Behavior of branch-rotated T joints with cold-formed square hollow sections
An experimental investigation of branch-rotated T joints was carried out in which the branch was rotated by 45° with respect to its longitudinal axis. The main experimental parameters were the ratio of the width of the branch to the width of the chord, β′, with 0.38 ≤ β′ ≤ 1.00, and the ratio of the width of the chord to the thickness of the chord, 2γ, with 16.7 ≤ 2γ ≤ 33.3. Experimental results from 27 specimens showed that the ultimate strength increases and the failure mode changes under compression loading due to the rotated branch. The failure modes were out-of-plane bending yielding of the upper flange of the chord for β′ ≤ 0.85 and buckling of the chord web for 0.85 < β′ ≤ 1.00. Theoretical analysis was then carried out to compute the ultimate strength using a yield-line model for β′ ≤ 0.85 and web buckling model for β′ = 1.00. Linear interpolation was used for 0.85 < β′ < 1.00. Design formulas are presented for estimating the strength of T joints with a rotated branch.Key words: hollow structural section, truss T joint connections, yield-line instability, chord web instability, design equations.