Research On Prestressed Concrete Cable-stayed Bridge Construction Control

Prestressed concrete (PC) cable-stayed bridges have extensive development in the whole world with their technical superiority such as long span ability and structural behavior, but cable-stayed bridges are high order statically indeterminate structures and suffer from lots of disadvantages in construction so that its stress system changes continuously with variation internal forces and geometrical state in construction, construction control must be taken in order to insure safety and satisfy design requirements under completion state and its requirements increase gradually with rapid development of cable-stayed bridges. The engineering background is super large Liuchong river cable-stayed bridge in Guizhou province. Forward iteration method was used to calculation and optimum proposal was taken to optimization analysis. Model calculation is based on actual problems in construction control and is used to analyze reasons and make proposals so as to guide construction correctly. Mainly research results are as follows:(1) BDCMS software was utilized to forward iteration calculation of construction control in Liuchong river cable-stayed bridge according to design requirements so that reasonable construction state and completion state are obtained. Section stress states of main girder are very reasonable in all stages which are standard section construction state, maximum double cantilever state, side-span closure state, mid-span closure state, second period pavement state, completion state and creep and shrinkage state10years after completion. Only No.27stay cable does two-time tension in the forward iteration calculation to get preferable stress conditions of the whole bridge so as to make convenience in construction and shorten construction period.(2) According to analyze stress conditions of main girder under load combination, forward iteration moments target was adjustment in unsatisfactory stress sections to achieve optimization purpose in completion state. Optimal methods consist of changing number of sub-working conditions (namely, increasing times of pouring concrete and times of cable-stayed tension) and decreasing ballast weights of closure sections and increasing cable forces in construction state.(3) Major design parameters are section weights, stay cable tension control and concrete shrinkage and creep coefficients in that these parameters have significant influence on structural linetype, stress and stay cable forces according to parameter sensitivity analysis on super large cable-stayed bridges. Stiffness variations of main girder and cable bent tower and stay cables are minor design parameter on account of its less impact on structural linetype, stress and stay cable forces.(4) Some methods and their notices in site such as cable forces tests, elevation tests, temperature tests and tower deflections are introduced. With respect to two forward fulcrum hanging basket problems in construction, MIDAS model was used to analyze and achieve relative comments which have good guiding significance in construction.