Stress concentration factors (SCFs) and strain concentration factors (SNCFs) in multiplanar XX-joints made of circular hollow section, based on a numerical as well as experimental investigation, are considered in this paper. The numerical work investigates the influence of joint parameters β, γ and τ on the SCF and SNCF values. In the experiments, measurements have been carried out for determination of the SNCFs in a number of crown and saddle positions, for nine multiplanar XX-joints.

Introduction.

Offshore structures are usually constructed as lattice girders in which tubular members constitute the structural elements. Among the most fatigue sensitive areas in these structures are the weld toes at tubular multiplanar joint intersections. The evaluation of fatigue lives at these locations depend on the local hot spot stress range Sr (= σr * SCF), used in association with an S-N curve obtained numerically by FE analyses or experimentally by fatigue testing of such joints. Parametric equations for the determination of SCFs in various uniplanar joint geometries have been developed in the last decade. However for multiplanar joints due to complexity in geometry, there is an enormous lack of information. Because of this the multiplanar effects are generally ignored. This paper presents data on the SCFs and SNCFs based on primary stresses and strains at the crown and saddle positions measured along lines perpendicular to the weld toe determined by experiments and FE analyses. From the obtained data, by using a multivariable least squares curve fitting package, several formulae have been developed for determination of SCFs and SNCFs.

Numerical investigation.
General.

Sixty XX-joints have been analyzed. The emphasis was put on the effect of the joint parameters β, γ and τ on the SCFs and SNCFs. The considered values of the joint parameters and their combinations are illustrated in table 1.

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