Researchon Real Nonlinear Analysis Of Soft Soil Layer Site Seismic Effect

The site with soft soil layer is a common site type in coastal areas of China,as a special case of local site conditions,the influence of the ground motion is always the focus in the field of earthquake engineering.Current earthquake disaster investigation and site analysis show that the existence of weak interlayer in the soil structure has a significant effect on the seismic response of the site,so the study of the effect of soft interlayer on ground motion is of great significance to the seismic design of building structures.In this paper,a damping-based hysteretic model proposed by Shangshouping is adopted and one-dimensional real nonlinear analysis method is used to analysis the site with a weak interlayer.The effects of depth,thickness,shear wave velocity,damping ratio and dynamic shear modulus ratio of the soft soil layeron the response spectrum and the peak acceleration of the ground surface motions are studied.The results show that:1?The existence of the soft soil layer makes the acceleration amplitude of the ground changed.With the difference in the depth,thickness,shear wave velocity,damping ratio and dynamic shear modulus ratio of the soft soil layer,the ground surface peak acceleration can be increased or decreased.The peak acceleration of ground surface will increase and the effect coefficient of acceleration are not obvious with the increase of the amplitude of the input ground motion when the depth,thickness,shear wave velocity,damping ratio and dynamic shear modulus ratio of the soft soil layer are restricted.For a limited ground motion,the ground surface peak acceleration decreases with the increase of depth and thickness of the soft soil layer,increases with the increase of shear wave velocity,and increases with the change of damping ratio and dynamic shear modulus ratio.It shows that the deep soft layer has a significant damping effect on the site,with the deeper the buried depth,the larger the thickness,the smaller the shear wave velocity is,the more obvious the effect of the reduced ground motion is.2?The soft soil layer makes the characteristic period of the response spectrum of the site prolonged,the curve of long period raised and the phenomenon of multi-peak spectrum appeared,and the difference ratio between the spectrums with/out soft soil layer is far greater than the acceptable error range 20% and the ratio of the maximum response spectrum in this paper has reached 18 times.The difference curve of the site response spectrum caused by the soft soil layer increase first and then decrease with the increase of structural period,there is a characteristic period corresponding to the maximum response spectrum difference ratio.The depth,thickness,shear wave velocity,damping ratio and dynamic shear modulus ratio of the soft soil layer are the main factors that determine the intensity of the soft soil layer to the surface response spectrum,while the influence of the type of input seismic wave characteristics and the peak of the input acceleration on the response spectrum of the soft ground is not obvious.