Study On Seismic Performance Of Rocking Bridge Piers Retrofitted With Cable-sliding Friction Aseismic Bearing

At present,the rocking bridge with the function of effectively controlling earthquake damage and self-center after earthquake become one of the research hotspots in the seismic field of Bridges.However,the connection mode of piers and beams in the existing research on rocking piers is basically consolidation.In this paper,the cable bearing is introduced on the basis of the pier beam consolidated rocking pier.the damping mechanism and seismic performance of the bridge are studied by combining theoretical derivation with finite element simulation.The main research contents and conclusions of this paper are as follows:(1)Study on the mechanism of vibration reduction of rocking pier system combined with seismic bearing.The main components of the rocking bridge pier system combined with seismic bearing are determined,and its seismic mechanism is discussed.According to the working conditions of each component under different strength earthquake,the working state of the bridge pier is divided into the non lifting stage,the rocking stage and the yielding stage of the prestressed reinforcement,and its dynamic analysis model is derived based on Lagrange equation.According to the possible failure modes of the rocking bridge pier system with cable bearings,the relevant limit states and quantitative indexes are determined.(2)The incremental dynamic time history analysis of rocking pier system with seismic bearing.In order to analyze the response of the rocking bridge pier with damping bearings under different intensity of earthquake,and to facilitate the comparison with the traditional damping system,the bearing damping system model,the traditional rocking damping system model and the rocking damping system model with damping supports are established respectively through the finite element software SAP2000,and the incremental dynamic time history analysis is carried out.It should be found that compared with the other two systems,the rocking damping system combined with damping bearings can effectively reduce the bending moment at the bottom of the pier,and effectively reduce the displacement and prestress loss at the top of the pier compared with the traditional rocking damping system.(3)The sensitivity analysis of seismic performance of rocking pier combined with seismic bearing.This paper analyzes the influence of the design parameters of prestressed reinforcement and cable damping support on the seismic performance of the swing pier system combined with damping support,which provides a reference for the selection and design of reinforcement and support.The analysis results show that with the increase of the initial tension of prestressed tendons,the pier column is less prone to swing,and the prestressed tendons are more prone to yield;too small yield strength of prestressed tendons will make the structure enter the yield stage of prestressed tendons under the design earthquake,thus reducing the lateral stiffness of pier column;increasing the number of prestressed tendons can significantly reduce the stress of reinforcement,and avoid the yield of reinforcement;the larger the yield strength of prestressed tendons is The larger the free travel of cables will increase the axial force of prestressed tendons and make it easier to yield,and the larger the free travel of cables will make the structure enter the swing stage under frequent earthquakes;the larger the yield strength and post yield stiffness of supports can not effectively reduce the inertial force of superstructure,thus increasing the axial force of prestressed tendons and making the structure easier to enter the swing and yield stage of prestressed tendons However,the bearing shear displacement decreases with the increase of cable stiffness,so the cable stiffness can be appropriately increased for the bridge with higher relative displacement requirement of pier beam.(4)Vulnerability analysis of rocking bridge pier combined with seismic bearing.40 historical ground motion records are selected from the American peer database,and a total of 1280 seismic acceleration time history curves are obtained by amplitude modulation processing,which are used as input for nonlinear time history analysis.According to the analysis results,the vulnerability curves of cable damping bearing and prestressed steel bar are drawn.When PGA reaches the design strength of 0.2g,the cable has a greater probability of yielding but will not be broken,and the prestressed reinforcement has a smaller probability of yielding but the prestress loss ratio is not more than 10%.When PGA reaches the rare earthquake strength of 0.38 g,the exceeding probability of moderate,severe and complete damage of support and prestressed reinforcement is not more than 7%.It is suggested that the mechanical parameters of cable damping support should be selected after trial calculation and comparison in design,so as to keep the cable in elastic state under seismic action as far as possible.