Elasto-Plastic Shear-Lag Analysis of Box Girders for Autostress Design

点击翻译按钮获取中文摘要

For autostress design of continuous steel box girder bridge,the shear-lag phenomena at cross sections on interior supports must be clarified. This study presents a practical and analytical procedure for obtaining elasto-plastic configurations of box girder having one axis of symmetry. The procedure is based on a thin-walled beam theory which can account the shear strain due to bending. The summary and results obtained for a two-span continuous box girder loaded symmetrically at two points are as follows;1. The normal stress in cross sections at interior support distribute parabolic in the flanges and cubic in the webs, due to shear-lag in the elastic load range. Then the plasticity occur at the four corners of the box cross section.2. Unknown parameters of the problem are the distances zeta and eta which represent the distances from a center of flange to the corner and from a center of web to that, respectively. The normal and additional bending moment due shear-lag are defined. In this time, the normal and shear strain distributions of elasticity are assumed.3. In the elastic portions of a cross section, the stress-strain relations are used and in the plastic, it is assumed that normal stress equals the yielding stress and shear stress does zero. The normal bending and additional bending moment distributions due shear-lag are approximated with those for elasticity theory.4. The unknown distances zeta and eta representing elasto-plastic boundaries of cross section can be obtained by solving above two equations on moments. As a result, elastic portions remain in the cross section, although webs are fully plastic, when the point loads become large and the load carrying capacity is still holded.