Dynamic Performance Of The Layered Soil-pile-pier System After The Earthquake

After strong earthquakes,the stiffness degradation and residual displacement of the bridge pier will occur in the railway line,which may lead to the decrease of the traffic performance of beams.The stress level of the bridge pier under the moving train is far less than that caused by strong earthquakes.More attention should be paid to the parameters of residual stiffness,residual displacement,et al.which directly affact the runing safety performance.Therefore,the research of the post-earthquake dynamic performance of the railway piers in terms of the stiffness degradation and residual displacement has great theoretical significance and engineering application value.In this study,based on the OpenSees finite element platform,a refined finite element model of the layered soil-pile-pier system is established considering the influence of seismic waves and local site effects.The evolution behavior of the residual displacement and stiffness degradation(frequency and mode)of railway bridge pier after the earthquake loading is detailedly studied,which is based on a hollow pier with circular-end section in the Shanghai-Tong railway line.The specific research contents and conclusions are as follows:(1)Based on the existing fiber element theory and the Matlab platform,an analysis program for calculating the seismic damage index of the structure and the residual effective stiffness of the element after earthquake is compiled,and the validity is verified.(2)A seismic excitation model considering the oblique incidence of seismic waves and local site effects is established,and an analysis program is compiled for the parameter sensitivity analysis.It is consequentially unreasonable in some cases that the existing ground motion time history records are directly used as input excitation.(3)The refined model of layered soil-pile-pier system based on fiber elements is established,and the dynamic analysis during earthquakes is carried out.The influence of incident wave type,incident angle and site characteristics on the peak displacement and residual displacement of the pier during the earthquake are studied.(4)The stiffness degradation and fundamental frequency evolution of bridge piers after earthquakes are studied by using the compiled program and the OpenSees platform.The results show that after earthquakes,the bending stiffness of each element of the layered soil-pile-pier system degrades more seriously than the compressive stiffness.In addition,the serious nonlinear damage of pile foundation occurred in the zone of the pile top.The damage is mainly caused by the failure of the concrete fiber,and the upper pier is still in the linear elastic stage.Finally,a parameter sensitivity analysis is carried out for the influence of parameters on the soundness index K of the bridge pier after the earthquake.