In this paper, the flexibility of tubular T-joints has been studied using a dynamic method of analysis. Kohoutek and Hoshyari (1991) considered a similar method, which employs the natural frequency, to study the inplane bending flexibility of tubular T-joints. The present paper uses a different theoretical model and carries out a parametric study using a total of 270 Finite Element analyses. The modes of deformation considered are inplane bending, out of plane bending and axial deformation of brace.
A more accurate fatigue life can be estimated for fixed offshore structures when hot spot stress is determined with a high accuracy at the tubular joints. A common method to analyse and design the tubular joints for fatigue life is the S-N method, where stress concentration factors arid nominal stress values are required as the crucial components: Stress concentration factor is usually determined by using parametric formulae and is not in the scope of this study. Nominal stress values in the members are calculated through a global analysis of the jacket structure, where a frame model with rigid joints is usually considered. The significance of including. the flexibility of tubular joints into analysis has been realised since the 1970s (DnV, 1977). Several research works have been carried out on the topic concluding that improvements can be made by accommodating the joint behaviour in the analysis (BouWkamp 1981, Tebbett 1982, Fessler et al. 1984, UEG 1984 and 1985, Efthymiou 1985, Ueda et aI1986). When spring stiffness of a joint is available method two of flexibility analysis, above, is easier to apply to a frame model. There are parametric equations for spring factors, proposed Elsewhere (Fessler 1984 and 1986, Efthymiou 1985, Ueda 1990), ba∼icallyas a solution to Equation (1) with cjl as unknown.
