Cyclic behavior of high-strength steel beam-to-column welded flange-bolted web connections

Abstract

Four Q690 high-strength steel beam-to-column moment connections, which use welded joints between beam and column flanges as well as a bolted beam web to the column flange, were tested under cyclic loading. The effects of beam-to-column welding details and panel zone strength were studied. Two pairs of welded flange details were incorporated, including the Chinese code-specified complete-joint-penetration (CJP) welded connections with backing plates where the bottom backing plate is reinforced by a fillet weld, and enhanced CJP welded connections with backing plates removed, weld roots backgouged, and further reinforced by fillet welds. Three panel zone thicknesses were designed to characterize strong, intermediate and weak panel zones, respectively. The test results show that backing plates should be removed in these moment connections to prevent brittle weld fracture, but still rendering only limited plastic hinge rotations in the order of 0.01–0.02 rad in the beam end before ductile fracture of the beam flange. The panel zone, however, survived even after a plastic shear rotation of 0.03 rad, demonstrating much higher plastic deformation capacity than the beam plastic hinge. This suggests that ductility can be exploited in 690 MPa high-strength steel panel zones, but not reliably in 690 MPa steel beams.