Experimental and numerical stress analyses of tubular XT-joint

A typical large-scale, steel, multiplanar tubular XT-joint specimen was tested, with its in-plane and out-of-plane braces subjected to a total of 11 different load cases comprising the basic axial loading as well as axial loadings combined with in-plane-bending (IPB) and out-of-plane-bending (OPB) moments. The stress concentration factors (SCFs), strain concentration factors (SNCFs), and the SCF-to-SNCF ratio (S/N Ratio) at the potential hot spot stress locations were investigated. An average S/N Ratio of 1.16 was derived from all the test load cases. The SCFs at typical hot spot locations were also calculated using finite-element (FE) analysis. The good agreement between the numerical and the experimental SCF results confirmed the reliability of the numerical modeling of the XT-joint. In addition, the writers' SCF results were compared with Efthymiou's influence function (IF) method and the ones derived from the corresponding uniplanar T-/X-joints. A clearer understanding of the significance of the multiplanar effects for fatigue design was obtained through this comparison study.