Study On Improvement Of Unstressed State Control Method For PC Bridge Constructed In Stages

The method of bridge constructed in stages has become the main way of forming large span bridge,and the unstressed state control method has been applied more and more widely because of its unique advantages in the process of determining the reasonable construction state of bridge constructed in stages.The equilibrium equation of unstressed state control method,which now is only established based on the plane beam element,needs to be further deduced on the space beam element with the development of the bridge structure towards the large span and the improvement of requirement for the structural analysis.What's more,PC bridge constructed in stages calculates the effect of shrinkage and creep of concrete on structure through iterations which could increase the workload and reduce the efficient.Therefore,it is urgent to propose the measures to reduce the number of iterations to advance the application of the method on PC bridge constructed in stages.The specific research contents are as follow:(1)According to the characteristics of bridge constructed in stages,the equilibrium equation of space beam element under the condition of geometric nonlinearity is established based on the principle of minimum potential energy,and the main factors that influence the internal force and displacement of the space beam structure are obtained.The correctness and reliability of equilibrium equation in this paper is proved with the space beam structure;The validity and correctness of the unstressed state control method of spatial beam element is confirmed though a PC pedestrian cable-stayed bridge with respect to the traditional plane beam element.(2)Based on the relationship between the stress state and the deformation of space beam element,the effection of concrete shrinkage and creep on the unstressed state amounts of space beam element is formulated in this paper;Then the method of accelerating iteration is presented and the calculation procedure of the original unstressed state method is improved.A concrete cable-stayed bridge is taken as an example to verify the calculation efficiency,accuracy and feasibility of the iteration formula of the stress free state method and the iterative calculation process.(3)This paper analyzes the Hunchun bridge respectively with the original unstressed state control method and the unstressed control acceleration iteration method,and draws the conclusion that the proposed unstressed state control accelerated iterative formula and the updated accelerated iterative calculation process reduce the number of iterations,improve the calculation efficiency and calculation accuracy in the rational construction state of cable-stayed bridges under the premise of the effection of concrete shrinkage and creep.(4)The technology of large scale cable adjustment of cable-stayed bridge is presented based on unstressed state control method.The correctness of basic principle of the technique is demonstrated through the cables tension of Hunchun Bridge,and points out the advantages compared with the traditional technology of large scale cable adjustment.