Derivation of the Probability Density Functions for the Local Joint Flexibility Factors in Axially Loaded Two-Planar Tubular DK-Joints of Offshore Structures

Authors

Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran

Abstract

Probability density functions of the involved random variables are essential for the reliability-based design of offshore structures. The objective of present research was the derivation of probability density function (PDF) for the local joint flexibility (LJF) factor, fLJF, in two-planar tubular DK-joints commonly found in jacket-type offshore structures. A total of 162 finite element (FE) analyses were carried out on 81 FE models of DK-joints subjected to two types of axial loading. Generated FE models were validated using available experimental data, FE results, and design formulas. Based on the results of parametric FE study, a sample database was prepared for the fLJF values and density histograms were generated for respective samples based on the Freedman-Diaconis rule. Nine theoretical PDFs were fitted to the developed histograms and the maximum likelihood (ML) method was applied to evaluate the parameters of fitted PDFs. In each case, the Kolmogorov-Smirnov and chi-squared tests were used to evaluate the goodness of fit. Finally, the Inverse Gaussian model was proposed as the governing probability distribution function for the fLJF. After substituting the values of estimated parameters, two fully defined PDFs were presented for the fLJF in tubular DK-joints subjected to two types of axial loading.

Keywords


Ahmadi H, Lotfollahi-Yaghin MA, “A probability distribution model for stress concentration factors in multi-planar tubular DKT-joints of steel offshore structures”, Applied Ocean Research, 2012, 34, 21-32.
Ahmadi H, Lotfollahi-Yaghin MA, “Geometrically parametric study of central brace SCFs in offshore three-planar tubular KT-joints”, Journal of Constructional Steel Research, 2012, 71, 149-161.
Ahmadi H, Lotfollahi-Yaghin MA, Aminfar MH, “Effect of stress concentration factors on the structural integrity assessment of multi-planar offshore tubular DKT-joints based on the fracture mechanics fatigue reliability approach”, Ocean Engineering, 2011, 38, 1883-1893.
Ahmadi H, Lotfollahi-Yaghin MA, Aminfar MH, “Geometrical effect on SCF distribution in uni-planar tubular DKT-joints under axial loads”, Journal of Constructional Steel Research, 2011, 67 (8), 1282-1291.
Ahmadi H, Lotfollahi-Yaghin MA, Shao YB, Aminfar MH, “Parametric study and formulation of outer-brace geometric stress concentration factors in internally ring-stiffened tubular KT-joints of offshore structures”, Applied Ocean Research, 2012, 38, 74-91.
Ahmadi H, Mayeli V, “Probabilistic analysis of the local joint flexibility in two-planar tubular DK-joints of offshore jacket structures under in-plane bending loads”, Applied Ocean Research, 2018, 81 (12), 126-140.
Ahmadi H, Mayeli V, “Development of a probability distribution model for the LJF factors in offshore two-planar tubular DK-joints subjected to OPB moment loading”, Marine Structures, 2019, 63 (1), 196-214.
Ahmadi H, Mayeli V, Zavvar E, “A Probability distribution model for the degree of bending in tubular KT-joints of offshore jacket-type platforms subjected to IPB moment loadings”, International Journal of Coastal and Offshore Engineering, 2019, 3 (2), 11-29.
Ahmadi H, Zavvar E, “The effect of multi-planarity on the SCFs in offshore tubular KT-joints subjected to in-plane and out-of-plane bending loads”, Thin-Walled Structures, 2016, 106, 148-165.
Ahmadi H, Ziaei Nejad A, “Local joint flexibility of two-planar tubular DK-joints in OWTs subjected to axial loading: Parametric study of geometrical effects and design formulation”, Ocean Engineering 2017, 136 (5), 1-10.
Ahmadi H, Ziaei Nejad A, “A study on the local joint flexibility (LJF) of two-planar tubular DK-joints in jacket structures under in-plane bending loads”, Applied Ocean Research, 2017, 64 (3), 1-14.
Ahmadi H, Ziaei Nejad A, “Geometrical effects on the local joint flexibility of two-planar tubular DK-joints in jacket substructure of offshore wind turbines under OPB loading”, Thin-Walled Structures, 2017, 114 (5), 122-133.
American Welding Society (AWS), “Structural welding code: AWS D 1.1.”, Miami (FL): American Welding Society, US, 2002.
Bouwkamp JG, Hollings JP, Masion BF, Row DG, “Effect of joint flexibility on the response of offshore structures”, Offshore Technology Conference (OTC), Houston, Texas, 1980, 455-464.
Buitrago J, Healy BE, Chang TY, “Local joint flexibility of tubular joints”, International Conference on Ocean, Offshore & Arctic Engineering (OMAE), Glasgow, UK, 1993, 405-417.
Chang E, Dover WD, “Parametric equations to predict stress distributions along the intersection of tubular X and DT-joints”, International Journal of Fatigue 1999, 21, 619-635.
Chang E, Dover WD, “Stress concentration factor parametric equations for tubular X and DT joints”, International Journal of Fatigue, 1996, 18 (6), 363-387.
Chen B, Hu Y, Tan M, “Local joint flexibility of tubular joints of offshore structures”, Marine Structures 1990, 3:177-197.
Chen B, Hu Y, Xu H, “Theoretical and experimental study on the local flexibility of tubular joints and its effect on the structural analysis of offshore platforms”, Proceedings of the 5th International Symposium on Tubular Structures, Nottingham, UK; 1993, 543-550.
Chen TY, Zhang HY, “Stress analysis of spatial frames with consideration of local flexibility of multiplanar tubular joint”, Engineering Structures 1996, 18 (6), 465-471.
Choo YS, Qian XD, Wardenier J, “Effects of boundary conditions and chord stresses on static strength of thick-walled CHS K-joints”, Journal of Constructional Steel Research, 2006, 62, 316-328.
Det Norske Veritas, “Rules for the design, construction and inspection of offshore structures”, Norway, 1977.
Efthymiou M, “Development of SCF formulae and generalized influence functions for use in fatigue analysis”, Offshore Tubular Joints (OTJ) 88, Surrey, UK, 1988.
Efthymiou M, “Local rotational stiffness of un-stiffened tubular joints”, RKER report; 1985, 185-199.
Fessler H, Mockford PB, Webster JJ, “Parametric equations for the flexibility matrices of single brace tubular joints in offshore structures”, Proceedings of the Institution of Civil Engineers 1986, 81, 659-673.
Fessler H, Mockford PB, Webster JJ, “Parametric equations for the flexibility matrices of multi-brace tubular joints in offshore structures”, Proceedings of the Institution of Civil Engineers, 1986, 81, 675-696.
Gao F, Hu B, “Local joint flexibility of completely overlapped tubular joints under out-of-plane bending”, Journal of Constructional Steel Research, 2015, 115, 121-130.
Gao F, Hu B, Zhu HP, “Local joint flexibility of completely overlapped tubular joints under in-plane bending”, Journal of Constructional Steel Research, 2014, 99, 1-9.
Gao F, Hu B, Zhu HP, “Parametric equations to predict LJF of completely overlapped tubular joints under lap brace axial loading”, Journal of Constructional Steel Research, 2013, 89, 284-292.
Golafshani AA, Kia M, Alanjari P, “Local joint flexibility element for offshore platforms structures”, Marine Structures, 2013, 33, 56-70.
Hoshyari I, Kohoutek R, “Rotational and axial flexibility of tubular T-joints”, Proceedings of the 3rd International Offshore and Polar Engineering Conference (ISOPE), Singapore, 1993, 192-198.
Hu Y, Chen B, Ma J, “An equivalent element representing local flexibility of tubular joints in structural analysis of offshore platforms”, Computers & Structures, 1993, 47 (6), 957-969.
Karamanos SA, Romeijn A, Wardenier J, “Stress concentrations in multi-planar welded CHS XX-connections”, Journal of Constructional Steel Research, 1999, 50, 259-282.
Kottegoda NT, Rosso R, “Applied statistics for civil and environmental engineers”, 2nd Edition, Blackwell Publishing Ltd, UK, 2008.
Lotfollahi-Yaghin MA, Ahmadi H, “Effect of geometrical parameters on SCF distribution along the weld toe of tubular KT-joints under balanced axial loads”, International Journal of Fatigue, 2010, 32, 703-719.
Morgan MR, Lee MMK, “Prediction of stress concentrations and degrees of bending in axially loaded tubular K-joints”, Journal of Constructional Steel Research, 1998, 45 (1), 67-97.
Nassiraei H, “Static strength of tubular T/Y-joints reinforced with collar plates at fire induced elevated temperature”, Marine Structures, 2019, 67, 102635.
Nassiraei H, Lotfollahi-Yaghin MA, Ahmadi H, “Static performance of doubler plate reinforced tubular T/Y-joints subjected to brace tension”, Thin-Walled Structures 2016, 108, 138-152.
Nassiraei H, Lotfollahi-Yaghin MA, Neshaei SA, Zhu L, “Structural behavior of tubular X-joints strengthened with collar plate under axially compressive load at elevated temperatures”, Marine Structures, 2018, 61, 46-61.
Nassiraei H, Mojtahedi A, Lotfollahi-Yaghin MA, Zhu L, “Capacity of tubular X-joints reinforced with collar plates under tensile brace loading at elevated temperatures”, Thin-Walled Structures, 2019, 142, 426-443.
Nassiraei H, Lotfollahi-Yaghin MA, Ahmadi H, Zhu L, “Static strength of doubler plate reinforced tubular T/Y-joints under in-plane bending load”, Journal of Constructional Steel Research, 2017, 136, 49-64.Smedley P, Fisher P, “Stress concentration factors for simple tubular joints”, Proceedings of the International Offshore and Polar Engineering Conference (ISOPE), Edinburgh, UK, 1991.
Ueda Y, Rashed SMH, Nakacho K, “An improved joint model and equations for flexibility of tubular joints”, Offshore Mechanics and Arctic Engineering, 1990, 112, 157-168.
Underwater Engineering Group, “Design of tubular joint for offshore structures”, UEG/CIRIA, London, UK, 1985.