Ultimate resistance of tubular double T-joints under axial brace loading

The results of a series of tests on multiplanar double T-joints with circular hallow sections under compressive brace loading are reported. The objective of the tests is to investigate influences of the brace to chord diameter ratio β, the transverse gap ratio ζ and the out-of-plane angle φ on the ultimate resistance of the joints. To interpret the results of the tests a simple plastic analysis of a closed ring model with collapse mechanisms corresponding to two observed failure types is attempted. In the range φ = 60° through 120° multiplanar TT-joints can be treated in design as two separate T-joints. An ultimate resistance equation is proposed on the basis of present and past tests results.