Stress-Strain Relations and Plastic Fatigue Phenomenon of Welded Beam-To-Column Connections

Abstract

In order to examine the safety of steel structures against earthquakes, this paper deals with the stress-strain behavior and plastic fatigue strength of welded beam-to-column connections subjected to cyclic bending moments at relatively low cycles. A number of cantilever type specimens were subjected to cyclic loadings at the tips of the beams in a manner which induced constant tip deflection amplitudes, until the specimens were fractured at the beam ends. The loads, deflections and strains, at or near the beam ends, were measured during the cyclic loadings. From the test results, it was observed that local strains at or near the beam ends were distinctly influenced by the geometrical shapes of the beam ends, as well as by the thermal alteration due to welding. The values of the low cycle fatigue strengths of the actual beam ends were predicted by using linear relations in a log-log scale between the averaged non-dimensional strain ranges at the beam ends and the lives at the fracture or the crack initiation lives. Then they were compared with those of JIS SS 41 base metals and the welded joints. A remarkable deterioration of the fatigue strength was observed for the welded be am-to-column connections.