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

用于自应力设计的箱梁弹塑性剪力滞分析

基本信息

批准号：
01550357
负责人：
USUKI Seizo
金额：
$ 1.15万
依托单位：
Akita University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1991
项目状态：
已结题

项目摘要

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.

在连续钢箱梁桥自应力设计中，必须明确内支座截面的剪力滞现象。本研究提出一个实用的分析程序，以获得具有一个对称轴的箱形梁的弹塑性配置。该程序是基于薄壁梁理论，可以考虑由于弯曲的剪切应变。本文对两点对称荷载作用下的两跨连续箱梁进行了研究。在弹性荷载范围内，由于剪力滞的影响，内支座截面上的正应力在翼缘呈抛物线分布，在腹板呈立方分布。然后在箱形截面的四个角处发生塑性变形.该问题的未知参数是距离zeta和eta，分别表示从翼缘中心到拐角的距离和从腹板中心到拐角的距离。定义了剪滞引起的正弯矩和附加弯矩。在此期间，假定了弹性的正应变和剪应变分布.在截面的弹性部分，使用应力-应变关系，在塑性部分，假设正应力等于屈服应力，剪应力为零。由剪滞效应引起的正弯矩和附加弯矩分布与弹性理论近似.通过求解上述两个矩量方程，可以得到代表截面弹塑性边界的未知距离zeta和eta。结果，当点荷载变大时，尽管腹板是完全塑性的，但弹性部分仍保留在横截面中，而承载能力仍保持不变。