| China is one of the most active seismic regions in the world.The earthquake disasters are characterized by high frequency,high intensity and wide distribution in China.After the Wenchuan earthquake,the bridge was seriously damaged or the residual displacement was too large to use,which caused the rescue workers and materials could not be transported to the disaster areas in time.It is missed that the best time of rescue,which was one of the reasons for the serious loss of life and property in Wenchuan earthquake.Therefore,how to reduce the damage of the bridge structure under the earthquake and reduce the residual displacement after the earthquake has become an urgent issue to be solved.The self-centering friction damper can effectively dissipate the vibration energy of the bridge under the action of earthquake and reduce the post-earthquake residual displacement.However,the current self-centering friction damper is generally based on the common friction damper by adding a reset spring.The initial pre-force of the spring is required to be greater than the maximum frictional force of the damper,so that the damper has the self-centering function.Due to the existence of frictional force,the self-centering ability of the ordinary self-centering friction damper is reduced,which affects its application and promotion in engineering.In order to improve the reset ability of the self-centering friction damper,a new type of self-centering friction damper is proposed in this paper.When the damper piston deviates from the equilibrium position,the piston is affected by the restoring force and frictional force.When the piston moves to the equilibrium position,the frictional force disappears,and the piston reset to the equilibrium position automatically under the restoring force.Due to the disappearance of frictional force during reset,the self-centering ability of the damper is improved.the expression of stiffness is solved by analytical method and the hysteretic curves is obtained by experiment.Three bridges with self-centering friction damper,lead rubber bearing and laminated rubber bearing are simulated by using the finite element software OpenSees.The advantages of the self-centering friction damper are compared and analyzed.The advantage of the damper in reducing the residual displacement after earthquake is verified by the substructure hybrid test.It is proposed that the rotational restraint effect of the superstructure on the top of the pier should be considered in the design of the damper stiffness.The main work of this paper includes the following aspects:(1)A new type of self-centering friction damper is proposed.The damper is mainly composed of reset springs,wedge-shaped sliders,friction plates and pistons.The frictional force can be changed through the relative sliding of the wedge-shaped sliders on the piston.When the damper is under tension or pressure,there is frictional force between the friction plates and the damper cylinder wall,so that it has good energy dispation capacity;when the tension or pressure of the damper is reduced,the frictional force disappears,then the self-centering ability is improved.The parameters of the damper are analyzed,and the equations are obtained that the damper parameters need to be satisfied to ensure its normal operation.(2)Based on the theory of elastic mechanics,the force acting on the damper in each working stage is analyzed,and the analytical expression of the forcedisplacement of the damper in each stage is deduced.The relationship between the damper stiffness and the damper structural parameters in each stage is obtained too,which provides the theoretical basis for the design of the damper.(3)The self-centering friction damper is made,and the test is divided into 50 working conditions according to 2 different initial preloads,5 different start sliding forces and 5 different loading rates.The hysteretic performance test is carried out to verify the correctness of the analytical solution of the stiffness of the damper.The relationship between the initial preload and the restoring force of the damper and the relationship between the test loading rate and the equivalent viscous damping coefficient are studied.(4)It is given that the installation method of the new type self-centering friction dampers of the bridge.For irregular bridges with unequal pier height,it is proposed that the pier top should be considered as free when designing the lateral damper stiffness,while the pier top should be considered as directional constraint when designing the longitudinal damper stiffness.On this basis,according to the principle that the shear force at the bottom of pier is equal and the principle that the bending moment at the bottom of pier is equal,the design formula of the damer stiffness is derived respectively.Then the design flow of the damper stiffness is given.A concrete continuous beam bridge with unequal pier height is taken as an example to verify the correctness of the proposed method.(5)Taking a 4-span continuous beam bridge as the research object,self-centering friction dampers and teflon sliding plate bearings,lead rubber bearings and laminated bearings are configured respectively.The time history analysis is carried out via OpenSees,and it is analyzed that the displacement of the pier top,the displacement of the girder,the relative displacement between the pier and the girder,and the internal force of the pier.Compared with the other two kinds of bearings,the bridge with self-centering friction damper has advantages in the aspects of pier internal force,bridge displacement and residual displacement.(6)Taking the bearing and damper as the test substructure,and the other parts of the bridge with self-centering friction damper as the numerical substructure,the substructure hybrid test is carried out.Three kinds of ground motion records are input.The differences between the finite element analysis results and the test results in the displacement,residual displacement and internal force of the pier are analyzed to verify the accuracy of the above finite element model. |
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