Study About Shear Lag Effects Of Prestressed Concrete Box Girder Bridge During The Construction And Informing Phase

The pre-stressed concrete continuous or rigid frame box girder bridge in large-span is more likely to adopt self-balanced construction technology. And its stiffness and loading gradually formed with the cantilever construction process.Therefore, considering the cumulative effect of self balanced construction process in calculating the shear lag effect of girder is essential. At the same time, most researches ignored the influence of the position of lateral loading on shear lag effect of box girder.This paper aims to theoretical analyze and experimental study what are the accumulating effect of shear lag during the process of self-balance of PC box girder bridge and the effect of shear lag result from the different position in vehicle load of the bridge. From contrast analysis in theory, simulation and finite element, the main contents and corresponding results are as follows.1、Using the concept of generalized force and generalized displacement, setting the shear lag generalized longitudinal displacement among the roof of box girder and cantilever plate and bottom plate dividedly, adopting two times parabola as warping displacement function of flange plate, using the energy variation principle, this paper established the shear lag control differential equation of the box beam. The example shows the lateral load displacement has no influence on the shear lag effect of box girder, but has a great influence in longitudinal stress distribution on the bearing position.2、Based on the web shear deformation to correct shear lag warping displacement function of box beam, consociating the generalized displacement of the whole section and adopting the energy variation method, this paper established the bending shear lag differential equation of box girder. Using homogeneous general solution of differential equation to the shear lag displacement model of one-dimensional beam segment element, this paper established the element stiffness equation and calculated the element stiffness matrix and load matrix computation type. On the basis of calculation program worked out by FORTRAN language, this paper established a shear lag effect of finite segment model considering the web shear deformation. The example shows that single shear lag displacement algorithm taking web shear deformation into consideration is more accurate than three average shear lag displacement algorithm by traditional Timoshenko beams considering shear deformation, especially let the girder deformation be more close to the block element model.3、Through the model of finite segment and block element of Midas FEA and the analysis of test data from field collection, this paper summarized the rule of shear lag effect during the process of the construction of continuous beam as well as the influence of lateral displacement of vehicle load on the shear lag of box girder and verified the accuracy and operability of theoretical algorithm in the practical engineering application.