03.16: Multiplanar K‐joints on cold‐formed open sections: An experimental study with high strength steels

Abstract

ABSTRACTThe design, laboratory investigation and main results of an experimental programme on the joints of an innovative 3D truss made of high strength steel (HSS) is presented. An entire truss of triangular cross‐section was fabricated (two compression chords and a single tension chord) to provide realistic loading conditions. Both compression and tension chords were fabricated by cold forming hot‐rolled HSS plates by means of press braking. The chords were as follows: — an open angle‐type profile with 45° contained angle as tension chord (U‐chord), — a semi‐closed octagonal profile made of 3 sectors bolted along their length every 1.2 diameters as compression chords (P‐chord). The focus of this study is on the tension chords joints where a pair of tension and a pair of compression diagonals converge. Joints were tested to ultimate load by introducing shear to one bay of the truss at a time. Two design approaches for the joints were tested resulting in four individual tests.Ultimate load levels, stiffness and failure modes varied between the considered joint configurations. Stiffening increased the ultimate load by as much as 170% of that of the unstiffened version achieving higher utilisation of the tension chord, thus making more efficient use of HSS. The stiffness loss at loads close to failure varied between 60% – 80%. Two distinctive failure modes were observed, one caused by cracking of the welds connecting the diagonal's gusset plates to the tension chord while the second by cross‐section tensile fracture of the circular hollow section (CHS) diagonal.