Parametric equations for distributions of stress concentration factors in tubular K-joints under out-of-plane moment loading

An extensive parametric study, using finite elements, of the stress concentration factors in tubular K-joints commonly found in offshore platforms is presented. This study covers a comprehensive range of geometric joint parameters for unbalanced out-of-plane moment loading. The results of the study were first used to assess the widely used parametric equations of Efthymiou (Proceedings of the Conference on Recent Developments in Tubular Joints Technology, Surrey, 1988, p. 2–1) and Lloyds Register (Proceedings of the 1st International Society of Offshore Polar Engineers Conference, 1991, Edinburgh), which provide predictions of stress concentration factors at the saddle on the outer surfaces of the chord and the brace as a function of the joint geometric ratios. The database of thin shell finite element results generated was then used to develop parametric equations for predicting stress concentration factors at key locations around the joint intersection on the outer, as well as the inner, surfaces of the chord. The reliability of the proposed and existing parametric equations was then assessed using the acrylic joint database published by the UK Department of Energy (Draft Background to New Fatigue Design Guidance for Steel Joints and Connections in Offshore Structures, 1995). The paper concludes with fracture mechanics fatigue calculations to demonstrate that the information provided from the proposed equations could be utilised to obtain accurate, and safe, fatigue life estimates