Hamid Ahmadi - Assistant Professor, Faculty of Civil Engineering, University of Tabriz
Mohammad Ali Lotfollahi-Yaghin - Professor, Faculty of Civil Engineering, University of Tabriz;
Shadi Asoodeh - MSc Student, Faculty of Civil Engineering, University of Tabriz

In the present paper, a set of parametric FE stress analyses is carried out for two-planar welded tubular DKT-jointsunder two different axial load cases. The analysis results are used to present general remarks on the effect ofgeometrical parameters on the stress concentration factors (SCFs) at the inner saddle, outer saddle, crown toe, andcrown heel positions on the main (outer) brace. Based on the results of finite element analyses which are verifiedagainst the experimental data, a complete set of SCF database is constructed. Then a new set of SCF parametricequations is developed through nonlinear regression analysis for the fatigue design of two-planar DKT-joints underaxial loads. An assessment study of these equations is conducted against the experimental data and the satisfaction ofthe criteria regarding the acceptance of parametric equations is checked. The hot-spot stress method for fatigue design of offshore structures relies on the accurate prediction of SCFs. Significant effort has been devoted by researchers to the study of SCFs in various uni-planar tubular connections. Nevertheless, for multi-planar joints covering the majority of practical applications, very few investigations have been reported due to the complexity and high cost involved. Despite the frequent use of two-planar DKT-joints in the offshore jacket structures, this is the first research proposing design formulae for the SCF calculation in such tubular joints

Offshore jacket structure, Multi-planar tubular joint, KT-joint, Fatigue, Stress concentration factor (SCF),Parametric equation