Degree of Bending in Axially Loaded Tubular KT-Joints of Offshore Structures: Parametric Study and Formulation
The fatigue life of tubular joints commonly found in
offshore industry is not only dependent on the value of hot-spot stress
(HSS), but is also significantly influenced by the through-thethickness
stress distribution characterized by the degree of bending
(DoB). The determination of DoB values in a tubular joint is essential
for improving the accuracy of fatigue life estimation using the stresslife
(S–N) method and particularly for predicting the fatigue crack
growth based on the fracture mechanics (FM) approach. In the
present paper, data extracted from finite element (FE) analyses of
tubular KT-joints, verified against experimental data and parametric
equations, was used to investigate the effects of geometrical
parameters on DoB values at the crown 0°, saddle, and crown 180°
positions along the weld toe of central brace in tubular KT-joints
subjected to axial loading. Parametric study was followed by a set of
nonlinear regression analyses to derive DoB parametric formulas for
the fatigue analysis of KT-joints under axial loads. The tubular KTjoint
is a quite common joint type found in steel offshore structures.
However, despite the crucial role of the DoB in evaluating the fatigue
performance of tubular joints, this paper is the first attempt to study
and formulate the DoB values in KT-joints.
[1] M. P. M. Connolly, A fracture mechanics approach to the fatigue
assessment of tubular welded Y and K-joints. PhD Thesis, University
College London, UK; 1986.
[2] E. Chang, W. D. Dover, “Prediction of degree of bending in tubular X
and DT joints,” International Journal of Fatigue, vol. 21, pp. 147–161,
1990.
[3] M. R. Morgan, M. M. K. Lee, “Prediction of stress concentrations and
degrees of bending in axially loaded tubular K-joints,” Journal of
Constructional Steel Research, vol. 45, pp. 67–97, 1998.
[4] UK Department of Energy (DoE), Background to new fatigue design
guidance for steel joints and connections in offshore structures, London,
UK; 1995.
[5] M. M. K. Lee, D. Bowness, “Estimation of stress intensity factor
solutions for weld toe cracks in offshore tubular joints,” International
Journal of Fatigue, vol. 24, pp. 861–875, 2002.
[6] W. Shen, Y. S. Choo, “Stress intensity factor for a tubular T-joint with
grouted chord,” Engineering Structures, vol. 35, pp. 37–47, 2012.
[7] A. C. Wordsworth, G. P. Smedley, “Stress concentrations at unstiffened
tubular joints,” Proceedings of the European Offshore Steels Research
Seminar, Paper 31, Cambridge, UK; 1978.
[8] M. Efthymiou, “Development of SCF formulae and generalized
influence functions for use in fatigue analysis,” OTJ 88, Surrey, UK;
1988.
[9] A. K. Hellier, M. Connolly, W. D. Dover, “Stress concentration factors
for tubular Y and T-joints,” International Journal of Fatigue, vol. 12,
pp. 13–23, 1990.
[10] M. R. Morgan, M. M. K. Lee, “Parametric equations for distributions of
stress concentration factors in tubular K-joints under out-of-plane
moment loading,” International Journal of Fatigue, vol. 20, pp. 449–
461, 1998. [11] E. Chang, W. D. Dover, “Parametric equations to predict stress
distributions along the intersection of tubular X and DT-joints,”
International Journal of Fatigue, vol. 21, pp. 619–635, 1999.
[12] Y. B. Shao, “Geometrical effect on the stress distribution along weld toe
for tubular T- and K-joints under axial loading,” Journal of
Constructional Steel Research, vol. 63, pp. 1351–1360, 2007.
[13] Y. B. Shao, Z. F. Du, S. T. Lie, “Prediction of hot spot stress distribution
for tubular K-joints under basic loadings,” Journal of Constructional
Steel Research, vol. 65, pp. 2011–2026, 2009.
[14] M. A. Lotfollahi-Yaghin, H. Ahmadi, “Effect of geometrical parameters
on SCF distribution along the weld toe of tubular KT-joints under
balanced axial loads,” International Journal of Fatigue, vol. 32, pp.
703–719, 2010.
[15] H. Ahmadi, M. A. Lotfollahi-Yaghin, M. H. Aminfar, “Geometrical
effect on SCF distribution in uni-planar tubular DKT-joints under axial
loads,” Journal of Constructional Steel Research, vol. 67, pp. 1282–
1291 2011.
[16] M. A. Lotfollahi-Yaghin, H. Ahmadi, “Geometric stress distribution
along the weld toe of the outer brace in two-planar tubular DKT-joints:
parametric study and deriving the SCF design equations,” Marine
Structures, vol. 24, pp. 239–260, 2011.
[17] H. Ahmadi, M. A. Lotfollahi-Yaghin, “Geometrically parametric study
of central brace SCFs in offshore three-planar tubular KT-joints,”
Journal of Constructional Steel Research, vol. 71, pp. 149–161, 2012.
[18] H. Ahmadi, M. A. Lotfollahi-Yaghin, Y. B. Shao, “Chord-side SCF
distribution of central brace in internally ring-stiffened tubular KTjoints:
A geometrically parametric study,” Thin-Walled Structures, vol.
70, pp. 93−105, 2013.
[19] D. Bowness, M. M. K. Lee, “Fatigue crack curvature under the weld toe
in an offshore tubular joint,” International Journal of Fatigue, vol. 20,
pp. 481–490, 1998.
[20] C. K. Lee, S. T. Lie, S. P. Chiew, Y. B. Shao, “Numerical models
verification of cracked tubular T, Y and K-joints under combined loads,”
Engineering Fracture Mechanics, vol. 72, pp. 983–1009, 2005.
[21] Y. B. Shao, S. T. Lie, “Parametric equation of stress intensity factor for
tubular K-joint under balanced axial loads,” International Journal of
Fatigue, vol. 27, pp. 666–679, 2005.
[22] Y. B. Shao, “Analysis of stress intensity factor (SIF) for cracked tubular
K-joints subjected to balanced axial load,” Engineering Failure
Analysis, vol. 13, pp. 44–64, 2006.
[23] American Welding Society (AWS), Structural welding code: AWS D
1.1. Miami (FL), US; 2002.
[24] S. T. Lie, C. K. Lee, S. M. Wong, “Modeling and mesh generation of
weld profile in tubular Y-joint,” Journal of Constructional Steel
Research, vol. 57, pp. 547–567, 2001.
[25] H. Ahmadi, M. A. Lotfollahi-Yaghin, Y. B. Shao, M. H. Aminfar,
“Parametric study and formulation of outer-brace geometric stress
concentration factors in internally ring-stiffened tubular KT-joints of
offshore structures,” Applied Ocean Research, vol. 38, pp. 74–91, 2012. [26] P. Smedley, P. Fisher, “Stress concentration factors for simple tubular
joints,” Proceedings of the International Offshore and Polar
Engineering Conference (ISOPE), Edinburgh; 1991. pp. 475–83.
[27] IIW-XV-E, Recommended fatigue design procedure for welded hollow
section joints, IIW Docs, XV-1035-99/XIII-1804-99, International
Institute of Welding, France; 1999.
[28] UK Health and Safety Executive, OTH 354: Stress concentration factors
for simple tubular joints- assessment of existing and development of new
parametric formulae, Prepared by Lloyd’s Register of Shipping, UK,
1997.
[1] M. P. M. Connolly, A fracture mechanics approach to the fatigue
assessment of tubular welded Y and K-joints. PhD Thesis, University
College London, UK; 1986.
[2] E. Chang, W. D. Dover, “Prediction of degree of bending in tubular X
and DT joints,” International Journal of Fatigue, vol. 21, pp. 147–161,
1990.
[3] M. R. Morgan, M. M. K. Lee, “Prediction of stress concentrations and
degrees of bending in axially loaded tubular K-joints,” Journal of
Constructional Steel Research, vol. 45, pp. 67–97, 1998.
[4] UK Department of Energy (DoE), Background to new fatigue design
guidance for steel joints and connections in offshore structures, London,
UK; 1995.
[5] M. M. K. Lee, D. Bowness, “Estimation of stress intensity factor
solutions for weld toe cracks in offshore tubular joints,” International
Journal of Fatigue, vol. 24, pp. 861–875, 2002.
[6] W. Shen, Y. S. Choo, “Stress intensity factor for a tubular T-joint with
grouted chord,” Engineering Structures, vol. 35, pp. 37–47, 2012.
[7] A. C. Wordsworth, G. P. Smedley, “Stress concentrations at unstiffened
tubular joints,” Proceedings of the European Offshore Steels Research
Seminar, Paper 31, Cambridge, UK; 1978.
[8] M. Efthymiou, “Development of SCF formulae and generalized
influence functions for use in fatigue analysis,” OTJ 88, Surrey, UK;
1988.
[9] A. K. Hellier, M. Connolly, W. D. Dover, “Stress concentration factors
for tubular Y and T-joints,” International Journal of Fatigue, vol. 12,
pp. 13–23, 1990.
[10] M. R. Morgan, M. M. K. Lee, “Parametric equations for distributions of
stress concentration factors in tubular K-joints under out-of-plane
moment loading,” International Journal of Fatigue, vol. 20, pp. 449–
461, 1998. [11] E. Chang, W. D. Dover, “Parametric equations to predict stress
distributions along the intersection of tubular X and DT-joints,”
International Journal of Fatigue, vol. 21, pp. 619–635, 1999.
[12] Y. B. Shao, “Geometrical effect on the stress distribution along weld toe
for tubular T- and K-joints under axial loading,” Journal of
Constructional Steel Research, vol. 63, pp. 1351–1360, 2007.
[13] Y. B. Shao, Z. F. Du, S. T. Lie, “Prediction of hot spot stress distribution
for tubular K-joints under basic loadings,” Journal of Constructional
Steel Research, vol. 65, pp. 2011–2026, 2009.
[14] M. A. Lotfollahi-Yaghin, H. Ahmadi, “Effect of geometrical parameters
on SCF distribution along the weld toe of tubular KT-joints under
balanced axial loads,” International Journal of Fatigue, vol. 32, pp.
703–719, 2010.
[15] H. Ahmadi, M. A. Lotfollahi-Yaghin, M. H. Aminfar, “Geometrical
effect on SCF distribution in uni-planar tubular DKT-joints under axial
loads,” Journal of Constructional Steel Research, vol. 67, pp. 1282–
1291 2011.
[16] M. A. Lotfollahi-Yaghin, H. Ahmadi, “Geometric stress distribution
along the weld toe of the outer brace in two-planar tubular DKT-joints:
parametric study and deriving the SCF design equations,” Marine
Structures, vol. 24, pp. 239–260, 2011.
[17] H. Ahmadi, M. A. Lotfollahi-Yaghin, “Geometrically parametric study
of central brace SCFs in offshore three-planar tubular KT-joints,”
Journal of Constructional Steel Research, vol. 71, pp. 149–161, 2012.
[18] H. Ahmadi, M. A. Lotfollahi-Yaghin, Y. B. Shao, “Chord-side SCF
distribution of central brace in internally ring-stiffened tubular KTjoints:
A geometrically parametric study,” Thin-Walled Structures, vol.
70, pp. 93−105, 2013.
[19] D. Bowness, M. M. K. Lee, “Fatigue crack curvature under the weld toe
in an offshore tubular joint,” International Journal of Fatigue, vol. 20,
pp. 481–490, 1998.
[20] C. K. Lee, S. T. Lie, S. P. Chiew, Y. B. Shao, “Numerical models
verification of cracked tubular T, Y and K-joints under combined loads,”
Engineering Fracture Mechanics, vol. 72, pp. 983–1009, 2005.
[21] Y. B. Shao, S. T. Lie, “Parametric equation of stress intensity factor for
tubular K-joint under balanced axial loads,” International Journal of
Fatigue, vol. 27, pp. 666–679, 2005.
[22] Y. B. Shao, “Analysis of stress intensity factor (SIF) for cracked tubular
K-joints subjected to balanced axial load,” Engineering Failure
Analysis, vol. 13, pp. 44–64, 2006.
[23] American Welding Society (AWS), Structural welding code: AWS D
1.1. Miami (FL), US; 2002.
[24] S. T. Lie, C. K. Lee, S. M. Wong, “Modeling and mesh generation of
weld profile in tubular Y-joint,” Journal of Constructional Steel
Research, vol. 57, pp. 547–567, 2001.
[25] H. Ahmadi, M. A. Lotfollahi-Yaghin, Y. B. Shao, M. H. Aminfar,
“Parametric study and formulation of outer-brace geometric stress
concentration factors in internally ring-stiffened tubular KT-joints of
offshore structures,” Applied Ocean Research, vol. 38, pp. 74–91, 2012. [26] P. Smedley, P. Fisher, “Stress concentration factors for simple tubular
joints,” Proceedings of the International Offshore and Polar
Engineering Conference (ISOPE), Edinburgh; 1991. pp. 475–83.
[27] IIW-XV-E, Recommended fatigue design procedure for welded hollow
section joints, IIW Docs, XV-1035-99/XIII-1804-99, International
Institute of Welding, France; 1999.
[28] UK Health and Safety Executive, OTH 354: Stress concentration factors
for simple tubular joints- assessment of existing and development of new
parametric formulae, Prepared by Lloyd’s Register of Shipping, UK,
1997.
@article{"International Journal of Architectural, Civil and Construction Sciences:70130", author = "Hamid Ahmadi and Shadi Asoodeh", title = "Degree of Bending in Axially Loaded Tubular KT-Joints of Offshore Structures: Parametric Study and Formulation", abstract = "The fatigue life of tubular joints commonly found in
offshore industry is not only dependent on the value of hot-spot stress
(HSS), but is also significantly influenced by the through-thethickness
stress distribution characterized by the degree of bending
(DoB). The determination of DoB values in a tubular joint is essential
for improving the accuracy of fatigue life estimation using the stresslife
(S–N) method and particularly for predicting the fatigue crack
growth based on the fracture mechanics (FM) approach. In the
present paper, data extracted from finite element (FE) analyses of
tubular KT-joints, verified against experimental data and parametric
equations, was used to investigate the effects of geometrical
parameters on DoB values at the crown 0°, saddle, and crown 180°
positions along the weld toe of central brace in tubular KT-joints
subjected to axial loading. Parametric study was followed by a set of
nonlinear regression analyses to derive DoB parametric formulas for
the fatigue analysis of KT-joints under axial loads. The tubular KTjoint
is a quite common joint type found in steel offshore structures.
However, despite the crucial role of the DoB in evaluating the fatigue
performance of tubular joints, this paper is the first attempt to study
and formulate the DoB values in KT-joints.", keywords = "Tubular KT-joint, fatigue, degree of bending (DoB),
axial loading, parametric formula.", volume = "9", number = "6", pages = "707-10", }
