基于比拟杆法的多室箱梁竖弯段剪力滞效应计算及分析

为了分析梁轴线为竖向曲线的多室箱梁在桥墩处的剪力滞效应，基于比拟杆理论，通过用支座反力等效代替桥墩约束，求得了顶板沿桥轴线的轴力、剪力方程，算出了各加劲肋、腹板处加劲杆的换算面积，然后根据剪切变形协调方程，建立了考虑加劲肋影响的剪力滞微分方程组。将所建方程组的计算结果与采用ANSYS APDL软件建立的板壳有限元模型计算结果进行对比后发现：采用所建方程可避免求解2阶微分方程组的困难，易于使用，且能反映局部竖弯梁段的剪力滞效应变化情况，但计算精度随着叠加并积分的剪力流增加而降低；对于靠近计算起始端截面的加劲杆而言，比拟杆法计算应力与模型计算应力差值在10%左右；竖弯梁顶板最大应力处的剪力滞系数为1.4，大于直梁在该处的剪力滞系数1.2，直梁在该处的轴向应力与竖弯梁相比减小了5.9 MPa，可以认为存在竖弯的箱型梁对剪力滞的影响是不利的。

Calculation and Analysis on Shear Lag Effect of Multicell Box Girder at Vertical Bending Section Based on Analogy Rod Method

In order to analyze the shear lag effect of the multi-cell box girder at the pier with the beam axis as the vertical curve, based on the analogy rod theory, and by substituting the support reaction force equivalent for pier constraint, the axial force and shear force equation of the roof along the bridge axis is obtained to calculate the converted area of each ribbed stiffener and bracing piece at web is calculated. And then based on the compatibility equation of shear deformation, the differential equations set of shear force lag considering ribbed stiffener effect is established. By comparing with the calculation results of the plate and shell finite element model established by ANSYS APDL software, the calculation result of the established equations set shows that the established equation can avoid the difficulty to solve the second-order differential equations which is easy to use, and can reflect the changes in the shear lag effect of the local vertical bending beam. However, the calculation accuracy decreases with the increase of the superimposed and integrated shear flow. As for the bracing piece near the calculated starting end section, the difference value of the stress calculated by the analogy rod method and the stress calculated by the model is about 10.0%. The shear lag coefficient at the maximum stress of the roof of the vertical bending beam is 1.4, which is greater than the shear lag coefficient 1.2 at of the straight beam. The axial stress of the straight beam is reduced by 5.9 MPa compared with the vertical bending beam, which can be considered that the effect of the box beam with vertical bending on the shear lag is unfavorable.