Mechanical Performance Study On Long-span Road-Rail Partially Earth-Anchored Cable-Stayed Bridge

With the increasing of span,some restrictive factors in the structural system of conventional cable-stayed bridges,such as excessive stress of girder,are gradually highlighted,and the proposal of partially earth-anchored systems provides a new direction for the study of stress optimization of main girder on long-span cable-stayed bridges.In the thesis,the reasonable completion state,static response under external loads and seismic response of long-span partially earth-anchored cable-stayed bridges are studied preliminarily.The main work of the thesis is as follows:(1)The development history of cable-stayed bridges at home and abroad is discussed,and the research status of partially earth-anchored cable-stayed bridges at home and abroad is investigated.Then the relevant calculation theory of cable-stayed bridges,including static analysis theory,dynamic analysis theory,nonlinear theory and seismic analysis theory,is discussed,which lays a theoretical foundation for subsequent mechanical performance study.(2)Based on the finite element theory,the finite element model of partially earth-anchored cable-stayed bridges is established by using finite element software.The main work is to analyze reasonable completed state of partially earth-anchored cable-stayed bridges and study the mechanical behavior of structure under load.(3)The mechanical properties of partially earth-anchored cable-stayed bridges and conventional cable-stayed bridges are compared.The results show that partially earth-anchored of cable can reduce the maximum deflection of the main truss and the longitudinal displacement of the main tower.It also reduce the extreme value of stress in truss.In sum,partially earth-anchored cable-stayed bridges is better than conventional cable-stayed bridge in mechanical performance.With different construction schemes,the thesis compares the mechanical characteristics of partially earth-anchored cable-stayed bridges in the construction process,and studies the construction technology of partially earth-anchored cable-stayed bridges.(4)Based on the partial earth-anchored cable-stayed bridge,the thesis studies the influence of main design parameters on the static performance of the structure.Increasing the ratio of span,the length of anchor section and the ratio of tower height to span length,the result is enhancing the vertical stiffness of the structure and reduce the maximum deflection of mid-span.In addition,the increase of the length of earth-anchored section and the ratio of tower height to span length is beneficial to the stress state of truss.The changes in the height and width of the truss will affect the vertical stiffness of the structure,as will the stress on the truss and stay cables.(5)The thesis compares the seismic responses of partially earth-anchored cable-stayed bridges and conventional cable-stayed bridges,and the influence of partially earth-anchored of cable on the seismic performance of the structure is analyzed.Based on the response spectrum method,the number and dip angle of earth-anchored cable are changed to analysis its influence on the seismic performance of the structure.Based on the time history analysis method,the response of the structure under different seismic waves is calculated,and the difference between the seismic response of the structure under uniform excitation and traveling-wave excitation is compared to analysis the influence of traveling wave effect on the seismic response of the structure.In summary,the thesis analyses the static,dynamic and seismic performance of partially earth-anchored cable-stayed bridges through finite element simulation.The results show that partially earth-anchored system is slightly better than the conventional system in mechanical properties,which provides technical reference for the design and construction of such bridges in the future.