Study On The Reasonable Restraint System Of Curved Bridges Under Ground Motions

Curved bridge is widely used in bridge construction with its good adaptability and aesthetic feature,and plays an important role in the transportation network.However,due to the special geometrical structure of curved bridge,its mechanical characteristics are much complicated leading increased damage risk in the circumstance of earthquake.There are cases show that varying degrees of damages could occur in the curved bridge by the destructive earthquake.By analyzing seismic damages of curved bridge among a large number of cases,it can be found that the arrangements of the bearings and the movement limiting devices are the key factors affecting the seismic response of curved bridge.Therefore,setting reasonable analysis models for the bearings and the movement limiting devices is the basis of the seismic performance analysis of a curved bridge.In view of this,the seismic response and the design of the reasonable restraint system of the curved bridges are further studied herein after investigating the mechanical properties of the restraint system,which consisting of bearings and movement limiting devices,with combination of experiments and numerical calculations.The main research and achievements are as follows:1.The seismic damages of several curved bridges with different restraint systems occurred in Wenchuan earthquake were summarized herein.The nonlinear time-history method was used to compare and analyze the seismic response of curved bridges with different restraint system and the stress state of main components under different horizontal ground motions.Then the transmission mechanism and energy dissipation mechanism of curved bridges with different restraint systems were discussed to interpret the mechanism of seismic damage of curved bridges.2.The experimental studies on the mechanical properties of laminated elastomeric bearings were carried out herein.The laminated elastomeric bearings without top and bottom plates were taken as the object to conduct the quasi-static experiment of the cyclic large displacement of the unbonded laminated elastomeric bearings.The test results showed that the mechanical deformation performance of laminated elastomeric bearing was mainly divided into 3 types,of which were pure shearing deformation,roll-off at top and bottom surfaces and friction sliding.The mechanical properties of the bearing after friction sliding showed a stable force-displacement hysteresis relation,and the frictional sliding characteristic of the bearing could play the role of fuse element,which is advantageous to reduce the seismic force transferred to the substructure.An analysis model for laminated elastomeric bearings that could reasonably reflect the force characteristics before and after the sliding of the bearings was proposed.3.The failure test of horizontal cyclic loading of concrete shear keys were carried out herein.The failure modes of concrete shear keys with different design parameters were compared to analyze the influence of different design parameters on the horizontal bearing capacity,stiffness and ductility of concrete shear keys.An analysis model of shear keys that could reasonably reflect the motion constraint ability of shear keys under earthquake was proposed.4.The influence of different restraint system analysis models on the seismic response of curved bridges was studied.The results showed that,the finite element analysis model of the curved bridges with the restraint system analysis model proposed herein could better reflect the structural earthquake damage phenomenon and the stress state of main components,while neglecting the damage of the restraint system could cause underestimation on the displacement of the superstructure and overestimation on the seismic force of the substructure.The restraint system analysis model proposed herein is thus recommended in the seismic analysis of bridges.5.With respect to the phenomenon of the bidirectional collision between the main girder and the radial abutment and tangential shear keys,the seismic response of curved bridges under different collision modes was analyzed and compared with the results of the equivalent straight bridge.It is found that the collision effect is the main reason for the rotation of the main girder,and the collision effects in two directions will affect each other.The collision mechanism of the curved bridges is thus interpreted.6.The influences of structural parameters on seismic response of curved bridges were analyzed to propose the design parameters of the reasonable restraint system of curved bridges.Based on the restraint system analysis model proposed herein and the influence of nonlinear collision effect,the finite element analysis model of curved bridges with different restraint systems was established.By analyzing the influences of curvature radius,pier height arrangement,span length and span number on seismic response of curved bridges with different restraint systems,the variation law of the seismic response of curved bridges under different parameters was obtained,and the design parameters of the reasonable restraint system of curved bridges were proposed.By using Tornado graphic method,the sensitivity analysis of seismic demand of curved bridges was conduct to sort out influence degrees of different structural parameters,whereby the parameters significantly influencing on structural earthquake demand were found.7.The seismic vulnerability of curved bridges with different restraint systems was studied based on probabilistic seismic demand analysis(PSDA)method.According to the test results,the limit failure state of different components was defined.Based on the regression analysis,the probabilistic seismic demand model of the component was obtained.Then,the component and system curves of the curved bridges with different restraint systems were established.The vulnerability of curved bridges with different restraint systems under different damage states was derived.The seismic performance differences of curved bridges with different restraint systems were discussed to comprehensively evaluate the influence of restraint system on the seismic behavior of curved bridges.