Research On The Unclosed Problem Of Forward And Backward Analysis Of Concrete Cable-stayed Bridges

The concrete cable-stayed bridge is widely used in long-span bridges due to its large span,beautiful appearance and practical advantages.As the concrete cable-stayed bridge is a complex high-order statically indeterminate structural system,its design and construction are more complex,especially the reasonable state of the bridge and the determination of reasonable construction force.First of all,based on the existing research results at home and abroad,this paper investigates and compares the methods of reasonable bridge establishment and reasonable construction status determination.Secondly,in order to solve the unclosed problem in the process of determining the construction state by using forward analysis and retrogression analysis method,the factors of the unclosed problem are analyzed,and the method of solving the unclosed problem caused by various factors based on the stress-free state method is also proposed.Based on this,using the finite element software Midas Civil to establish a three-dimensional model,the non-closed factor analysis of Jinnan Bridge,which is based on the project,was analyzed,and the influence degree of each factor was further analyzed.Finally,according to the introduction of the unstressed state method,the unclosed problem is solved,and the control parameters in each construction stage are obtained,which provides a theoretical basis for the construction control of cable-stayed bridges.The main conclusions are as follows:1.Taking the Jinnan Bridge as the background,this paper analyzes the various optimization methods for reasonable bridge status and compares the advantages and disadvantages of each method.2.Establish a set of retrogressive analysis model and forward analysis model.Analyze that the use of forward analysis and retrogression analysis method to determine the cable force during the construction phase,according to the results obtained by retrogressive analysis for forward analysis and calculation,the final results and design ideal state is not closed;Factors that affect the advance analysis and retrogressive analysis are unclosed,including structural system transformation factors,geometric nonlinear factors,shrinkage and creeping factors,and structural prestress factors;3.For the unclosed problems caused by the respective factors,carry out the cause analysis of the non-closed factors and propose measures to solve the unclosed problems caused by the respective factors: For the unclosed caused by the system conversion factors,the method of tuning can be adopted and the analysis can be carried out.When the counterforce and backlash analysis are applied prior to installation of the support,the temporary consolidation boundary is defined as the structural deformation and the state of the corresponding phases of the two methods is consistent before;the backward-forward analysis method that considers geometric nonlinearity is adopted and the convergence precision is improved,and the geometry can be improved.The non-closed influence caused by non-linearity is minimized;the shrinkage and creep factors and the unclosedness caused by the pre-stress factor can be used in the inverted-positive-fitting iterative method to close the cable-stayed force and the target cable force,and the bridge state is close to the target state.;4.On the basis of the actual project Jinnan Bridge,the degree of influence of the non-closed factor was analyzed.It is known that the non-closed influence caused by the shrinkage and creeping factor is the greatest,followed by the system transformation factor,and finally the geometric non-linear factor;5.Introduced the basic principle of no-stress method,discussed the influence of shrinkage and creep on the main beam linear shape;Finally,solved the unclosed problem caused by shrinkage-creep using the unstressed state-of-the-box iteration method,and extracted construction control parameters on this basis.Provides theoretical basis for the construction of cable-stayed bridges.