The Theoretical Investigations On The Local Distortion Effects Of Three-cell Box Girder Under Symmetrical Load

Thin-walled box section beams are widely used in passenger special line, so the local distortion effect in bridge design and stress analysis receives more attention than before.Based on the theoretical derivation and finite element numerical simulation, a lot of research about the local distortion effect of three-cell box girder under symmetrical loads are conducted. The main contents are as follows:(1) The stress condition under symmetrical load are studied for three-cell box girder web plate in the symmetric load mode and the edge web load model. By loading decomposition of single three-cell box girder under symmetrical load loading at the web, it can be found that the section of overall box girder can be seen as combined deformation of restrained torsion,combined distortion effect and shear lag effect. The formula of vertical distortion and equilibrium shear flow are derived with the cut-open single-chamber section. Then the stress of the combination of restrained torsion, shear lag effect and distortion effect under symmetrical load loading at the web is obtained using the elastic foundation analogy method.And The single box Three-edge web box girder under symmetrical loading mode can be decomposed into the web of symmetrical load loading mode.(2) For three-cell box simply supported beam and cantilever section in the web symmetrical load mode, numerical model are established using ANSYS with SHELL63.Numerical solution is extracted by superimposing the stress of numerical model and a lot of comparative analysis are conducted with the analytical solution. The results show that analytical solutions and numerical solutions are in good agreement in terms of value or variation, confirming the theoretical derivation is this paper is accuracy.(3) For three-cell box at the edge of the web box girder symmetrical loading mode, the analytical and numerical solutions of partial distortion stress in three-cell box girder section were compared using the decomposition method to make it equivalent to symmetrical loading mode in the web. The results showed that the analytical solutions and numerical solutions are consistent. At the same time it shows that the web side of the web and load mode symmetry symmetrical loading mode decomposition method utilizing load mutual equivalent method is feasible, and the theoretical derivation of this article is correct.(4) This paper introduces the concept of distortion in order to clearly reflect the distortion ratio of the bending stress accounted for shear lag effect. Through the analysis of cross-sectional distortion conclusions are as follows: The largest single box Three-section distortion occurs in parts of the cantilever roof, while the minimum distortion rate occurs at the junction of top and side of the web. Under the web symmetrical loading mode, the minimum distortion rate at L/2-section of simply supported beam is 15.21%, the maximumdistortion rate is 43.7%; the minimum distortion rate is 12.52% at the L/8-section of cantilever,the maximum distortion rate is 70.57%. Under side loading mode symmetrical webs, the minimum distortion rate at L/2-section of simply supported beam is 6.42%, the maximum distortion rate is 16.08%; the minimum distortion rate is 6.85% at the L/8-section of cantilever,the maximum distortion rate is 38.83%. The distortion of individual parts is relatively large In a single case in a three-compartment box girder being symmetrical load mode and should be received more attention. At the same time, the local distortion effects more obvious The load are closer the roof center under symmetrical load distribution in the cross section.