Long-span Continuous Rigid Frame Beam-arch Combination Bridge Seismic Response Analysis

Continuous rigid frame beam arch composite bridge has the characteristics of large span,large stiffness and complex structure system.In recent years,it is gradually used in railway bridges,especially in the western mountainous areas.As there are many strong earthquakes in the western region,the seismic problem of long-span continuous rigid frame beam arch composite bridge is very prominent.At present,there are few studies on the seismic response of long-span continuous rigid frame beam arch composite bridge,especially its dynamic elastic-plastic analysis.In this paper,combined with practical engineering,the seismic response law of long-span continuous rigid frame beam arch composite bridge under seismic action is studied.(1)Combined with the engineering example of Pengxi River multi line super large bridge,the calculation model of continuous rigid frame beam arch composite bridge is established by using Midas civil software.Meanwhile,the calculation model of continuous beam arch composite bridge with the same span is established,and the dynamic characteristics of two structural systems are compared and analyzed.The results show that the vertical stiffness and longitudinal stiffness of the continuous rigid frame beam arch composite bridge are greater than those of the continuous beam arch composite bridge under the same conditions.(2)The seismic response laws of arch ribs,piers and main beams of continuous rigid frame beam arch composite bridge and continuous beam arch composite bridge are studied by using response spectrum analysis method,and the stress characteristics of the two structural systems under seismic action are compared and analyzed.The results show that:(1)the in-plane bending moment of the fixed pier in the transverse tie beam of the continuous beam arch composite bridge is 2.2 times of that of the continuous rigid frame beam arch composite bridge under the earthquake action along the bridge direction,and the continuous beam arch composite bridge has higher requirements on the setting of the bending reinforcement of the pier column;(2)the out of plane bending moment of the fixed pier of the two kinds of bridge structures has little difference under the earthquake action along the bridge direction.(3)Under the action of earthquake along the bridge,the vertical deformation of arch rib and main beam will cause the side pier to produce larger axial force.(3)By using the linear time history analysis method,three synthetic seismic waves are selected to analyze the response value of the continuous rigid frame beam arch composite bridge under the three-dimensional input of seismic waves,and the linear time history analysis results are compared with the response spectrum results.The results show that: the seismic response of the bridge is closely related to the selected seismic wave,because of the discreteness of the seismic response,the internal force calculation results of the three seismic waves are different,but the response law is consistent.(4)In the linear time history analysis,it is found that under the action of a certain seismic wave,the peak value of local vibration reaches the maximum and begins to decay,but the seismic response of the structure reaches the maximum.Based on this phenomenon,this paper uses the windowing analysis method of Fourier transform to analyze the influence of seismic wave instability on the results of linear time history analysis.The results show that the deformation of the first-order rigid frame bridge pier is the main one.(5)The fiber element is used to simulate the consolidation pier and side pier,and the beam element is used to simulate other structures.The dynamic elastic-plastic model of continuous rigid frame beam arch composite bridge is obtained.In this paper,the nonlinear time history analysis method is used to study the elastic-plastic response law of continuous rigid frame beam arch composite bridge under the seismic action along the bridge direction.At the same time,considering the vertical seismic action,the axial force change of the control section is more obvious,the moment curvature curve of the section is more irregular,the plastic deformation of the section is larger,and the internal force response of the section is larger.(6)Using the elastic-plastic analysis method,the plastic deformation ability of the key section of the bridge pier and the sequence of plastic hinge of each control section are analyzed.When the seismic wave is input along the bridge direction,the displacement ductility coefficient at the tie beam of the fixed pier is the largest,and the plastic hinge is formed first at the control section;the plastic hinge is formed first at the top of the consolidated pier than at the bottom of the pier,and finally at the bottom of the side pier.At the same time,using the displacement ductility coefficient index,the higher the reinforcement ratio of the pier,the higher the yield moment and ultimate moment of the structure,but the lower the ductility of the structure.