Long-term fatigue behavior of the plate girder flange with a patch-plate-type attachment is investigated. Fatigue cracks are initiated from root gap and toe of transverse fillet weld between an attachment and a flange plate. Then, those two types of cracks join to propagate together, and finaly break down the flange plate. A finite element analysis shows the greater stress concentration at the root gap than that at the weld toe of the transverse fillet welds. Fatigue strength of the plate girder flange with a patch - plate - type attachment is demonstrated to be lower than the JSSC Category - F.
