Fatigue and Ultimate Strengths of Plate Girders Fabricated by Robotics Welding

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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.