Structural behaviour and design of high strength steel CHS T-joints

This paper investigates the structural behaviour of high strength steel (HSS) circular hollow section (CHS) T-joints under brace axial compression. Finite element analysis on CHS T-joints using S460, S700, S900 and S1100 steel was conducted, and the chord plastification failure was examined. The effect of heat affected zones (HAZ) on the joint behaviour and influences of the steel grade, brace to chord diameter ratio (β) and chord diameter to wall thickness ratio (2γ) on the suitability of the CIDECT mean strength equations for HSS CHS T-joints were evaluated. The effect of HAZ on the initial stiffness of HSS CHS T-joints is found to be insignificant. The material softening in HAZ can lower the joint strength; however, the joint strength reduction is less pronounced. In general, the influence of β ratio on the suitability of the CIDECT mean strength equations for HSS CHS T-joints is minor. The CIDECT mean strength prediction is relatively accurate for S460 CHS T-joints and becomes increasingly unconservative for higher steel grade and larger 2γ ratio. This is because the improved yield stresses of HSS generally could not be fully utilised due to the adopted CIDECT indentation limit of 3% of chord diameter. It is suggested to tighten the range of 2γ ratio to be 2γ ≤ 40 for steel grades ranging from S460 to S700 and 2γ ≤ 30 for steel grades greater than S700 up to S1100 to allow for more effective use of HSS. The CIDECT validity range of 0.2 ≤ β ≤ 1.0 is also recommended for steel grades ranging from S460 to S1100. Mean and design strength equations modified from the CIDECT strength equations were proposed for HSS CHS T-joints with 2γ and β ratios which are within the suggested ranges.