Thus, the design spectrum of common and long-period ground motion is researched respectively based on 2008 Wenchuan earthquake, China. The main contents of this study are as follows:(1) All the collected Wenchuan earthquake records are corrected and filtered, and the acceleration spectra, velocity spectra and related seismic parameters of these records are calculated.(2) The frequency spectrum parameters of all the seismic records are calculated and analyzed. Subsequently, combined with the epicentral distance and velocity peak value, the far-source long-period ground motion records are selected.(3) In order to improve the seismic input for long period structure, the design spectrum for common ground motion is obtained by the fitting analysis, and its parameters are calculated by the genetic algorithm.(4) Fiting analyses and parameters calculations of velocity design spectrum for farsourse long-period ground motion are made, and acceleration design spectrum is obtained with the help of pseudo-spectrum formula.The main conclusions are as follows:(1) The average period of acceleration spectrum(Tavg) is more suitable to evaluate the frequency spectrum properties of ground motions. Combined with Tavg, epicentral distance and PGV, a hybrid index is proposed to define the far-source long-period ground motion.(2) A new design spectrum for common ground motion is obtained. Besides, its parameters at different design conditions are given.(3) The genetic algorithm can give an accurate and precise estimate in spectrum fitting analysis.(4) A velocity design spectrum for long-period ground motion that coincides to Chinese seismic codes is obtained, and its parameters at different design conditions are given. In addition, a homologous acceleration design spectrum is built with the help of pseudo-spectrum formula. Compared to the design spectrum in codes, the newly-built design spectrum of far-source long-period ground motion can well reflect the spectrum properties of long-period ground motions.