Strength of Square-Tube Connections under Combined Loads

An economical connection of intersecting square structural tubes can often be achieved by welding horizontal members, the beams, directly to a continuous vertical member, the column. The present investigation was limited to connections between square compact tubes of the same size. Combined loading tests were conducted on 11 fabricated specimens; five tests were with 4 in. sq (0.102 m) tubes and six with 6 in. sq (0.152 m) tubes. A theoretical analysis of strength was also made. The investigation showed that the strength of unreinforced connections in compact square tubes can be conservatively estimated by superposing interaction diagrams for: (1) General yielding in the arms due to combined bending and torsional moments and (2) localized column failure due to combined local buckling and crippling under axial load and bending. Equations for the construction of such diagrams are given.