Seismic Response Of High Pier Continuous Beam Bridge Under Long-period Ground Motion

Due to the complex terrain,bridges in Western China mostly use high piers.Such bridges have large pier body mass and long structural period,and are prone to resonance under the action of long-period ground motion,which will lead to the structural seismic response beyond the scope of its seismic design,resulting in a series of bridge seismic disasters.In order to study the response law of high pier bridge under the action of ground motion,In this paper,the dynamic characteristics of high-pier bridges are analyzed,and long period ground motion under the action of the influence of the height of pier on the internal forces of the pier bottom.Secondly,lead rubber bearing and friction pendulum bearing are introduced to analyze the isolation bridge under the action of long period ground motion.Finally,the influence of the change of the expansion joint gap,the change of the stiffness of the collision element and the change of the pier height on the collision between the beams is explored to provide a reference for the design of similar bridge types.The research contents are as follows:（1）To explore the pier height difference influence on the dynamic characteristics of the high pier bridges.Two bridge models with pier height difference and equal pier height were established in the finite element software,and the dynamic characteristics of the two models were analyzed.Research indicates: With the increase of pier height,the fundamental frequency of the structure decreases,but the high order frequency approaches gradually.The increase of pier height will lead to the decrease of stiffness,while the difference of pier height will affect the distribution of stiffness,and the bending stiffness of bridge will decrease with the increase of pier height.（2）Analyze the influence of pier height difference on the internal force of high pier bridge under the action of long period ground motion.The ground motion is input into two models in the direction of bridge + vertical and transverse + vertical respectively,and the influence of pier height difference on the internal force at the pier bottom of high pier bridge under long-period ground motion and ordinary ground motion is compared.Research indicates: The pier height difference has little effect on the internal force distribution under ordinary ground motion,while the internal force distribution is very uneven under long period ground motion;The possibility of damage of high pier bridge under far-field harmonic ground motion is greater than that of near-field pulse ground motion,and the pier height difference will make the probability of damage of bridge under near-field and far-field ground motion similar,but the harm of long-period ground motion in both far-field and near-field to high pier bridge is much greater than that of ordinary ground motion;The pier height difference will increase the axial force at the pier bottom and reduce the shear force at the pier bottom of the higher pier to a certain extent,at the same time,the bending moment of the pier bottom increases under the action of long period ground motion and decreases under the action of ordinary ground motion;The pier height difference will increase the beam displacement,and the long-period ground motion will further amplify the influence of the pier height difference on the pier top displacement,when the seismic wave is loaded in the transverse direction of the bridge,the displacement distribution will become extremely uneven,which increases with the increase of pier height and increases the probability of beam falling off.（3）To explore the expansion joint clearance,collision element stiffness and the influence of the collision of the high pier on the beam.Finite element software is used to simulate beam collision,analysis in long period ground motion under the action of expansion joint width,collision,the stiffness and the collision of high pier change beam effect.Research indicates: The increase of the expansion joint spacing can lead to collision frequency and maximum impact strength decreased;Collision element stiffness impact on the collision times smaller,but will lead to the largest collision strength increases;The increase of pier height will lead to the increase of the number of collisions between beams and the maximum collision intensity;The far-field harmonic like ground motion will further amplify the number of collisions between beams,while the large amplitude velocity pulse of near-field pulse ground motion will aggravate the collision strength between beams.（4）This paper explores the damping effect and anti-collision effect of two vibration reduction and isolation devices on high pier bridges under long-period earthquakes.Set viscous dampers and friction pendulum bearings on the bridge（non isolated bridge）respectively,and compare the pier bottom response and pier top displacement of the two kinds of vibration reduction and isolation bridges and non vibration reduction and isolation bridges under the action of long-period ground motion.The results show that the vibration reduction effect of viscous damper Bridge is better than that of FPS bridge under the action of long-period ground motion,and the difference of vibration reduction effect between them is particularly obvious in reducing displacement response,But there is no collision phenomenon;The damping effect of bridges with viscous dampers under far-field earthquake action is better than that under near-field earthquake action,while the damping effect of FPS damping bridges under near-field earthquake action is more significant,and the damping effect of FPS bearings arranged on fixed piers is better than that arranged on movable piers.