Parametric stress analyses of steel multiplanar tubular XX-joints were carried out with 64 XX-joint models covering a wide range of geometrical parameters using the finite element method (FEM). A database of stress concentration factors (SCFs) at fixed hot spot stress locations was built up through about 320 runs of finite element (FE) analysis under five different load cases of brace and chord axial loads, in-plane-bending (IPB) and out-of-plane-bending (OPB) moments. A set of SCF design equations was established for general end loading. An assessment study of the equations was conducted by comparing the original FEM SCF database and two databases built upon experimental investigations to those calculated using the equations. The assessment results satisfied the latest parametric equation acceptance criteria set up by DEn. This confirmed the accuracy and reliability of the proposed SCF design equations. In addition, practical examples were given to illustrate the application of such equations.
Structural hollow sections of both circular (CHS) and rectangular (RHS), due to their excellent structural and mechanical properties, are widely used in various kinds of structures. Such structures can be found from offshore, such as the oil drilling platforms, to onshore, such as the roof top frame structures and the television transmission towers. Many tubular structures are subjected to cyclic loading. To offshore jacket structures, tubular joints are the crucial components used to integrate such circular members into a whole spatial functional structure. The structural discontinuity at the brace to chord intersection regions incurs large amount of stress concentration. Under cyclic service loading, fatigue failures always initiate at the areas where there are high-level stress concentrations. A recent study also reveals that fatigue cracking is the main cause of damage to North Sea steel structures.
