Research On Seismic Performance Of The Simply Supported Girder Bridge With Separated Shock Absorber-Movable Support

With the rapid development of High-Speed Railway(HSR)construction and the growing proportion of bridges in the HSR lines,the seismic performance of bridges located in high-intensity earthquake zones has got increasing attention in recent years.At present,the seismic isolation technologies have become an important way to improve the seismic performance of bridges in high-intensity earthquake zones,one of which is the shock absorber.Based on the bearing functional separation design concept,the single cantilever shock absorber has simple structure,clear energy dissipation mechanism,and superior aseismic performance.It has been already applied in railway bridges at present.Given the shortages of single cantilever shock absorber,for instance,the existence of force weakness,inconvenience to install and replace,a novel shock absorber named separated shock absorber(SSA)is proposed in this paper.First,theoretical and experimental analysis as well as numerical simulation of the SSA are done.Secondly,the aseismic performance of the separated shock absorber-movable support(SSA-MS)and its influencing factors are systematically studied.In addition,the seismic pounding responses of simply supported girder bridge with SSA-MS are analyzed.Finally,the research on the seismic fragility of simply supported girder bridge with SSA-MS is carried out.The main contents and contributions of this dissertation are as follows:(1).Research on simplified analysis method and mechanical properties of the separated shock absorberBased on the study of the single cantilever shock absorber,the structure of SSA is proposed,and the theoretical formulas of its kernel mechanical property parameters are deduced.The first batch quasi-static tests with reciprocating loads were conducted on two groups of full-scale SSA specimens with different construction parameters,based on which the seismic performance parameters of the first batch SSA,such as hysteresis property,skeleton curve,and equivalent viscous damping ratio,ductility are emphatically analyzed,and the laws of stiffness degradation and strength degradation are also studied.In addition,the hysterical properties of SSA under reciprocating load are simulated by the finite element method software ABAQUS and compared with the results of theoretical calculation and tests.The results indicate that the theoretical formulas are correct and the numerical simulation method is reasonable.(2)Analysis method and quasi-static test of the separated shock absorber considering the effect of geometric nonlinearityIn order to maximize the energy dissipation capacity of the separated shock absorber,an changed form of energy dissipation segment diameter is proposed considering the effect of geometrical nonlinearity.The second batch quasi-static tests of two full-scale SSA specimens groups with two kinds of materials were implemented to investigate the mechanical properties of the second batch separated shock absorber.The seismic performance parameters,such as hysteresis property,skeleton curve,and equivalent viscous damping ratio are analyzed.Besides,the nonlinear stiffness and influencing factors are studied.Additionally,the hysteresis properties of a single improved SSA and two SSA groups are analyzed by means of numerical simulation with ABAQUS.The simulation results show that the superposition relationship of hysteresis properties between SSA groups and a single SSA is linear,which provids evidence for the study of aseismic performance of SSA.(3)Research on the aseismic performance and its influencing factors of the separated shock absorber-movable supportAtwo-degrees-of-freedom(TDOF)mechanical model of the shock absorber simply-supported bridge is established,and the approximate formulas for the vibration characteristics and seismic responses of the TDOF mechanical model are obtained.The results of the approximate formulas and those from numerical simulation using ANSYS are compared,and the results show that the TODF mechanical model can accurately calculate the seismic response of simply supported grider bridge with shock absorber.Based on OpenSees,an object-oriented and open source software framework,a precise three-dimensional finite element model(3D FEM)of a 5×48 m simply supported girder bridge with SSA-MS is established to study the aseismic performance of SSA-MS in longitudinal and transverse directions.On the other hand,a single pier model is established to investigate the influence of mechanical property parameters of SSA-MS(such as SSA's yield strength,post-yield stiffness,MS's friction factor),the bridge structure characteristics,and the earthquake intensity on the aseismic performance of SSA-MS.(4)Research on seismic pounding responses of simply supported girder bridge with separated shock absorber-movable supportSince the beam displacement would increase after applying the SSA-MS,the seismic pounding responses of simply supported girder bridge with SSA-MS in the longitudinal direction are studied.The method used to generate multi-support seismic excitation is introduced,with the simulated analysis program is compiled by MATLAB.The FEM considering pounding effect is built up by OpenSees.What is more,the nonlinear seismic pounding responses of simply supported girder bridge with SSA-MS are investigated under three different cases:considering only the partial coherence effect,considering only the traveling wave effect,and considering both of the partial coherence effect and the traveling wave effect,respectively.Moreover,the FEM considering pounding effect is applied to study the seismic pounding responses of simply supported girder bridge with SSA-MS under uniform excitation,and non-uniform excitation considering the traveling wave effect.(5)Seismic fragility of simply supported girder bridge with separated shock absorber-movable support considering various sources of uncertaintyBased on the simply supported girder bridge with SSA-MS on the passenger line,considering the uncertainty of bridge structure parameters and SSA-MS mechanical property parameters,the Latin Hypercube Sampling(LHS)method is applied to set up the bridge sample database.Combined with the far-fault ground motions and near-fault ground motions,the far-fault ground motions-bridge sample database and near-fault ground motions-bridge sample database are set up,respectively.Moreover,the damage indexes of the pier,the SSA,the MS,and the abutment are analyzed.In addition,the seismic fragility of simply supported girder bridge with SSA-MS under far-fault ground motions,and near ground motions are investigated and compared through 3D finite element models.Based on the first order boundary method,the fragility of the bridge system is established,and the seismic performance of the bridge structures is evaluated.Furthermore,the influence of pier height,pounding effect and abutment on the seismic fragility of bridge members and bridge system are studied under near-fault ground motions.