Fatigue of Welded Steel Structures Due to Strong Earthquakes : II. Deteriorations of Welded Beam-to-Column Joints Due to Low-Cycle Fatigue

Abstract

This experiment was carried out from the viewpoint of evaluating the strength and the ductility of actual welded beam-to-column joints of steel structures in the event of earthquakes. The experiment consisted of three features to reveal the abovementioned objectives ; 1) a monotonic increasing load test to clarify the strength and toughness of steel plates stressed in the thickness direction, 2) a cyclic loading test to estimate the over-all load-deflection characteristics and the energy absorbing capacity of the welded joint, and 3) a low-cycle fatigue test to gain a quantitative criterion of ductility requirement for the structural safety against earthquakes. A special loading condition, that is, a bi-axial loading condition which contained the constant column axial force, was set up in order to examine whether or not a deterioration of the strength and the ductility would occur. Anisotropy of the steel plates and a relatively poor deformation capacity of the welded joints were clearly observed from the results of the monotonic increasing load test with regard to some particular welding procedures. A distinct fatigue strength deterioration of the welded joints is pointed out in comparison with that of the base metal, even though the energy absorbing capacity and the load-deflection relation do not differ from each other. The presence of the constant column axial force does not influence the energy absorbing capacity or the fatigue strength of the welded beam-to-column joints.