Updating method on geometric shape control of continuous steel box girder bridges by incremental launching construction

Abstract

A new method of deviation vector transformation of geometric shape was proposed to improve the accuracy on geometric shape control of continuous steel box girder bridges by incremental launching construction.The method correct the transfer matrix method in the ideal state where the lateral and vertical deviations of longitudinal axis at the segments can be adjusted periodically.By firstly constructing a spatial coordinate system for identifying the geometric shape of the box bridge and taking the elevation and horizontal coordinates of the control points at both ends of the installed bridge segment as the basic variables, the actual and design coordinates of the control points will be obtained in the constructed coordinate system, constructing the vector of deviation system on geometric shape and the sum of vector squares, and then the extremum problem of the partial differential equation is solved to obtain the "transformed shape" with the lowest dispersion of overall deviation.The modified term appended to transfer matrix method aforementioned for bridge segment to be installed can be obtained ultimately by deriving from the "transformed shape" and "designed shape".Engineering practice shows that the horizontal and vertical maximal deflections on the axis of the whole bridge at post construction are less than 5 and 15 mm, respectively, by using the proposed method to control the geometric shape of a continuous steel box girder bridge by incremental launching construction method, meanwhile, the horizontal and vertical deflections on the axis of the segments above the permanent piers are less than 4 and 10 mm, respectively. The theoretical method has been verified with good effect in requirement of the code.