Strain concentrations at intersection regions of a multiplanar tubular DX-joint

Abstract

A large-scale steel multiplanar tubular Double X-joint (DX-joint) specimen was tested such that its in-plane and out-of-plane braces were subjected to three different load cases of pure axial forces. The strain gradients at the joint intersection regions were measured and consequently the hot spot strain locations, and hence, the strain concentration factors (SNCFs) were determined. The shapes of the SNCF distributions and the peak SNCFs determined in the tests were found to be in good agreement with those obtained by finite element (FE) analyses, except for the load case where all the braces were subjected to axial tensile forces. In addition, the results at the peak hot-spot saddle locations were compared with those predicted using authors FE analyses, Efthymiou's influence function (IF) method (Efthymiou M. Development of SCF formulae and generalized influence functions for use in fatigue analysis. Proceedings of OTJ Conference, Surrey, UK, October 1988) and Romeijn's equations (Romeijn A, Puthli RS, De Koning CHM, Wardenier J. Stress and strain concentration factors of multiplanar joint made of circular hollow sections. Proceedings of the Second International Offshore and Polar Engineering Conference, San Francisco, USA, June 1992:384–93). Due to the multiplanar stiffening effect of the loaded out-of-plane braces, the IF method (Efthymiou M. Development of SCF formulae and generalized influence functions for use in fatigue analysis. Proceedings of OTJ Conference, Surrey, UK, October 1988) grossly overestimated the test results in the case where all the braces were subjected to axial tensile forces.