Research On Calculation Method Of Predominant Period Of Seismic Site Major:Geotechnical Engineering

Forced resonance is the main reason for the damage caused by the self vibration of the tall building,which is the main reason for the damage in the earthquake process.It can accurately estimate the site predominant period,provide reference for the early design of the building,and can effectively reduce the occurrence of the earthquake damage in the tall buildings.The traditional method of site predominant period calculation is affected by the degree of site model simplification,and the calculation accuracy is often limited because of the different calculation method,model size and grid size.In order to overcome the shortcomings of the time domain numerical algorithm,this paper proposes a more efficient and intuitive algorithm of site predominant period,harmonic excitation spectrum method,based on the principle of interface wavelet.In this paper,the free wave field of the site is simplified as one dimensional wave problem in the elastic layer half space model.According to the principle of the interfacial wavelet,combined with the theoretical seismogram synthesis method in the layered homogeneous medium,the simple harmonic waves of different periods are taken as the incident seismic waves,and the convolution operation is carried out respectively with the field pulses,and the different periodic simplification is obtained.The seismic response is caused by the harmonic,and the maximum response value of the site is obtained by the periodic harmonic waves.The period of each order of the site corresponds to the maximum of the harmonic excitation spectrum,and the excellent period of the site is selected accordingly.This paper proves that the method has the advantages of high calculation efficiency,accurate result and good reliability by compiling Matlab software program and engineering example,and further discusses the factors such as cover layer thickness,soft and hard interlayer position,soft and hard degree of bedrock,seismic wave incidence angle and so on.For the impact of the site's excellent cycle,we get the following understandings:(1)By comparing the effect of different factors on the site excellence cycle,it is found that the site predominant period is most affected by the cover layer,which is manifested by the increase of the site predominant period value with the increase of the thickness of the covering layer,and the soil cover layer thickness is within the range of 10-20m,and the variation of the site predominant period with the thickness is smaller.When the cover layer is greater than 30m,the site predominant period T is obviously influenced by the thickness of the soil cover layer,and it changes with the thickness of the layer.It can be seen clearly that the influence range of the site's remarkable period on the site reaction increases with the increase of the site thickness.(2)The appearance of interlayer and interlayer in the actual engineering site increases the site remarkable cycle obviously,and the influence of the soft intercalation is more obvious than that of the hard interlayer,and the increase of the buried depth of the soft intercalation makes the site predominant period value increase,while the hard interlayer is more shallow in the sequence of the site section.The longer the position is,the longer the natural vibration period of the site is.(3)In this paper,by changing the parameters of the rock wave impedance,the s predominant period of the site considering the influence of the bedrock is calculated,and the influence of the bedrock on the natural vibration characteristics of the site is studied.The study shows that,although the deformation property of the base rock does not affect the value of the predominant period of the site,it has increased its influence range,which has an adverse effect on the predominant period of the design building.(4)This paper also makes a preliminary exploration of the application of the two-dimensional model of harmonic excitation spectrum method.It is found that the predominant period of the inclined incident site of the seismic wave has some influence.In a certain range,with the increase of the incidence angle,the predominant period of the site gradually becomes smaller and the angle of the incident angle is less than 15 degrees.When the incidence angle is greater than 15 degree angle,the reduction of the dominant period will increase and the predominant period value will decrease obviously.It is found that with the increase of the angle of incidence,the impulse response of each order gradually decreases with the increase of the incidence angle,and the influence time of the excellent period decreases,that is,the waveform of the horizontal pulse time graph becomes "short" and "thin" gradually.