Seismic Isolation Analysis And Collision Study Of Urban Curved Beam Bridge Based On The Ratio Of Capacity To Demand

The curved beam bridge is an important type of bridge in modern traffic engineering,especially the ramp design is most widely used in urban interchange system.The curved beam bridge has the irregular characteristics of alignment,mass and stiffness distribution,and the site condition,bearing arrangement and seismic wave input of the bridge have great influence on the seismic response.In addition,the pier will produce very large plastic deformation under strong earthquakes,so that the upper structure will appear collision and separation in longitudinal direction and large displacement in transverse direction.As to the curved beam bridge,because of the influence of the coupling effect of bending and torsion,the collision and deformation of the beam are more complicated,and even the damage of collision and falling beam will appear.In this paper,a curved ramp on an overpass is taken as the engineering background,and the design concept of finite ductility structure for piers,and the parametric index of capacity demand ratio is used to evaluate the capacity of the pier.On the basis of this,the degree of the beam collision under strong earthquake and the effect of the collision on the other parts of the bridge when adopting seismic isolation bearings are studied.In the course of the study,the performance-based seismic design concept and the code for seismic design of bridges are analyzed,and the three eigenvalues(crack bending moment,equivalent moment,limit moment)in the relation of bending moment-curvature are respectively used as the parameterization index of three kinds of target properties,which are not bad,repairable and not inverted.Taking the actual maximum bending moment of piers under the E2 earthquake as the demand value,the capability Evaluation Index is introduced to reflect the safety degree of seismic design of concrete piers directly.In this paper,a nonlinear finite element model is established for the four-curve continuous beam bridge on the NE ramp of the city overpass city in Lhasa.The bending moment relationship of each column is calculated.The difference of the maximum bending moment and shear force,capacity demand ratio of bending moment,the isolation rate of bending moment and shear force,and the displacement of seismic isolation support are analyzed separately when using ordinary pot rubber bearings and friction pendulum isolation bearing.By setting the individual and two collision units separately in each expansion joint,the collision unit parameters are given with reference to the latest relevant research results,to discuss the extent of the plane twist,and the effect on piers moment,shear force and the isolation bearing caused by collision,and draw the following main conclusions.When the ordinary type of rubber bearing is adopted,the longitudinal bending moment and shear force of the bridge pier are mainly concentrated on the fixed pier.As a result,the longitudinal bending resistance of the fixed pier is seriously insufficient,and the longitudinal bending resistance of the other piers are surplus large and the seismic design is unreasonable.The distribution of transverse bridge bending moment is more reasonable,and most of the bridge transverse bridge are lack of seismic capacity.With friction pendulum isolation bearing,on the one hand bridge piers’ bending moment,shear force demand of longitudinal direction and transverse direction decreased significantly,the effect of isolation is obvious;On the other hand,the piers’ bending moment,shear distribution along the longitudinal direction is more reasonable.the bending moment and shear force demand of the bridge slightly decreased after considering the collision effect,this is because the collision limits the beam displacement under the action of the earthquake.The displacements of the isolation bearings decline after considering the collision.