Analysis Of Dynamic Characteristics And Seismic Response Of Asymmetric Special-shaped Steel Arch Bridge

The asymmetric special-shaped steel arch bridge is unique in shape and beautiful in line.Both large and small arch ribs are supported by three points.Near the middle pier,the two arch ribs are combined into one and pass through the main girder.The arch ribs and main girder are separated.The arch ribs and piers are combined.Based on this unique structural form,the force of the structure is more complicated.Under the action of an earthquake,there are often members that withstand large internal forces.These members are easily damaged,and members damage will aggravate the consequences of an earthquake disaster.Therefore,it is of great significance to analyze the dynamic characteristics and seismic response of such structural systems.In this thesis,a reasonable finite element model is established based on a two-span asymmetric special-shaped steel arch bridge to analyze the dynamic characteristics and seismic response of the arch bridge.The main contents of this thesis are as follows:(1)In this thesis,a reasonable finite element model is established based on a two-span asymmetric special-shaped steel arch bridge to analyze the dynamic characteristics of the arch bridge,considering the influence of the rise-span ratio,the number of transverse braces and the suspender spacing on the dynamic characteristics of the steel arch bridge.The fundamental frequency of the steel arch bridge structure is 0.4733 Hz,and the first-order mode of the steel arch bridge structure is the transverse symmetrical bending of the main girder,indicating that the transverse stiffness of the steel arch bridge structure is less than the longitudinal stiffness and the vertical stiffness.The dynamic characteristics of the steel arch bridge structure are mainly manifested in the transverse bending vibration,vertical bending vibration and torsional vibration of the arch rib and main girder.The high-order vibration mode is complex and accompanied by in-plane and out-of-plane coupled vibration.The steel arch bridge structure is a combined force-bearing structural system formed by arch ribs,main girder and suspension rods,with good integrity,and the arch ribs and main girder are basically the same when inplane bending vibration occurs.The torsion of the arch ribs in the second-order mode of the steel arch bridge structure indicates that the torsional stiffness of the steel arch bridge structure is small.With the decrease of the rise-span ratio,the fundamental frequency of each vibration mode is gradually increasing,and the torsional vibration mode of the arch rib is most sensitive to the change of the rise-span ratio.When the number of transverse braces is 6 to 8,and the distance between the booms is 6m,the steel arch bridge has better dynamic performance.(2)Carry out the response spectrum analysis of the steel arch bridge structure under the action of E1 earthquake,analyze the seismic displacement response and internal force response under the working conditions of one-way seismic wave input and three-way combined input.The seismic displacement response and internal force response under the action of a three-way earthquake are both greater than those under a one-way earthquake,reflecting the most unfavorable state of the structure.Therefore,the three-way combination can be directly selected when the seismic design of the structure is carried out.The seismic response is analyzed.Under the action of three-way combined ground motion,the displacement response and internal force response of the large arch L/4 and the joint arch are relatively large,indicating that the two arch rib sections are weak parts of the structure and should be paid attention to in seismic design.(3)Select reasonable seismic waves,use the linear time history method to analyze the response of the steel arch bridge structure under the E1 earthquake,and compare with the analysis result of the response spectrum method,and then analyze the response under the E2 earthquake.Finally,the influence of the change of the rise-span ratio on the seismic response is considered.The displacement response law,internal force response law and maximum position of the steel arch bridge structure under the response spectrum method and the linear time history method are the same.The displacement response and internal force response law of the steel arch bridge structure under the E2 earthquake is the same as that under the E1 earthquake,but the numerical value increases greatly.Under the combined action of permanent action and seismic wave,the maximum stress appears in the arch toe section of the large arch,and the maximum is 197.85 Mpa,which is within the elastic range of Q345 steel,indicating that the steel arch bridge has good seismic performance under the stress inspection angle.(4)The influence of traveling wave effect on the seismic response of the asymmetric special-shaped steel arch bridge is studied,and the influence of different wave speeds is discussed.The results show that under the action of longitudinal traveling waves,the longitudinal and vertical displacement peaks of the arch rib of the steel arch bridge are greatly increased,and the lateral displacement changes very little.With the change of traveling wave velocity,the change law of the displacement response of different control sections of arch ribs is not the same.At low wave speeds,the seismic displacement response of the arch rib control section will achieve a maximum value.The effect of traveling wave on the internal force is also very significant.The internal force of different control sections has different changes.Under the action of longitudinal traveling wave,the axial force of the arch rib becomes smaller and the in-plane bending moment increases significantly.Both the axial force and in-plane bending moment of the small arch ribs are greatly increased.