Fatigue and Ultimate Strengths of Plate Girders Fabricated by Robotics Welding

通过不同水平加劲肋端部间隙试件的疲劳试验，研究了水平加劲肋端部与横向加劲肋之间的间隙对板梁疲劳强度的影响。在水平加劲肋端部回弯侧焊趾处裂纹穿透腹板并出现在腹板对侧表面之前的寿命内，水平加劲肋端部间隙尺寸的影响很小。对于腹板中垂直扩展的贯通裂纹的扩展寿命而言，55 mm的水平加劲肋间隙在55 mm以下最有效。通过不同横向加劲肋间隙的横梁节点疲劳试验，研究了横向加劲肋末端与翼缘之间的间隙，即横向加劲肋末端间隙对横梁与主梁连接疲劳强度的影响。除翼缘焊接横向加劲肋外，横向加劲肋-腹板角焊缝在端部回火处出现疲劳裂纹，导致角焊缝断裂。腹板-翼缘角焊缝腹板一侧的焊趾处，除横向加劲肋焊接在翼缘外，另一处出现裂纹。横向加劲肋焊接在翼缘上的疲劳效果最好。在缝隙小于55 mm的情况下，水平加劲肋端间隙的增加对板的极限强度没有影响。为了研究水平加劲肋端间隙对板极限强度的影响，对带有水平加劲肋的方板进行了大挠度弹塑性分析。水平加劲肋间距在0 mm到55 mm之间时，极限强度几乎相同，但在55 mm到100 mm之间时，极限强度迅速下降。

The effects of the gap between the end of a horizontal stiffener and a transverse stiffener, so-called horizontal-stiffener-end gap, on the fatigue strength of plate girders was investigated by the gatigue tests of specimens with horizontal stiffeners of different horizontal-stiffener-end gaps. For the life until the crack initiated at the weld toe on the web side of the end return of a horizontal stiffener penetrated the web and appeared on the oppsite surface of the web, the effects of size in horizontal-stiffener-end gaps was small. For the propagation life of a through crack growing vertically in the web, the horizontal-stiffener -end gap of 55 mm was the most effective in the gap size less than 55 mm.The influence of the gap between the end of a transverse stifener and a flange, so-called transverse-stiffener-end gap, on the fatigue strength of the connection of a cross beam to a main girder was examined by the fatigue tests of cross-beam connections with transverse stiffeners of different transverse-stiffener-end gaps. Except for a transverse stiffener welded to a flange, a fatigue crack occurred at the end return of a trnasverse stiffener-web fillet weld, and broke the fillet weld. Except for the transverse stiffener welded to the flange, another crack was caused at the weld toe on the web side of the web-flange fillet weld. The transverse stifferner welded to the flange was the most effective for the fatigue. There was no effect of the increase of the horizontal-stiffener-end gap in the gap size less than 55 mm.The elastic-plastic large deflection analysis of a square plate with a horizontal stiffener under bending was carried out to inverstigate the influence of the horizontal-stiffener-end gap on the ultimate strength of plates. The ultimate strength was almost the same for the horizontal-stiffener-ens gaps between 0 mm and 55 mm, but it rapidly decreases for the gaps between 55 mm and 100 mm.