Study On Static And Dynamic Performance Of Long Span Rigid Frame Cable-stayed Bridge

In the past,cable-stayed bridges with rigid frame system were mostly built in China,but mainly with medium and small span or single tower and single span.In recent years,with the increase of cable-stayed bridges in mountainous areas,cable-stayed bridges with long span and three span rigid frame system have been gradually applied.Because the main beam of rigid frame system is rigidly connected at the root of the tower,the axial deformation of the mid-span main beam is caused by temperature and concrete shrinkage and creep,with will be limited by the main tower pier and will cause additional internal forces of the structure.In-deth research on the static and dynamic performance of this bridge is of practical value for popularization and application.Based on the Bai Sha Yangtze River Bridge(200m + 520 m + 200m)in Lu Zhou City,this paper mainly completes the following research work:(1)With the help of bridge professional software,the calculation model of the full bridge spatial beam element is established.To analyze the influence of the structural system on the static and dynamic performance.The calculation models of semi floating system and floating system cable-stayed bridge with the same parameters are established on the basis of relying on the project.(2)Firstly,the force and deformation of three structural systems under live load effect are studied,and the main conclusions are drawn.The displacement of the tower top along the bridge direction and the vertical disturbance of the main beam of the rigid frame system can be reduced.And the value is basically the same as the semifloating system cable-stayed bridge.The bending moment at the top and bottom of the main pier increases significantly.But for the bending moment at the top and bottom of the main pier,the increase is obvious.With the braking force,the displacement along the bridge direction of the tower,beam and pier of the rigid frame system is greatly reduced.(3)Under the action of vehicle live load and braking force,by comparing the cable forces of three types of cable-stayed bridges,it is found that,rigid frame system,which has the least cable force.The results show that the rigid frame system can improve the fatigue performance of the cable,especially the short cable near the bridge tower Fatigue performance.(4)The internal force response and deformation response of three types of cablestayed bridges under the effect of overall temperature difference of main girder are analyzed and compared.The conclusions are as follows,under the effect of overall temperature difference,the pier top longitudinal disturbance and the main beam vertical disturbance of the rigid frame system will increase.The bending moment,shear force and axial force of the main tower pier increase obviously.This paper discusses the law of the change of the main pier force with the stiffness of the single pier.It is concluded that as the rigidity of the main pier decreases,the horizontal force at the top of the main pier and the bending moment at the bottom of the pier decrease.(5)The influence of concrete creep on the force and deformation of three different structural systems of the bridge is analyzed,creep has a greater impact on the internal forces of the main tower piers and main beams of the rigid frame cable-stayed bridge.Which will cause the axial force of the middle span main girder to increase significantly,and the internal force of the main pylon pier also increases significantly.But the vertical disturbance of the main girder caused by the creep of the rigid frame cable-stayed bridge decreases significantly.(6)The natural vibration characteristics of cable-stayed bridges with three different structural systems are calculated,the results show that the stiffness along the bridge direction of the rigid frame system cable-stayed bridge is significantly improved,but the transverse stiffness changes little when the tower beam pier consolidation is adopted.(7)The seismic response characteristics of cable-stayed bridges with three different structural systems are analyzed by response spectrum method and time history analysis method.The analysis results show that under the action of earthquake along the bridge direction,the deformation of tower top and beam end along the bridge direction of firm frame system can be reduced to a certain extent.However,the longitudinal internal force of the main tower pier has been greatly increased,especially the main pier has a large increase in internal force along the bridge.Under the cross-bridge earthquake,due to low lateral rigidity of the main tower,the lateral disturbance at the top is very large.The lateral seismic force of the main tower of rigid frame system increases,however,there is little difference between the seismic lateral force of the main pier and that of the semi floating and floating systems.