Study On The Seismic Response Characteristics And Mitigating Measure Of Fault-crossing Cable-stayed Bridge Considering Transverse Collision Effect

Due to the strong forward directivity and strike-step effect caused by active faults,fault-crossing bridges usually suffer serious damage.Therefore,relevant domestic and foreign codes normally suggest to avoid faults.However,due to the limitation of terrain,route selection and cost,some bridges have to built across active faults.Fault movement induces large transverse relative displacement between piers and beams,which leads to violent transverse collision between beams and shear-keys.The researches on the transverse seismic collision and seismic control measure of fault-crossing cable-stayed bridges are still very weak,and therefore need to be studied urgently.In this paper,a fault-crossing cable-stayed bridge was taken as objective.The influence of different parameters of shear-keys on seismic response of the fault-crossing cable-stayed bridge was lucubrated.The damping effect of viscous dampers and E-type steel dampers with different parameters was considered.Finally,parameters of shear-keys,viscous dampers and E-type steel dampers have been suggested for the example bridges.The main research of this paper are as follows:(1)A fault-crossing cable-stayed bridge was taken as objective,two finite element numerical models of the whole bridge were established based on OpenSEES platform and SAP2000 platform.The natural vibration period of the two models have been compared to verify the rationality of the model built by OpenSEES.(2)A method of fault-crossing ground motion synthesis was introduced.By decomposing the measured ground motions,high-frequency ground motions and low-frequency pulses were obtained.Reasonable velocity pulse model and pulse parameters were selected to simulate artificial pulses.Three cross-fault ground motions were obtained by superimposing artificial pulses and high-frequency ground motions.(3)The displacement of the support,the collision force of the retainer,the curvature of the bottom of the pier and the bending moment of the bottom of the pier were selected as the research indexes,the effects of initial gap d,ultimate strength Vn and nominal displacement ?n of the shear-keys on the response of the bridge were systematically studied under the excitation of synthetic ground motions.The results show that the displacement requirement of the abutment adjacent to the fault is much larger than that of the non-adjacent fault,and the larger initial gap or the higher ultimate strength of the shear-key is needed to fully limit the displacement.Increasing the nominal displacement of the shear-key ?n can reduce the collision force of the shear-key and the curvature and bending moment of the pier bottom.(4)Maxwell model were used to simulate the mechanical behavior of viscous dampers,and the effects of damping coefficient C and velocity exponent a on the damping effect were discussed.The results show that increasing the damping coefficient C can improve the damping effect,but can significantly increase the response of pier bottom;increasing the velocity index a can reduce the damping effect,but it reduces the response of pier bottom.(5)In this paper,thehe E-type steel damper was adopted as the damping measure,and a reasonable model was selected to simulate its mechanical behavior,and the influence of its main parameters(yield force Fy,initial stiffness K1)on the seismic response of the example bridge were discussed.The results show that with the increase of the yield force Fy and the initial stiffness K1,the damping effect of the damper will be improved,which is more beneficial to the shear-keys protection,but it will increase the response of the pier bottom.