Research On Cable Force Optimization And Arch Ring Stress Regulation During Construction Of Long-span Concrete Arch Bridge With Cantilever Casting Mehtod

Concrete arch bridges constructed by cantilever casting started late in China,and there are still many problems in structural safety control that deserve further research and improvement.However,the concrete main arch belongs to cantilever curved beam structure before closure,so temporary structures such as buckle-cable,anchor cable and buckle-pylon are needed to ensure the safety of the arch structure during construction.Due to the large influence of the buckle-cable force on the internal force and alignment of the arch ring structure and there is usually no prestress in the concrete arch ring,if there is a slight deviation in the buckle-cable force during the construction process,the arch ring structure will easily crack,which will affect the structural safety of the cantilever casting construction system.In this paper,combining with the national natural science foundation project of"Theory and method of configuration and safety of concrete arch bridge with cantilever casting construction on multi-objective(No.51478049)",during the monitoring practice of two cantilever casting concrete arch bridges of 240m Shatuo Bridge and 180m Horseshoe River Bridge,corresponding research was carried out on cable force optimization and arch ring stress control during construction.The main work and results are as follows:(1)In order to consider the influence of geometric nonlinearity in cable during the cantilever casting construction of long-span concrete arch bridges,based on the high-precision two-node catenary cable element method,the secondary development of geometric nonlinearity cable element is carried out by using ANSYS platform,and its reliability is verified by classical examples.On this basis,based on the catenary cable element developed,the construction process of Shatuo Bridge is analyzed and researched,and the influence law of geometric nonlinearity in cable on the stress and alignment of arch ring and the force of buckle and anchor cable is revealed.(2)Because buckle-cable force based on backward demolition of ideal completed bridge state is difficult to meet the requirements of arch stress control during construction,therefore,in order to solve the problems,a step-by-step calculation method of the buckle-cable force is proposed based on the stress balance and the influence matrix method.Firstly,aiming at the stress safety control of arch ring during construction,iterative solution of initial tension force of buckle-cable is carried out,After that,the internal force state of the ideal completed arch ring is taken as the control target,and the cable force before closure is optimized and adjusted.the actual bridge verification of the above method was carried out during the construction of the Horseshoe River Bridge,and the optimal calculation effect of the buckle-cable force was great.(3)In order to reduce the times of cable tension and cable adjustment in the construction process and reduce the construction risks,the multi-objective optimization idea and solution method is introduced into the cable force optimization during the construction of cantilever casting concrete arch bridge and the cable force adjustment process required to meet the bridge completion state,and puts forward a solution method for reasonable construction cable force of cantilever casting concrete arch bridge based on multi-objective optimization.The initial tensile force of the buckle cable of Shatuo bridge during construction is optimized and solved.The results show that the fast non-dominated sorting genetic algorithm(NSGA-II)based on elitist strategy can achieve better results in cable force optimization of cantilever casting concrete arch bridge during construction,and provides a new idea for stress control of arch ring section of cantilever casting concrete arch bridge.(4)A real-time correction method of phased finite element model for long-span cantilever concrete arch bridge is proposed.Through reasonable selection of correction parameters,a parameterized phased finite element model is established to improve the calculation accuracy of the finite element model.Taking the phased construction system of Shatuo bridge as the research object,relevant tests are carried out to obtain the measured data of the geometric and physical characteristics of the relevant sections,and the finite element model is revised by using the measured data of the cable force,the cross-sectional strain of the arch ring,the alignment of the arch ring and the deviation of the buckle-pylon during the construction phase.The revised phased finite element model can provide technical support for the accurate regulation and control of the cross-sectional stress of the arch ring during the construction phase of the suspended concrete arch bridge.(5)In the construction of long-span cantilever casting concrete arch bridge,in order to better realize the goal of adjusting and controlling the tensile stress of arch ring section,an optimization method is proposed,which takes the buckle-pylon height and cable force as design variables.Taking Shatuo bridge as the research object,the section stress of arch ring is optimized during the cantilever casting construction.the calculation and analysis show that optimizing the buckle-pylon height and cable force at the same time can effectively reduce the tensile stress amplitude of arch ring section.On the other hand,based on the cable force optimization calculation results of different pylon span ratios,in a given variation interval of buckle-pylon height,the relationship curves between the amount of buckle-cable,the tensile stress of arch ring section,the deflection of arch ring and the stability target of cantilever casting system with the pylon span ratio are fitted,the optimization objective function of buckle-pylon height is established,and the corresponding reasonable design value of buckle-pylon height for construction is solved by linear programming method.(6)In order to reduce the risk that the tensile stress at the top and bottom edges of the arch ring section exceeds the limit during construction,a method for adjusting and controlling the stress of the arch ring section by arranging temporary prestress at the arch ring sections is proposed.The calculation formula of cross-section stress of arch ring under the coupling action of temporary prestress and cable force is deduced,and an iterative optimization solution program with arch ring stress as the objective function and cable force and prestress as design variables is compiled.Taking the Shatuo Bridge as the engineering background,a real bridge experimental research on the effect of temporary prestress on the stress control of arch ring section was carried out,and the influence law of the distribution length of temporary prestressed tendons in arch ring segments and the three distribution modes of arch ring section on the stress of arch ring section is discussed.