| Earthquakes are a common natural phenomenon,and there are about 50,000 "seismic" earthquakes in the world every year.At present,with the increase of large bridges,the importance of the study of Bridge Seismic isolation is increasingly prominent.As the weak link of the bridge structure,the bearing plays the role of load transfer and shock absorption and energy dissipation under the action of earthquake,and its importance is self-evident.Friction pendulum bearing(FPB bearing)has become a commonly used shock-absorbing and isolating device for large-scale bridges due to its excellent shock-absorbing and isolating performance and stability.The bearing uses a simple pendulum principle and several sliding surfaces to extend the structure’s freedom.The purpose of vibration period and dissipating seismic energy,and because of the special arc-shaped sliding surface of the FPB bearing,the bearing also has the ability to automatically reset and can withstand the test of many earthquakes.Taking Jingyuan Jintan Yellow River Bridge(the main bridge part)as the engineering background,this paper uses Midas civil finite element analysis software and nonlinear dynamic time history analysis method to determine the long-span FPB support parameters,the selection and optimization of wide low tower cable-stayed bridge,the seismic response analysis under different pier heights and different seismic wave conditions,and the comparative study with non-vibration-isolated supported bridges.The main contents of this paper are as follows:(1)The development and application status of shock absorption and isolation technology are introduced.The structure and working principle of FPB bearing are discussed.There are many kinds of bridge seismic response analysis,but due to the complexity of the bridge structure,In this paper,the nonlinear dynamic time history analysis method is applied to the seismic analysis of bridges by using computer software.The selection and processing of seismic wave have great influence on the dispersion of general analysis results,so this article also introduces the types and formation of seismic waves.Finally,use the bridge safety assessment report 1940,EL Centro Site,180 Deg,1952,Taft Lincoln School,339 Deg,1971,San Fernando,339 Deg these three seismic waves.(2)Briefly describe the main technical standards and key component dimensions of the engineering background,apply Midas Civil finite element analysis software,and establish a finite element model of the full bridge of the Jingyuan Jintan Yellow River Bridge according to the design specifications and drawings.(3)Using the method of linearly changing the friction coefficient and the radius of curvature,the comparative analysis is carried out from the three aspects of internal force,displacement and seismic isolation rate that characterize the seismic isolation performance of the support.The two important parameters that affect the seismic isolation performance of FPB bearings,namely the coefficient of friction and the radius of curvature,are studied.In this paper,the slow friction coefficient is 0.03,0.04,0.05,0.06,0.07,0.08,0.09,0.10,and the radius of curvature is 5m,7m,9m,11 m,13m for analysis.According to the analysis,the bending moment amplitude of the 8# pier bottom reaches the minimum When the friction coefficient is [0.05～0.06],it decreases as the radius of curvature increases.The results show that the internal force of the flexible support is more sensitive to the change of the friction coefficient,but less sensitive to the change of the radius of curvature.When the two parameters are coupled.There is no clear matching value to make the internal force,displacement,and shock absorption rate reach the best state.(4)The impact of different pier height changes on the seismic isolation performance.Considering two ways of pier height change and non-equal height change,in the study of equal height piers,the main piers of 7# and 8# changed by 10 m,15m,20 m,25m and 30 m,respectively.The results show that the use of FPB brackets and pier height changes have the effect of prolonging the structural period of the bridge structure.However,when the height of the bridge pier is high,the shock absorption and isolation performance of the FPB support will be reduced.That is,when the bridge pier is low,FPB bearings have better seismic and seismic isolation effects than non-seismic bearings,and non-seismic bearings of high-pier bridges have better seismic and seismic isolation effects than FPB bearings.In the study of non-equal height piers,the height of 7 piers remains unchanged,and the height of 8 piers changes.The results show that under different pier height conditions,the pier height will not change as the pier height changes.The bending moment at the bottom of the pier is only related to the action of seismic waves,while the bending moment at the bottom of the variable-height pier gradually increases with the increase of the pier height,but the value of the bending moment under different seismic wave conditions is not much different. |
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