The Seismic Response Analysis And Seismic Isolation Research Of Continuous Beam Bridges With High And Low Piers In Mountain Areas

Since the 21st century,China has implemented the great strategy of developing the western region,realizing the rapid development of transportation in the western and southwestern regions,and has also made a leap-forward development in the bridge infrastructure in the western and southwestern regions of China.However,most of the terrain in the western and southwestern regions are hilly mountains,and they are located in high-intensity areas and earthquake-prone areas.These complex terrains,environments and other factors have brought enormous challenges to the seismic design of bridge design.Based on a specific project in Tibet,this paper uses Midas Civil software to model,calculate and analyze the seismic force distribution of high pier bridges,low pier bridges and high and low pier hybrid bridges;explore the relationship between seismic force distribution and pier stiffness,propose the reasonable range of specific values for the stiffness ratio of continuous bridge piers.Finally,the applicable height of the seismic isolation design for the equal pier height bridges is studied.The main research contents and results are as follows:Firstly,by using Midas Civil software to model,calculate and analyze the high pier,low pier,high and low mixed pier bridge model under different boundary conditions,it is concluded that under the x+z seismic input,the distribution of the seismic force of the pier and the combined thrust stiffness of the pier are basically positively correlated.The low pier with relatively large stiffness bears most of the seismic action;Under the y+z seismic input,the seismic force distribution of the pier and the combined thrust stiffness of the pier are generally inversely related linearly.The high pier with relatively low stiffness is subjected to most of the seismic action;The low-rise bridges can reduce the seismic force of each pier by using the seismic isolation bearings.However,as the height of the piers increases,the reduction will be smaller and smaller.Secondly,by using Midas Civil software to study the internal force of the pier bottom and displacement when the height of the intermediate pier is changed and the pier height of the other piers is constant,it is concluded that when the stiffness ratio of adjacent piers is less than 0.5,the bending moment tends to concentrate on the higher piers.When the stiffness ratio of adjacent piers is greater than 2.0,although the bending moment distribution of the adjacent piers tends to be average,the higher and softer piers will produce larger relative displacements of the top and bottom.Therefore,it is recommended that the reasonable ratio of the stiffness ratio of adjacent piers is 0.5~2.0.Thirdly,by using Midas Civil software to analyze the seismic force and displacement of the continuous beam bridge with the same height of the same bridge pier,it is concluded that when the ratio of the anti-push stiffness of the combination of piers of the seismic isolation bearing and the traditional support is less than 0.9,The lead-separated rubber bearing can reduce the seismic force and the displacement of the pier top of the bridge pier by more than 10%.Therefore,it can be considered that the seismic isolation bearing is suitable,and then according to the calculation method of the anti-push stiffness of the bridge pier and the combined thrust stiffness,the critical pier height applicable to the seismic isolation design can be derived to guide the design of the actual project.