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Research on shear lag effect of box girder with variable width section

DOI：10.7511/jslx20210502001

 作者 单位 卢敏锋 兰州交通大学 土木工程学院, 兰州 730070 丁南宏 兰州交通大学 土木工程学院, 兰州 730070

将变宽度截面箱梁的剪力滞翘曲位移函数定义为三次抛物线形式,用能量变分原理建立了分析变宽截面箱梁剪力滞效应的控制微分方程,并用差分法求解此方程。分别计算了简支箱梁在集中荷载和均布荷载作用下的正应力,并用有限元法作了验证。将计算结果与等截面箱梁的应力进行对比,总结变宽箱梁剪力滞效应的分布规律。结果表明,均布荷载作用下,相对于等截面梁,变宽箱梁的顶板应力变化幅度更大,峰值更高,箱梁的顶板宽度变化对剪力滞效应影响较大;在集中荷载作用下,等截面与变宽度箱梁跨中截面的应力相近,应力分布曲线吻合较好,说明顶板宽度变化对剪力滞效应影响较小;分别在集中和均布荷载作用下,箱梁跨中截面应力均为正剪力滞分布状态。当箱梁顶板、底板和悬臂板宽度相等时,剪力滞效应控制微分方程也适用于等截面箱梁。

Shear lag warping displacement function of box girders with a variable width section would be defined as the form of cubic parabola.The governing equations for studying shear lag effect of box girders with a variable width section were established via the energy variation principle.The equations were solved by applying the finite difference method.The normal stress of the simply supported box girder subjected to concentrated and uniformly distributed loads respectively was calculated and validated by the finite element method.The calculated results were compared with the normal stress of the box girder with a uniform section.The regularity of distribution of shear lag effect of the box girder was achieved.It is shown that variation of top-flange width of the box girder has a great impact on shear lag effect and the rangeability and peak of normal stress in top flange of the box girder is bigger than that of a usual box girder,under uniformly distributed load.Values of normal stress in middle cross section of the box girder are basically close to a usual box girder and stress distribution curves are in good agreement,which indicates that variation of top-flange width of the box girder hardly affects the shear lag effect under concentrated load.Under a concentrated and uniformly distributed loads respectively,the stress in the middle cross section of the box girder is positive shear lag.When width of top slab,bottom slab and cantilever slabs of box girder are equal to each other,governing differential equations of shear lag effect is also applicable to a box girder with equal cross section.