Research On Site Effect Based On Multiple Factors And Its Application

At domestic and foreign,a large number of earthquake damage studies have shown that site conditions are one of the important factors that cause significant differences in regional earthquake disasters.The study of ground motion response considering site effect provides scientific basis for engineering seismic fortification and is an important part of urban earthquake prevention and disaster reduction work.First,a site analysis model is constructed based on the borehole profile data in the study area.The frequency-dependent equivalent linearization method of effective strain interval reduction established in this paper is used to calculate the site model of the selected area.Secondly,by analyzing the effects of ground rock ground motion intensity,the cover layer thickness of the site,the equivalent shear wave velocity of the site on site effects,a multi-factor-based site effect model was established.Finally,the joint analysis of the site effect and the ground motion attenuation model is performed,and a ground motion response analysis module considering the site effect is developed based on this.The main research work and results include:1.First,the assumptions and basic theory of the one-dimensional equivalent linearization method are introduced.Based on the principle of steady-state seismic response of linear elastic layered soil,the amplification factor of the shear strain transfer function and the harmonic components of ground motion are derived.In order to obtain the structural characteristics of the amplitude and frequency of seismic wave acceleration for site seismic response analysis,a discrete fast fourier transform（FFT）signal processing module was developed for complex random ground motions.Aiming at the problem of underestimation of the high-frequency band response in the traditional equivalent linearization method,this paper uses Gaussian smoothing to fit and adjust the standardized strain spectrum curve based on the research ideas of effective strain frequency correlation,and gives the strain interval reduction based on the piecewise function,the effective strain interval reduction theory is proposed,and a frequency-dependent equivalent linearization method for effective strain interval reduction is established.In this way,the actual situation of large shear modulus and small damping ratio corresponding to the high frequency components of ground motion is fully considered.2.The ground motion measurement records of vertical stations are used to investigate the reliability and applicability of the method in this paper.According to the comparative analysis of the response of the surface and ground motion and the reliability analysis of the Fourier amplitude spectrum and magnification,it is obtained that the frequency-dependent equivalent linearization method of effective strain interval reduction proposed in this paper on hard and hard sites.The calculation results can basically reproduce the ground motion response of the actual site.The analysis results of this method on general soft soil and thick soft soil sites have obvious advantages.From the calculation results of various sites,this method improves the calculation accuracy of the high-frequency components of the ground motion,and the high-frequency amplitude and the ground surface vibration response are adjusted.3.The Xi’an area was selected as the research area.Based on the landform morphology,genetic mechanism,soil structure,and engineering geological problems,the study area was divided by three levels,and the site analysis models were constructed based on the borehole profile data and soil dynamic characteristics.Considering the influence of the strength of the ground motion and its frequency spectrum characteristics on the seismic response of the site,the input ground motion of the bedrock was determined.The frequency-dependent equivalent linearization method of effective strain interval reduction was used to analyze selected areas,and the PGA amplification factors and acceleration response spectra of various types of engineering geological areas under different ground motions were obtained through calculation and analysis.Based on this,the site effect and its statistical characteristics of five types of engineering geological areas are studied.4.Based on the research of the input ground motion peak PRA and PGA amplification factor,it is found that the two show a clear power function relationship,and the empirical fitting relationship is obtained.Based on the study of the effects of equivalent shear wave velocity and cover layer thickness on the PGA amplification factor,it is obtained that the two and the PGA amplification factor exhibit linear and polynomial relationships,respectively.Based on the empirical relationship model between single factor and site effect,a multivariate nonlinear relationship between PRA,V_se,and the cover layer thickness of the site and site effect was obtained,and a site effect model based on multiple factors was established.The site effect and the ground motion attenuation model are jointly analyzed,and the ground motion distribution of the site on the bedrock plane is calculated using the ground motion attenuation relationship.Then the ground motion distribution of the surface is obtained based on the field effect analysis of the study area.Through the joint analysis of ground motion attenuation and site amplification effects,a systematic and complete analysis method of ground motion response has been formed.Based on this method,a ground motion response analysis module considering site effects was developed,and the module was used to demonstrate the ground motion response results in a specific study area.