Strength and collapse behaviors of stiffened patch-loaded web plates

本研究处理的是贴片加载腹板，它们是在用下水法竖立的梁上建模的。为了加固腹板，通常使用水平加强筋，因为承重加强筋不能安装在腹板上。然而，水平加强筋最初的目的不是为了抑制由局部载荷引起的屈曲，而是为了抑制由面内弯曲引起的屈曲。因此，有必要对加劲肋的有效性进行讨论。本研究采用弹塑性大挠度有限元程序进行分析，以水平加劲肋的存在、位置、刚度、面内弯矩大小等为参数。通过分析，得出以下结论：1。面内弯矩对贴片加载腹板的强度有较大的影响。在无面内弯矩或面内弯矩较小的情况下，加劲肋腹板的极限强度有时比不加劲肋腹板的极限强度要小。即使在上述情况下，水平加强筋也能增加腹板的屈曲强度。腹板的坍塌方式按参数分为以下四种类型；(1)由具有两条屈服线的机构坍塌。(2)腹板底部受屈服线和面内压缩屈服破坏。(3)腹板底部受面内压缩而坍塌。(4)由于主梁弯曲导致上下法兰屈服而倒塌。

This study deals with patch loaded web plates, modeling themselves upon girders erected with launching method. To stiffen such web plates, a horizontal stiffener is generally used because a load bearing stiffener cannot be arranged to such web plates. However, a horizontal stiffener is originaly aimed to restrain not the buckling due to the patch load but the buckling due to in-plane bending. Thus discussion on the effectiveness of a stiffener is required.In this study, an elasto-plastic large deflection FEM program is used for the analysis, and existence, location and stiffness of a horizontal stiffener, magnitude of in-plane bending moment and so on are adopted as parameters.Through the analysis, followings are found;1. Strength of patch loaded web plates are reduced considerably by in-plane bending moment.2. On a case of no or small in-plane moment, the ultimate strength of web plates with a horizontal stiffener is sometimes smaller than the strength of those with no stiffener.3. Even on above case, a horizontal stiffener increases buckling strength of web plates.4. The collapse mode of web plates are classified into following four types according to the parameters; (1) Collapse by the mechanism having two yield lines. (2) Collapse by yield lines and in-plane compression yielding at the bottom of the web plate. (3) Collapse by the in-plane compression at the bottom of the web plate. (4) Collapse by yielding of the upper and lower flanges due to the girder bending.