Tests to determine stress concentration factors for square bird-beak SHS joints under chord and brace axial forces

Bird-beak joints are a type of welded square hollow section (SHS) joint, the static strength of which is higher than that of conventional joints. Experimental analyses were conducted on the stress concentration factors (SCFs) of square bird-beak joints to obtain more information regarding their fatigue behavior. Twelve specimens, i.e., three conventional joints and nine square bird-beak joints, are separately tested by considering chord and brace axial force load cases. Both conventional and square bird-beak joints tested have a T-shape and are simply supported at their chord ends. Elastic strain distributions near the crown and saddle areas are measured, and strain concentration factors (SNCFs) at potential hot spots are calculated using an extrapolation approach. Quadratic extrapolation is suggested for the square bird-beak joints because linear extrapolation may underestimate SNCFs by up to 35%. Furthermore, critical locations are identified for square bird-beak joints subjected to chord and brace axial forces. A comparison indicates that the square bird-beak joints can produce lower stress concentration factors than the conventional or the diamond bird-beak joints with identical nondimensional parameters, especially when brace-to-chord width ratios are relatively small.