Stress concentrations in tubular DT-joints for fatigue design

Abstract

The present paper concerns the calculation of stress concentration factors (SCFs) in steel multi-planar welded tubular double T- (DT-) connections, due to axial loads. SCFs are used for the prediction of the hot-spot stress, in order to assess joint structural integrity against fatigue. in the course of the present study, extensive computational research is conducted, which correlates fairly well with available experimental data, and a large SCF database for multiplanar joints is developed. SCF values are computed in characteristic locations around the welds at the chord and brace sides. Using the SCF database, a simple and efficient methodology is proposed to calculate stress concentrations in DT-joints. The important phenomenon of carryover loading, which refers to the interaction between out-of-plane braces, is examined in detail. The proposed SCF design methodology is in the form of simple equations and diagrams of the joint parameters. The out-of-plane angle cp between the two braces is shown to be a crucial parameter for the SCF value. The SCF values predicted through the parametric equations are in good agreement with the finite-element results. Finally, a methodology for predicting the hot-spot stress and the fatigue life of tubular DT-joints is presented. The design approach presented in this paper is aimed toward a more reliable, yet simple, tubular DT-joint design for structures subjected to repeated loading.