Synthesized Ground Motion Based On Time Domain Pulse Function

The ground motion adopted in seismic analysis of structures mainly originated from the natural ground motion record,the purely artificial ground motion and the semi-artificial ground motion by means of the modulation of the natural ground motion record to fit the target response spectrum.When the priority projects such as high-rise structures,long-span bridges,large-scale liquid-storage tanks,etc.,are performed the seismic analysis of structures,the appropriate input ground motion is selected according to the specific site conditions and the magnitude and the epicenter distance of ground motion.Furthermore,it is usually required that the response spectrum of the appropriate input ground motion is compatible with that of the design response spectrum.However,the natural ground motion data is hard to meet the requirement It is also necessary to make the response spectrum of the input ground motion be compatible with that of the target multi-damping response spectra,especially for the nuclear power plants and the buildings whose major components have the different damping ratios,which determines that employing artificial ground motion as the input ground motion of seismic analysis of nuclear power plant will be more practical and convenient.The purpose of this study is to provide a synthetic method of the artificial ground motion regarding to fit the multi-damping target response spectrum for the future seismic designs of the nuclear power plants and other major projects in China.This paper uses time-domain pulse function to adjust the the theory of the ground motion,employs the harmonic function to modify the natural ground motion in order to make it be compatible with the target multi-damping response spectrum,and improves the previous modification method in order to accelerate the convergence of the iterative process.Numerical examples show that the improved method not only has the high modify accuracy,but also preserves the basic characteristics of the original ground motion.Firstly,This paper expounds the theory and methodology of matching target response spectrum based on time domain impulse function,and dwells on the composition of the producing harmonic function and the steps of matching target response spectrum with the harmonic function.Then it explained how the conventional method can be employed to fit the multi-damped target response spectrum of nuclear power plants,and how it would become difficult to converge.The superposition method considering the positive and negative contribution of incremental harmonic time history response to the time history response of ground motion is given through theoretical derivation.The improved method eliminates the "stubborn point" of non-convergence and improves the fitting accuracy.When fitting the multi-damping target spectrum,the modification of the ground motion based on the order of relative error between the response spectrum of ground motion and target spectrum is more suitable for practical application.Numerical examples show that the fitting convergence rate can be improved by fitting the control points according to the relative error values of the control points rather than based on the order of the fixed damping values.Taking the adjustment of EI-Centro wave to match the multi-damping target spectrum of nuclear power plant as an example,the specific steps of fitting the multi-damped target spectrum of nuclear power plant and the effectiveness of the improved fitting method are described.Finally,the different "seed" ground motion are selected from the multiple groups for fitting and adjustment,and the characteristics of the adjusted ground motion are analyzed.The obtained multi-group designed ground motion are input into the bridge structure to analyze the influence of different designed ground motion on the structural response.Although the multiple groups of designed ground motions can match the same target multi-damping spectrum,their Fourier spectra are different and the more frequency components that are consistent with the natural vibration frequency of the structure,the greater the response of the structure will be.