Comparative Study On Different Rayleigh Damping Values In Soil Seismic Response Analysis

Soil seismic response analysis plays an important role in determining the surface ground motion parameters, and is an important research topic in earthquake engineering. The main methods of soil linear seismic response analysis include equivalent linear frequency domain analysis method and time domain step by step integration method. The only difference between time domain analysis method and frequency domain analysis method is the selection of different damping values, however, the root cause of difference among damping values is the frequency (the frequency is called target frequency in this paper) selected in solving the Rayleigh damping coefficient. In this paper, the results of time domain analysis and frequency domain analysis are compared with different Rayleigh damping values under different target frequencies, so as to provide a reference for the selection of the target frequency in the practical application of engineering. The main researches in this paper are summed as follows:1. One-dimensional time domain linear soil seismic response analysis procedure is developed, by which soil seismic response analysis with different Rayleigh damping values can be studied with numerical simulation method.2. The results of seven methods with different Rayleigh damping values in time domain analysis and frequency domain analysis are compared by one-dimensional soil models, and the results show that the selection of different target frequencies influencing viscous damping coefficient is the main reason leading to different results in time domain analysis. The results of time domain analysis match well with the results of frequency domain analysis, when full Rayleigh damping formulation and the first and the third natural frequencies are used.3. According to the site characteristic period in Code for Seismic Design of Building, combined with the empirical formulation of the first natural period of most multistory and high rise buildings, a new method determining target frequencies in full Rayleigh damping formulation in time domain analysis is put forward. In the new method, two target frequencies are respectively 1/(5Tg)and 1/Tg, and Tg is characteristic period of site. Practical examples are used to verify the new method, and the results of the new method match well with the results of the method using the first and the third natural frequencies and are also consistent with the results of frequency domain analysis, however, the new method is simpler and more convenient in application.At last, the research contents are summed up and the problems needed to be further studied are put forward.