| Long-span CFST arch bridge was characterized by large slenderness ratio,small width-span ratio and wide-height ratio,and obvious non-linear characteristics.During the construction process of arch truss by cantilever assembly with cable-stayed buckle method and pumping jacking method,arch truss structure was in an incomplete state,and the problem of non-linear stability was more prominent.In this paper,model experiment method,theoretical study method and numerical analysis method were combined to study the non-linear stability of CFST arch bridge during construction process,main study work,study results and conclusions were as follows:(1)Basic principles,equilibrium paths and analytical methods of branch point instability and extreme point instability were compared and studied,the characteristics of stability problems in CFST arch bridges were analyzed.Non-linear constitutive model of steel tube and core concrete in extreme point instability were compared and analyzed,and a program for constitutive generation of non-linear materials in stability study was programmed in C#language.Influence of initial imperfections on the non-linear stability of arch truss and tower were studied by numerical analysis method,the results show thatinitial imperfections have significant influence on the non-linear stability of arch truss and tower.Based on the statistical analysis of the limit values of construction offset for arch truss and tower,the recommended initial defect values of arch truss and tower were given.Aiming at the problem of large errors in the treatment of cable-tower connection in existing numerical analysis,suggestion for the treatment of connection between cable and tower was put forward,and the feasibility and accuracy of the method were verified by an example.(2)Based on the statistical analysis of members' mechanical properties and loading paths in CFST arch bridge,loading failure experiment of 9 CFST members with different slenderness ratio,eccentricity and concrete grade were carried out under axial and eccentric loads.Influence of stress,displacement,ultimate bearing capacity,failure modes and parameters variation on the mechanical properties of CFST compression-bending members were analyzed,mechanical properties and instability mechanism of CFST compression-bending members were revealed.The experimental results show that load-longitudinal strain curve and load-lateral deflection curve of CFST members were mainly composed of elasticity stage,elasticity-plasticity stage and descending stage.(3)Based on comparative analysis of different curvature solving methods,recommended solution method of curvature in parametric programming was given,accuracy of the proposed method was verified by an example,a calculation program of CFST section's curvature was compiled in C # language.Based on the stress characteristics of steel tube member,CFST member and the loading and failure experiments of CFST members,the critical curvature difference of steel tube members and CFST members were derived,discriminant criterion of member instability based on curvature difference and its corresponding calculation format were established.Based on the stress characteristics and failure modes of joints,the critical radian difference formulas of joints were deduced,and the criteria for judging the non-linear instability of joints based on radian difference and the corresponding calculation format were established.(4)Aiming at the non-linear stability of arch truss constructed by cantilever assembly with cable-stayed buckle method in construction process,influence of wind-resistant cable arrangement,arch truss offset and tower offset on the non-linear stability of arch truss in the construction process of cantilever assembly with cable-stayed buckle were studied respectively.The influence rules of wind-resistant cable and angle between wind-resistant cable and arch truss on the non-linear stability coefficient and instability mode of arch truss and tower were revealed,the relationship between wind-resistant cable's angle and non-linear stability coefficient of arch truss was established,the relationship between wind-resistant cable's angle and non-linear stability coefficient of tower was established,and the recommended angle between wind-resistant cable and arch truss was given.The causes of arch truss offset and tower offset were analyzed,and the influence rule of arch truss offset and tower offset on thenon-linear stability and non-linear instability mode of construction process were revealed.For there were many factors influencing the non-linear stability of construction process,and the interaction between influencing factors was complex,a non-linear stability optimal layout method for arch truss' s cable-stayed buckle cantilever assembly construction process based on tower-arch double control was proposed,the design variables and state variables in the non-linear stability optimal layout method were determined,and the objective function and its solution strategy of the non-linear stability optimal layout method were established.(5)Aiming at the non-linear stability of arch truss during pumping jacking construction process,the influence of arch truss' s concrete pouring sequence,variation of concrete stiffness and upward deflection of vault on the non-linear stability of arch truss during pumping jacking construction were studied respectively.The concrete pouring sequence of arch truss based on the optimal stability was proposed,the relationship between concrete stiffness' s variation and the non-linear stability coefficient of arch truss was established,the influence rule of concrete stiffness on the non-linear stability coefficient and non-linear instability mode of arch truss was revealed.The causes of upward deflection of vault were analyzed,the relationship between upward deflection of vault and rise-span ratio was revealed.The variation of displacement,axial force and bending moment of each section in arch truss during concrete pouring from arch foot to vault was studied,the variation law and instability mode of linearelasticity and non-linear stability of arch rib during pouring process were analyzed.For there were many factors influencing the non-linear stability of arch truss during pumping jacking construction process,and the interaction between these factors was complex,a non-linear stability optimal layout method for pumping jacking construction based on the control of arch truss offset was proposed,the design variables and state variables of the method were determined,objective function of the non-linear stability optimal placement method was established,and the solving strategy of the objective function was determined.(6)A CFST arch bridge(Pingnan third bridge in Guangxi province)with main span of 575 m was taken as an engineering example,spatial effect was considered,a 3D finite element model for construction stage was established,based on the study results of this paper,the non-linear stability of arch truss during cable-stayed buckle cantilever assembly construction process and pumping jacking construction process were discriminated and analyzed.The results show that during the construction of cantilever assembly with cable-stayed buckle,the components and joints of arch truss and tower were in a non-linear stable state,the non-linear stability coefficient of arch truss was obviously improved by wind-resistant cables in the transverse direction of bridge,the non-linear instability mode of arch truss was transverse instability,the non-linear stability coefficient of tower was 4.8,the non-linear instability mode of tower was longitudinal instability.During pumping and liftingconstruction of arch truss,members and joints in arch truss were in the state of non-linear stability.With the development of arch truss' s concrete pouring,the non-linear stability coefficient increases gradually when arch truss structure was filled with concrete in different steel tubes,the non-linear stability coefficients of two steel tubes on the symmetrical side of the cast-in-place arch truss were close and the difference increases gradually,the non-linear instability of arch truss during pouring process was manifested as transverse instability of arch truss. |
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