Research About Approximate Calculation Method Of Optimal Cable Tension With Completion State For The Cable-stayed Bridge

Nowadays,the method of phased construction which is simple and feasible is carried out at long-span briges,including the cable-stayed bridges.However,there will be a variety of factors resulting finished dead state is different from the original design state under completion at the cable-stayed bridge that can not be controlled.In order to avoid this situation,we need to determine the middle state of the cable-stayed bridge which will be implemented and regulated strictly,at the same time,also need to adjust deviation of between internal force and displacement state in the process of the construction of cable-stayed bridge.Unstressed length which will be changed only under the condition of oneself tension altering or anchor moving and unstressed curvature ascertained when the components were installed are the two inherent properties of the cable-stayed bridge.It can be seen that as long as the structural system and the external load are fixed during the formation of the structure,the change of the cable tension is the only one of the change of the unstressed length.The second Fengdu Yangtze River Bridge in Chongqing is a long-span steel box girder cable-stayed bridge whose length is 1282 m and main span is 680 m,the system of main structure is the support system(i.e.semi floating system),bridge tower and pier attach each other,main beam is provided with a vertical support in the tower and the auxiliary pier and the edge(pier),and between the tower and main beam set a device restricting the horizontal and vertical displacement.Model for calculating is established according to the construction drawings and design requirements,and then for making sure consistency of internal force state and displacement state under the condition of finished dead state and target design state,we should ensure elastic curve continuous on the foundation of the theory of the unstressed state when the middle beam close down.This paper takes the second Fengdu Yangtze River Bridge as engineering example,which the finite element model simulated the construction process is established about by the Midas Civil.The vector of the elevation change of the control points of the concern sections come from the result which is caused by loading one of the unstressed length in each pair of stay cables,and these vectors are arranged in sequence to form the displacement influence matrix.With the adjustment of the height of the control point and the length of the unstressed cable length as the objective function,the descendingdirection of the function is obtained by the objective function and the descent speed will be controlled,at the same time,we calculate the weight coefficient in the objective function by the triangle rule,and use the powerful calculation function of Matlab to optimize the cable force by the iterative method,finally get the optimal state of the second Fengdu Yangtze River bridge.