Strength and collapse behaviors of stiffened patch-loaded web plates

本研究探讨局部受载腹板，模拟其架设于射水法架设之梁上。为了加固这样的腹板，通常使用水平加劲肋，因为承载加劲肋不能布置到这样的腹板。然而，水平加劲肋最初的目的不是为了抑制由于贴片载荷而引起的屈曲，而是为了抑制由于面内弯曲而引起的屈曲。本研究利用弹塑性大挠度有限元程序，以水平加劲肋的存在、位置、刚度、面内弯矩大小等为参数，进行分析，得到以下结论：1.面内弯矩的存在使局部荷载腹板的强度显著降低.在无弯矩或弯矩较小的情况下，设置水平加劲肋的腹板的极限强度有时小于未设置水平加劲肋的腹板的极限强度.即使在上述情况下，水平加劲肋也能提高腹板的屈曲强度。按参数将腹板的破坏模式分为以下四种：（1）双屈服线破坏模式。(2)腹板底部屈服线和面内压缩屈服破坏。(3)腹板底部面内受压破坏。(4)由于梁弯曲，上、下翼缘屈服而倒塌。

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.