Research On Mechanical Performance And Optimal Design Of Pile Cap Of Large Tonnage Swivel Bridge

At present,China’s highway,railway and urban rail transit are in and will continue to be in a stage of rapid development.The density of the road network is increasing quickly,and the problem of line intersection is inevitably faced in route planning.Swivel bridge is widely used in the construction of three-dimensional crossing traffic line because of safety,speed,and ability to minimize interference to existing lines.As the key forced member of the swivel bridge,the cap plays a vital role in the safety of the bridge during the construction phase and the operational phase.With the development of swivel technology,the tonnage and span of swivel bridges continue to break through records,which puts forward higher requirements for the design of the caps.However,the relevant codes have no provisions specifically for the design of the bearing capacity of the swivel cap.The design of cap of the built project is often conservative,the thickness is too large,and leads to the increase of the excavation depth of the foundation pit,which not only increases the amount of support work,but may also cause greater risk of disturbance to existing lines.Based on the engineering background of the Xixi Swivel Bridge of the new Fuzhou-Xiamen Railway,this paper studies the mechanism of the force transmission of the swivel cap and its influencing factors,and analyzes the force of the entire process of the rotation of the cap.On the basis,optimal design of the cap is conducted to find a reasonable design method for the thickness of the cap.The main work done is as follows:(1)The software Ansys is used to establish the finite element model of the swivel cap.The force transmission mechanism of the swivel cap is revealed by analyzing the transmission path of the principal compressive stress,the numerical calculation result of the bearing capacity is compared with the calculation results of the national standard formula.In addition,the influence of the bridge pier form,pitch-thickness ratio of pier(pier spacing/pier width),spherical hinge spherical radius,spherical hinge base form and pile arrangement form on the force of key parts of the cap is studied.(2)The force status of the cap before the rotation and the uniform rotation stage is compared and analyzed.The influence of angular acceleration on the force performance of the cap during the acceleration rotation stage is studied and the angular acceleration limit is obtained.According to the unbalanced moment measured in the on-site weighing test,the force status of cap under the action of symmetrical load and eccentric load is compared and analyzed,and the effect of the unbalanced load on the stress of the cap in the accelerated rotation stage is studied and the unbalanced load limit is obtained.(3)Based on the study of the force transmission mechanism of the swivel cap and the influencing factors of its force performance,different measures to reduce the thickness of the cap are proposed,and the force analysis of the entire process of the swivel is carried out to obtain the optimization effect of the thickness of the cap under different conditions.