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Stress concentration factors at saddle and crown positions on the central brace of two-planar welded CHS DKT-connections

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Abstract

A set of parametric stress analyses was carried out for two-planar tubular DKT-joints under different axial loading conditions. The analysis results were used to present general remarks on the effects of the geometrical parameters on stress concentration factors (SCFs) at the inner saddle, outer saddle, and crown positions on the central brace. Based on results of finite element (FE) analysis and through nonlinear regression analysis, a new set of SCF parametric equations was established for fatigue design purposes. An assessment study of equations was conducted against the experimental data and original SCF database. The satisfaction of acceptance criteria proposed by the UK Department of Energy (UK DoE) was also checked. Results of parametric study showed that highly remarkable differences exist between the SCF values in a multi-planar DKT-joint and the corresponding SCFs in an equivalent uni-planar KT-joint having the same geometrical properties. It can be clearly concluded from this observation that using the equations proposed for uni-planar KT-connections to compute the SCFs in multi-planar DKT-joints will lead to either considerably under-predicting or over-predicting results. Hence, it is necessary to develop SCF formulae specially designed for multi-planar DKT-joints. Good results of equation assessment according to UK DoE acceptance criteria, high values of correlation coefficients, and the satisfactory agreement between the predictions of the proposed equations and the experimental data guarantee the accuracy of the equations. Therefore, the developed equations can be reliably used for fatigue design of offshore structures.

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Authors and Affiliations

  1. Faculty of Civil Engineering, University of Tabriz, Tabriz, 51664, Iran

    Hamid Ahmadi, Mohammad Ali Lotfollahi-Yaghin & Mohammad H. Aminfar

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  1. Hamid Ahmadi
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  2. Mohammad Ali Lotfollahi-Yaghin
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  3. Mohammad H. Aminfar
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Correspondence to Mohammad Ali Lotfollahi-Yaghin.

Additional information

Hamid Ahmadi was born in 1984. He got a BSc degree in civil engineering and an MSc degree in offshore structures engineering from the University of Tabriz, Iran. He is a PhD candidate in the Faculty of Civil Engineering at the University of Tabriz. He has authored over 30 technical papers and reports, as well as a book on dynamics of offshore structures. His current research includes the fatigue analysis and design of tubular joints, dynamics of offshore structures, and the structural reliability.

Mohammad Ali Lotfollahi-Yaghin was born in 1958. He got a BSc degree in civil engineering from the Isfahan University of Technology, Iran, an MSc degree in structural engineering from the University of Tabriz, Iran, and a PhD degree in offshore structures engineering from Heriot-Watt University, UK. He is working as an associate professor in the Faculty of Civil Engineering at the University of Tabriz. His current research interests include dynamics of offshore structures and reinforced concrete structures. He has authored over 100 technical papers and reports, as well as 2 books on FE analysis and dynamics of offshore structures.

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Ahmadi, H., Lotfollahi-Yaghin, M.A. & Aminfar, M.H. Stress concentration factors at saddle and crown positions on the central brace of two-planar welded CHS DKT-connections. J. Marine. Sci. Appl. 11, 83–97 (2012). https://doi.org/10.1007/s11804-012-1109-2

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  • DOI: https://doi.org/10.1007/s11804-012-1109-2

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