Structure Static Characteristics Analysis Of Long Span Suspension Bridge With Double Main Cable

Suspension bridges are the preferred structural form of general long-span bridges because of their superior mechanical performance.However,triple-tower twin-span suspension bridges are rarely seen in practical engineering applications.The main reason is the stiffness problem of the middle tower of the triple-tower twin-span suspension bridge:the flexible main tower can not effectively guarantee the vertical stiffness of the bridge.But with the rigid tower,the main tower will bear a lot of internal forces.If the double-cable structure is adopted in the triple-tower twin-span suspension bridge,the displacement along the bridge at the top of middle tower can be effectively restrained,thereby improving the vertical stiffness of main beam of the suspension bridge and reducing the internal force of the main tower.The suspension bridge with double main cable is still in the theoretical stage,so it is necessary to carry out detailed force analysis on it.This paper deeply studies its force characteristics from static aspects.Detailed research content includes:(1)Investigating the relevant information of the suspension bridge,summarizing the development status of the modern suspension bridge,and introducing the system of multi-span suspension bridge and suspension bridge with double main cable and its research status.The problems existing in the suspension bridge with double main cable are discussed,and the research contents and technical routes to be carried out in this paper are determined.(2)According to the bridge analysis theory of the traditional suspension bridge,the calculation formula of the internal force distribution of the main cable of the suspension bridge with double main cable is deduced,and compared with the results of finite analysis,the correctness of the formula is verified.The theory of automatic distribution of internal force of main cable is proposed which combines with the idea of equivalent load,carrying out the bridge-finishing analysis of suspension bridge with double main cable.The results show that it is feasible to use this idea to analyze suspension bridge with double main cable.It lays the foundation for subsequent research.(3)A single-span suspension bridge with double main cable model with a main span of 1800m is established,considering the action of the train live load,vehicle live load and cross wind to study the variation of the force and deformation by changing the ratio of the lower cable sag to the upper cable sag,the ratio of the internal force of the upper sling to the internal force of the lower sling and the ratio of the sectional area of upper cable to the sectional area of lower cable.By comparing the results with the traditional suspension bridg,the results show that the appropriate increase of the above parameters can improve the vertical stiffness of suspension bridge to some extent,but it will slightly increase the lateral deformation of the main beam,and will greatly reduce the torsional stiffness of the main beam.(4)A triple-tower twin-span suspension bridge with double main cable model with the main span of 1800m+1800m is established,considering the action of the train live load,vehicle live load and cross wind to study the variation of the force and deformation by changing the ratio of the lower cable sag to the upper cable sag,the ratio of the internal force,the ratio of the sectional area of upper cable to the sectional area of lower cable and relative stiffness of the middle tower.By comparing the results with the traditional suspension bridge,the results show that increasing the sag ratio can significantly improve the vertical stiffness of the main beam,increase the initial internal force ratio and the stiffness of the middle tower can improve the vertical stiffness of the main beam to a certain extent,and increase the sectional area ratio will lead to the stiffness of main beam increase first and then lead to reduction.The above parameters have a slight influence on the lateral deformation and have a great influence on the torsional stiffness of the main beam.(5)By comparing the deformation and internal force of the optimized triple-tower twin-span suspension bridge with double main cable with the traditional suspension bridge,it is found that the optimized structure can significantly improve the vertical stiffness of the main beam and reduce the internal force of the main beam and the middle tower.In summary,calculating and analyzing the single-span suspension bridge with double main cable with a main span of 1800m and the triple-tower twin-span suspension bridge with double main cable with a main span of 1800m+1800m by adopting the proposed double-cable suspension bridge,carrying out optimization of static performance of design parameters,gets a conclusion that multi-tower suspension bridge has excellent vertical stiffness by adopting double main cable.It has certain reference value for the design of long-span suspension bridges in the future.