Numerical investigation and design rules for stress concentration factors of stainless-steel hybrid tubular joints

This paper describes a numerical study on stress concentration factors (SCFs) of stainless-steel hybrid tubular T-, Y- and X-joints with circular hollow sections (CHSs) and with square hollow sections (SHSs). The finite element models (FE models) were developed and validated against the corresponding test results available in the literature. The validated FE models were then utilized to perform an extensive parametric study containing 47 FE models for T-joints, 47 FE models for Y-joints and 47 FE models for X-joints. In total, 141 FE models were analyzed in the parametric study. The brace diameter to chord width ratio (β=d₁∕b₀), brace to chord thickness ratio (τ=t₁∕t₀) and chord width to thickness ratio (2γ=b₀∕t₀) were selected as the key geometric parameters in the parametric study. The SCFs at the hot spot locations obtained from the parametric study were compared against those calculated from the design formulae specified in the current design guidelines of the International Committee for the Development and Study of Tubular Structures (CIDECT). The comparison results show that the design formulae given in the CIDECT specification are not appropriate for predicting the SCFs of stainless-steel CHS-to-SHS hybrid tubular T-, Y- and X-joints. Therefore, new design equations were proposed in this study. It is shown that the values of SCFs calculated from the proposed design equations are generally in good agreement with the values obtained from the FEA.