Cantilever Box Girder Bridge Shear Lag Analysis

The box beam had great ability of resisting flexure and torsion. Moreover, it was light and had great span and was convenient to construct, so it could be widely used in all kinds of bridge structures especially in those huge and broad bridge. During the course of designing this kind of bridge, designers had to consider the influence of the shear lag. The meaning of 'shear lag' was that the bending normal stress near the boundary of wing plate and web plate is bigger than the stress near the midpoint of the wing plate. In the designing of pre-stressed concrete box beam and steel box beam, we must avoid the stress concentration. If the shear lag coefficientλis too large, the structure may split in some parts or lose stability and even broken, therefore, shear lag effect analysis is always a focus in bridge construction.This paper based on FoShanZiDong bridge—continuous rigid frame bridge, systematically analyzing the shear lag effect during its cantilever constructing. The results were significant and could be used as reference in engineering. According to the principle of three bar simulation method and the boundary condition of cantilever beam, the paper, aiming at the constructing of variable cross-section single-box two-compartment cantilever box beam, considered the influence of shear lag effect, deduced a group of differential equations about shear flow and analyzed the box beam's deformation behavior and normal stress distribution under deadweight.The deducing steps were showing as below:1.According to the principle of three bar simulation method, considering the top and bottom wing plate of single-box two-compartment beam as the structure including three reinforced poles and some tie-plates, and then deducing the differential equations, afterwards, introducing the boundary conditions into the equations and simplifying equations. Thereby, we could get the shear flow differential equations about single-box two-compartment cantilever box beam.2. During the construction of continuous rigid frame bridge, the structure was determinate before the change of structural system. In order to get more accurate simulating calculating results, the calculating model was simplified based on the special structure.3. In order to prove the correctness of differential equations deduced in the paper, the theoretical value and the simulating calculation results based on different conditions was compared and analyzed. Therefore, it could provide reference for the similar bridge's design and construction.