This paper presents the results of un-stiffened cantilever column subjected to incremental or constant amplitude cyclic loading. The objectives of this study are to investigate the extremely low cycle fatigue life of the column and verify the proposed strain based approach. During the test, fatigue cracks initiated from the weld toe at the corner and propagated along the weld toe. Finally, the column ruptured without a local buckling. The failure of low cycle fatigue induced by large cyclic deformation has been elucidated. In a further step, the crack initiation life was estimated based on the local strain by proposed simple approach. It is indicated that correlation between the test result and the estimated life was good enough.

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This study examined the fatigue strength of cruciform joints and longitudinal joints fabricated with laser-arc hybrid welding, in which tack welds were installed at the connection. The cruciform joints were tested under tensile cyclic loads and out-of-plane bending cyclic loads. In the longitudinal joints, four-point bending fatigue tests were performed on plate girders fabricated with the hybrid welding. In addition, finite element analysis was performed on the cruciform joint to investigate the effect of tack welds on stress concentration at weld toes. The test results revealed that the fatigue strengths of the hybrid welded joints are equivalent to those of arc welded joints with or without tack welds and satisfy the fatigue design curves specified in JSSC recommendation. Moreover, the analysis results indicated that tack welds have little influence on stress concentration at weld toes in cruciform joints fabricated with laser-arc hybrid welding.