Stress concentration factors of diamond bird-beak SHS T-joints under brace loading

T-joints made of hollow structural sections (e.g. circular hollow section (CHS) or square hollow section (SHS)) are often found in welded trusses that may be subjected to fatigue loading. The brace member of conventional T-joints (e.g. CHS-to-CHS, SHS-to-SHS and CHS-to-SHS T-joints) is perpendicular to the chord member. When the brace member and the chord member both rotates 45° a conventional SHS-to-SHS T-joint becomes a so-called “diamond bird-beak” SHS T-joint. Most of the research work on bird-beak joints has been focused on the static strength. Very limited information is available with regard to the fatigue strength of diamond bird beak joints. This paper will fill the knowledge gap in understanding the stress concentration factor (SCF) of this type of T-joints under brace loading (i.e. axial load in the brace and in-plane bending in the brace). A series of tests were conducted to measure the SCF of diamond bird-beak T-joints with a reasonable range of three key parameters, i.e. β (ratio of brace diameter to chord diameter), 2γ (ratio of chord diameter to chord thickness) and τ (ratio of brace thickness to chord thickness). It was found that the SCFs for the diamond bird beak T-joints are much lower than those for SHS-to-SHS and CHS-to-SHS T-joints, but just slightly smaller than those for CHS-to-CHS T-joints.