开闭混合断面薄壁梁约束扭转分析

从薄壁微元体的纵向平衡出发，分析开闭混合断面薄壁梁约束扭转二次剪力流的传递和分布规律，提出了开闭混合断面薄壁梁约束扭转二次剪力流的分解计算方法，数值算例验证了该方法的合理性。引入反映二次剪应力对总剪应力影响程度的剪应力系数，结合悬臂梁数值算例，详细分析悬臂板宽度变化对剪应力系数和二次扭矩的影响规律。研究结果表明：开闭混合断面薄壁梁约束扭转时在腹板内产生很大的剪应力，当悬臂板宽度与闭合箱室宽度之比约为0.4时，腹板中点处剪应力系数可达到最大值2.8；悬臂板在约束扭转中承受很大的二次扭矩，甚至会等于闭合箱室承受的二次扭矩；对于箱室高宽比较大的薄壁梁，当悬臂板宽度与闭合箱室宽度之比约为0.7时，悬臂板承受二次扭矩的作用可得到充分发挥。

Analysis on restrained torsion of thin-walled beamswith open-closed mixed section

Through analyzing the longitudinal equilibrium of thin-walled differential bodies, this paper investigated the transmission and distribution law of secondary shear flow of thin-walled beam with open-closed mixed section under restrained torsion. A resolution computation method for the secondary shear flow was proposed and verified through numerical examples. Shear coefficient was introduced to reflect the influence of the secondary shear stress on the total shear stress. A numerical example of cantilever thin-walled beam was provided to analyze the influence of cantilever slab width on the shear stress coefficient and secondary torsion moment. It is shown that large shear stress occurs in the webs of thin-walled beam with open-closed mixed section under restrained torsion. The shear stress coefficient at the middle point of webs can reach the maximum value of 2.8 when the ratio of cantilever plate width to closed box cell width is approximately 0.4. The cantilever plates bear remarkable secondary torsion moment in the thin-walled beam under restrained torsion, even as large as that of the closed box cell. For a thin-walled beam with relative large height-width ratio of box cell, the ability of cantilever slabs in bearing the secondary torsion moment can be fully developed when the ratio of cantilever plate width to closed box cell width equals about 0.7.