Study On Displacement Response Spectra Of Ground Motions And Development Of Seismic Design Spectra

Seismic damages indicate that using displacement parameter to measure the state of structure subjected to earthquake is more reasonable,and thus,the concept of displacement-based seismic design method is gradually formed.At present,the domestic and international scholars generally believe that the displacement-based seismic design method is one of the most effective way to realize the performance-based seismic design theory.As the important role of the acceleration design spectrum to the force-based seismic design method,the displacement design spectrum is one of the major contents of the displacement-based seismic design method.Using several factors which could significantly influence the displacement response spectra as the starting point,this paper systematically investigates the characteristics of the displacement response spectra and provides a set of parameters of determining the displacement design spectra based on the ground motions selected from 2780 worldwide stations of 207 earthquakes.To apply in the traditional force-based seismic design method,the acceleration response spectrum is also investigated during the analysis of the displacement response spectrum.This paper mainly contains the following several research contents:(1)Ground motion processing is one of the important issues that should be considered in the research work about ground motion response spectra.The filtering cut-off period is one of the key parameters in ground motion processing.The effects of the filtering cut-off period on the acceleration response spectrum can be neglected,however,the effects on the displacement response spectrum are significant.To obtain accurate and effective ground motion spectral displacements and statistical results,this paper uses the wavelet multi-scale analysis to analyze the long-period noise and proposes a quantitive method of determining the high-pass filtering cut-off period and compares it with several previous proposed methods.(2)Pulse-like ground motions usually have high peak ground velocity and displacement,and the spectral displacements are significantly greater than the spectral displacements of ordinary ground motions.To improve the seismic safety level of the structures located in near-fault region,the displacement response spectral characteristics of pulse-like ground motions should be considered in the calibration of displacement design spectra.Besides,to eliminate the influence of this type motion on the analysis results of non-pulse-like ground motions,this type motion should be selected out.To eliminate the subjective factor of the selection of pulse-like motions,this paper proposes a quantitative method to identify pulse-like motions and compares the method with several previous proposed methods.(3)For the convenience of the application in the traditional force-based seismic design,a design spectral form in which the spectral displacements are in curve form in long periods and the spectral displacements and spectral accelerations can be covert to each other is proposed in this paper based on the design spectra of Eurocode.This paper uses the proposed processing method to process the ground motions selected in this study and adopts the proposed identification method to identify pulse-like ground motions.The effects of earthquake magnitude,soil condition and distance on ground motion response spectra are then systematically discussed.The design spectral parameters for non-pulse-like ground motion and pulse-like ground motions are provided respectively.To discuss the effectiveness of the design spectral method and design spectral parameters,the design spectra of this paper,the design spectra of Chinese code,American code and European are compared.(4)The spectral characteristic of pulse-like ground motions is significantly different with that of non-pule-like ground motions.However,the influence of this type of motion is hardly considered in the seismic design of structures by traditional design spectral method.Moreover,the regression relation of pulse period to earthquake magnitude proposed by previous studies cannot be incorporated in the traditional design spectrum.To enhance the ability of structures located in near-fault zone to earthquakes,it is highly needed to consider the influence of this type of motion.In view of this,this paper proposes a method of deriving design spectrum in which the spectral shape and value could have reasonable changes according to the frequency content of ground motions based on the properties of the ground motion components obtained by the wavele multi-scale method.