Study On The Effect Of Vibration Reduction And Isolation Of Friction Pendulum Bearing For Short Tower Cable-stayed Bridge

Earthquake is a kind of sudden and devastating natural disaster phenomenon,which causes serious economic losses.In recent years,the friction pendulum bearing is widely concerned by many scholars at home and abroad.The principle of the friction pendulum bearing is to separate the upper part of the bridge structure from the lower part of the structure through the energy isolation device,so as to extend the natural vibration period of the structure and friction energy dissipation mechanism to reduce and dissipate the ability of transmission to the bridge superstructure,so as to reduce the earthquake disaster of the bridge.At the same time,the friction pendulum support adopts a certain arc curved surface structure,so the friction pendulum support has the ability of self reset.This paper is based on the construction of Jingyuan Jintan Yellow River Bridge(100 + 168 + 100)m project,using Midas Civil analysis software uses the method of theoretical research and numerical simulation to analyze the specific damping situation of low tower cable-stayed bridge with friction pendulum bearing,uses the nonlinear dynamic time history analysis method to study the specific damping ratio when the bearing is arranged in different ways,finds out the vibration reduction and isolation situation of movable bearing and fixed bearing in the elastic range of the pier,and changes the main parameters of the bearing.The main contents of this paper are as follows:(1)Consulting relevant documents,discussing common bridge seismic isolation bearings,and introducing the composition of friction pendulum fixed bearings and friction pendulum movable bearings.Based on the construction of Jingyuan Jin Tan Yellow River Bridge(100+168+100)m,the engineering background is described in detail.According to the engineering site background and seismic safety assessment report,three seismic waves are selected,namely El Centro wave,Taft wave and San Fernando wave,and the analysis method of bridge seismic response is determined.The irregular continuous bridge based on friction pendulum bearings adopts time-history analysis method.(2)The finite element model is established,the pile foundation is simulated by “m” method,and the arrangement of bearing is introduced.According to the natural frequency of the structure,it is analyzed that the base period of the structure can be effectively extended by the friction pendulum isolation bearing structure,and compared with the non damping isolation structure,the internal force of the pier body is reduced.For the seismic response,three evaluation indexes are selected: the maximum bending moment at the bottom of the pier,the maximum shear force at the bottom of the pier and the displacement at the top of the pier.As far as the movable bearing pier is concerned,its longitudinal vibration reduction rate is obviously better than that of the transverse direction.Further summing up the internal forces of all piers and the displacement of pier top,it is found that the average vibration reduction rate along the bridge direction is about 80%,while the internal force vibration reduction rate along the bridge direction is about 36%,but the lateral displacement of the bridge is larger than that of the non reduced isolation structure,so the vibration reduction and isolation situation along the bridge direction is obviously better than that of the transverse bridge direction;(3)Two influencing factors of friction pendulum bearing are studied: friction coefficient and bearing curvature radius on seismic response of beam structure of low-pylon cable-stayed bridge.The friction coefficient is 0.07,0.06,0.05,0.04,0.03.The bearing curvature radius of main pier is 7m,7.5m,8m,8.5m,9m,9.5m,10 m,10.5m,11 m.The corresponding bearing curvature radius of secondary pier is 3m,3.5 m,4m,4.5m,5m,5.5m,6m,6.5m,7m;Combined with the theoretical hysteretic curve of the friction pendulum bearing,the results show that different friction coefficients have obvious damping effect on the bridge.The damping effect is not very sensitive to different bearing curvature radii.When the friction coefficients are between [0.03 and 0.05],the isolation rate increases with the increase of the friction coefficient.When the friction coefficients are between [0.05 and 0.07],the isolation rate decreases with the increase of the friction coefficient.(4)The multi-objective optimization method is used to optimize and summarize the friction coefficient and curvature radius of the friction pendulum bearing.The results show that the variation trend of the amplitude of dynamic response to the curvature radius and friction coefficient of the friction pendulum bearing under different earthquakes is different,which cannot minimize the bending moment at the bottom of the main pier,the shear force at the bottom of the pier and the displacement at the top of the pier at the same time.