Analysis Of Key Factors Affecting Seismic Capacity Of Girder Bridges In Service And Research On Damping Measures

A large number of old in-service beam bridges in China have seismic hazards to varying degrees due to defects in seismic design and aging of components,which endanger traffic safety.From the investigation of the earthquake damage of the bridge,we can see that the collision effect is the main reason for exacerbating the earthquake damage of the beam bridge.In order to provide some suggestions and references for improving the seismic capacity of existing beam bridges,a finite element analysis model is established based on actual engineering,and the nonlinear time-history analysis method is used to study the key factors affecting the seismic capacity of active beam bridges and effective Bumping measures.The main research contents and conclusions are as follows:(1)According to three collision stiffness calculation theories,the collision stiffness,damping and initial clearance of the collision unit are analyzed,and the dynamic responses of the collision beam bridge and the collision-free beam bridge are compared.The results show that the parameters of the collision unit influence law of the response is different,and considering the collision effect will aggravate the seismic response of the structure.(2)Taking the lead-isolated rubber bearings and three nonlinear parameters(yield force,yield displacement,horizontal equivalent stiffness)as the research objects,the dynamic response of the isolated seismic beam bridge and the influence of parameters are analyzed.The results show that: Isolation treatment can effectively protect the lower structure,but the dynamic response of the upper structure has been enhanced.The nonlinear parameter value has a significant impact on the energy dissipation capacity of the support,the dynamic response of the pier and the collision between the joints.(3)The non-isolated and isolated beam bridges with different period ratios(0.5-1.0)were established by changing the pier height and the LRB support parameters,and the impact of the period ratio on the seismic response of the active beam bridge was studied,and The relationship between the rate of change of the cycle ratio before and after isolation and the isolation effect is discussed preliminarily.The results show that the smaller cycle is very detrimental to the structure,but the improvement of seismic resistance is more obvious after the isolation treatment.(4)For non-isolated,isolated,and periodic beam bridge structures with different cycle ratios(0.5-1.0),using inter-collision and falling beams as research indicators,the performance parameters of three shock-absorbing devices on shock absorption were studied.The effect of the effect,and summarizes the reasonable values of the parameters and the effective seismic reduction plan.The research shows that for the non-isolated beam bridge in service,the Lock-up device can strengthen the pier beam restraint and shorten the natural vibration period during strong earthquakes.Speed determines the locking effect.For the seismic isolation beam bridge in service,the reasonable setting of viscous dampers at the adjacent beams and the reasonable setting of steel strand limit cables at the abutment can achieve a certain effect of restraining and dropping the beam.For isolated beam bridges with a relatively small period,it is flawed to set the damping device only at a single position.The damping scheme using a combination of dampers and limit cables is the most effective to prevent the beam from falling at the abutment,and all viscous dampers are set.The solution of the device can comprehensively improve the seismic resistance of the structure.(5)Introduced the IDA analysis method and seismic vulnerability theory,defined four damage indicators and the value of the limit,and used the probability analysis method to analyze the seismic vulnerability of the active beam bridge whether the impact effect is considered or not.The research shows that: The regression analysis results when using spectral acceleration SA as the ground motion intensity parameter are good.Regardless of the collision effect,the analysis of the seismic resistance of the bearing deformation and the ductile deformation of the pier is more conservative;when the earthquake intensity is large,the impact of the collision effect should be considered for the analysis of the shear resistance of the pier.