Low cycle fatigue test was carried out on cruciform type specimens which were modeled on beam-to-column welded connection in steel structure. The column flange and the beam flange were used 22mm thick plate of SM490A steel. And the beam flange was welded to the column flange by CO_2 gas shield are welding with K-groove. The specimen types were as weld one, weld termination ground smooth one and base metal one. The fatigue tests were performed completely reversed strain-controlled with strain amplitude 0.2% to 2.7%. The test results showed that (1) crack initiation life and failure life of as weld specimens deteriorated to about 10%, and about 20% of those of base metal specimens, respectively, (2) crack initiation life and failure life of weld ground smooth specimens had tendencies to near the test values of as weld specimens at high-strain-amplitude, and to near the test values of base metal specimens at low-strain-amplitude,respectively,(3)low-cycle fatigue life process was dominated by fatigue crack growth life,(4) fracture patterns changed from fatigue fracture to ductile one on the border of 1.0% to 1.5% cyclic strain amplitude.
