Fatigue strength of welded transverse stiffener joints under variable amplitude loading

Abstract

Long life fatigue tests are carried out using 2 m long plate girder specimens with transverse stiffeners, under constant amplitude loading and two types of typical variable amplitude loading. Fatigue cracks are initiated from the fillet weld toe at the top and bottom ends of the stiffeners; which are the compression and tension areas of the girder, respectively. Fatigue cracks in the tension area of the girders lead bottom flanges to failure, while those in the compression area are arrested in the vicinity of the weldment. Fatigue failure life of all specimens satisfies the Japanese standard category code D with a sufficient margin under constant and variable amplitude loading. Miner's law, either with or without cut-off limits, cannot evaluate the difference in fatigue life under two types of variable amplitude loading, but it can be estimated accurately by variable amplitude fatigue crack propagation analysis using fracture mechanics concepts.