Study On Static Stability Of Multi-scale Model Of Over-kilometer-scale Suspension Bridge

Suspension bridge is a unique bridge type which has a long history.With the simple structure,clear transmission path and high material utilization rates,suspension bridge has made significant progress in ultra-thousand-meter bridges,and there is still great potential for the growth of its span.With the increase of the span of the suspension bridge,the height of the tower increases,the dead load increases,and the stability problems will also become more prominent.This thesis studies the static stability of over-kilometer-scale earth-anchored suspension bridges.A multi-scale finite element model was established,the first and second kind of stability analysis conducted,and the influencing factors of the static stability of the suspension bridge discussed.The research results could provide reference for future design calculation and simulation analysis of over-kilometer-scale earth-anchored suspension bridges.The main research work includes four parts:(1)Study of the static calculation theory and stability calculation method of suspension bridge.According to the mechanical characteristics of the suspension bridge,the static calculation theory and stability analysis theory of the suspension bridge were elaborated.Based on modern finite element softwares,the static calculation method and stability analysis method of the suspension bridge were summarized,with corresponding calculation flow charts drawn.(2)Study of the first kind of stability of the multi-scale model of suspension bridge.Taking the Nanjing Xianxin Road Yangtze River Bridge as the project background,a multi-scale model of the full bridge was established,whose tower was simulated with solid elements.The first kind of stability analysis was carried out at the bare tower construction stage and the service stage,considering dead load,live load and wind load.The results show that the buckling mode at the bare tower stage is longitudinal deflection of the main tower,and the most unfavorable load combination is the combination of constant load and longitudinal wind load;the buckling mode at the service stage is lateral deflection of the main tower,and the most unfavorable load combination is the combination of dead load,live load and lateral wind load.(3)Study of the second kind of stability of multi-scale model of suspension bridge.Based on the first type of stability analysis,with geometric nonlinearity and material nonlinearity considered,and initial defects imposed,the second type of stability analysis was conducted.The results show that the material yield leads to the structural instability,and the failure modes under different load combination have different characteristics.Compared with the first kind of instability,the stability safety coefficients of the second kind are greatly reduced.In the future,as the span of the suspension bridge increases,the nonlinear stability analysis will become necessary.(4)Study of influencing factors of static stability of suspension bridge.From the perspectives of structural simulation as well as design and construction,the effects of modeling objects,element selection,nonlinear factors,initial defects and stiffness of the main tower were analyzed.The stiffness of the main tower specifically considers the wall thickness,the steel bar area and the concrete grade.The results show that the stability results of the simplified main tower model or the use of beam elements to simulate the main tower can only represent or illustrate those of the full bridge to a certain extent;geometric nonlinearity and initial defects have little effect on the stability factor,while the material nonlinearity is the opposite and the stability safety coefficients are even more lower with the damage parameters considered;increasing section thickness contributes more to the improvement of the first kind of stability safety coefficients,and increasing reinforcement section area contributes more to the improvement of the second kind of stability safety coefficients,while increasing the concrete grade contributes little to both kinds of stability safety coefficients.The wall thickness of the tower,the area of the steel bar and the concrete grade are almost in proportion to the stability safety coefficients.