Experimental and Numerical Study of the Elastic SCF of Tubular Joints.

Mostafa Atteya,Gerhard Ersdal,John Wintle,Ove Mikkelsen

doi:10.3390/ma14154220

Abstract

This paper provides data on stress concentration factors (SCFs) from experimental measurements on cruciform tubular joints of a chord and brace intersection under axial loading. High-fidelity finite element models were generated and validated against these measurements. Further, the statistical variation and the uncertainty in both experiments and finite element analysis (FEA) are studied, including the effect of finite element modelling of the weld profile, mesh size, element type and the method for deriving the SCF. A method is proposed for modelling such uncertainties in order to determine a reasonable SCF. Traditionally, SCF are determined by parametric formulae found in codes and standards and the paper also provides these for comparison. Results from the FEA generally show that the SCF increases with a finer mesh, 2nd order brick elements, linear extrapolation and a larger weld profile. Comparison between experimental SCFs indicates that a very fine mesh and the use of 2nd order elements is required to provide SCF on the safe side. It is further found that the parametric SCF equations in codes are reasonably on the safe side and a detailed finite element analysis could be beneficial if small gains in fatigue life need to be justified.

Highlights

Fixed steel offshore structures are framed structures of tubular members welded together
The stress concentration factor (SCF) from the experimental work were updated by correction factors as per Table 2 to be compatible with the parametric code equations (Efthymiou formulae [13]) and the SCFs extracted from FE models
Stress concentration factors for cruciform tubular joints of a chord and brace intersection were determined at different positions along the weld toe of the chord using detailed finite element analysis and from strain gauge measurements made during experimental testing of four representative joints

Summary

Introduction

Fixed steel offshore structures (jackets) are framed structures of tubular members welded together. These are the most common type of offshore substructure for oil and gas exploration and to an increasing degree being used for offshore wind turbines. The structures are exposed to cyclic wave and wind loads in corrosive environments and fatigue is one of the main design criteria. The fatigue life assessment of welded joints is typically based on S–N curves in combination with a damage rule. The assumption of linear cumulative damage using the Palmgren–Miner rule is widely applied [1]

Methods

Results

Conclusion