Hysteretic behaviour of overlapped tubular k-joints under cyclic loading

Overlapped K-joints arise in truss type structures when one diagonal (overlap brace) intersects the other diagonal (through brace). In such joints, part of the through brace is hidden within the overlap brace, and the hidden toe of the through brace may or may not be welded to the chord. This study investigates the hysteretic behaviour of partially overlapped circular hollow section K-joints, with and without hidden welds, under cyclic loading. This study involved nine full-scale specimens, out of which four specimens had hidden welds. One joint was statically loaded and the remaining eight joints were cyclically loaded until failure. Chord plastification, brace local buckling, and cracking of the brace adjacent to welds were observed in these tests. The hysteretic performance indicators, such as ultimate capacity, joint ductility, energy dissipation, ultimate stiffness, etc., were established, which were then used to understand the hysteretic behaviour of overlapped K-joints. Results show that, compared with static loading, brace cracking occurred more easily under cyclic loading with a reduced joint capacity of up to 7% and a severely decreased ductility. Joints with hidden welds may exhibit a higher strength by approximately 10% and an increased hysteretic energy dissipation capacity, but with a reduction in joint ductility. The analysis of strain distributions around the joint zone indicates that, even though the joints with hidden welds experience lower strains, the hidden weld creates an asymmetric strain profile in the joints, which may be a weakness as some locations may become stress raisers leading to crack initiation.