偏心轴向荷载作用下薄壁箱梁的约束扭转翘曲应力研究

以薄壁箱梁的约束扭转分析理论为基础，将薄壁箱梁所受偏心轴向荷载作为一种外加双力矩荷载考虑，建立偏心轴向荷载作用下薄壁箱梁约束扭转的双力矩这一广义内力的计算公式。为了便于计算翘曲应力，进一步推导了扭转中心位置及主扇性坐标的实用计算公式。通过对一模型箱梁进行计算，并与按通用有限元软件ANSYS壳单元计算结果进行比较，验证了该文方法和所推导公式的正确性。详细分析箱室高宽比以及悬臂板宽度变化对偏心轴向荷载作用下薄壁箱梁约束扭转翘曲应力的影响。研究结果表明:箱室高宽比及悬臂板宽度对悬臂板端部翘曲应力的影响最大，对腹板与上翼缘、下翼缘交接处翘曲应力的影响相对较小；在偏心轴向分布荷载作用下，悬臂箱梁固定端横截面上控制点处的翘曲应力可达到初等梁应力的12%，不容忽视。

RESEARCH ON WARPING STRESS OF RESTRAINED TORSION FOR THIN-WALLED BOX GIRDER UNDER ECCENTRIC AXIAL LOAD

Based on the theory of restrained torsion for a thin-walled box girder, the equations of bimoment for the restrained torsion of a thin-walled box girder under an eccentric axial load are derived through taking the eccentric axial load as a kind of a bimoment load. The practical formulas for the twist centre and principal sectoral coordinate are further derived to simplify the calculation of warping stress. A box girder model is analyzed and the calculated stresses are in a good agreement with those obtained by the shell element of the finite element software ANSYS, validating the presented method and formulas. The influence of the variation of box depth-width ratios and cantilever plate widths on the warping stress for restrained torsion of a thin-walled box girder under an eccentric axial load is analyzed in detail. It is shown that: the depth-width ratio and the cantilever plate width affect remarkably the warping stress at the tip of a cantilever plate, while they have a smaller effect on the warping stress at the intersection of web and top or bottom plates; the warping stress at the control point on the fixed end cross section of the cantilever box girder under an eccentric axial load reaches 12% of that calculated by the elementary beam theory, which should not be ignored.