Stress Concentration Factors in FRP Strengthened Tubular T-joints Under Brace In-Plane Bending and Out-of-Plane Bending Moments


1 PhD Candidate, University of Tehran

2 Assocciate Professor, University of Tehran

3 Assisstant Professor, University of Tehran


This research is dedicated to study the relative stress concentration factors (SCF) at FRP strengthened tubular T-joint subjected to brace in-plane and out-of-plane bending moments using Finite Element Analyses performed by ABAQUS software package. Validation analysis for the finite element model of the unstiffened joint is performed against the experimental results together with the Lloyd’s Register and API equations. The effectiveness of using three different types of FRP materials such as Glass/Vinyl ester, Glass/Epoxy (Scotch ply 1002) and Carbon/Epoxy (T300-5208) on enhancing the fatigue life of tubular T-joints through computing the SCFs was investigated in three schemes. At first the chord alone was strengthened in order to investigate the effects of strengthening the chord member on SCFs. In the second phase, FRP was applied only on the brace member to study the brace strengthening effects, and in the third phase, both of the chord and brace members were strengthened. Promising results derived from analysis which show that FRP strengthening method can effectively decrease the SCF values at T-joints.


[1] Jia, J., An efficient nonlinear dynamic approach for calculating wave induced fatigue damage of offshore structures and its industrial applications for lifetime extension, ‘‘Applied Ocean Research’’, Vol. 30, 189-198, 2008. [2] API (American Petroleum Institute), Recommended practice for planning, designing and constructing fixed offshore platforms - working stress design, API RP 2A WSD, 22nd edition, 2014. [3] Lesani, M., Bahaari, M.R., Shokrieh, M.M., Numerical investigation of FRP-strengthened tubular T-joints under axial compressive loads, ‘‘Composite Structures’’, Vol. 100, 71-78, 2013. [4] Hollaway, L.C., Cadei, J., 2002, Progress in the technique of upgrading metallic structures with advanced polymer composites, ‘‘Progress in Structural Engineering and Materials’’, Vol. 4(2), 131-148. [5] Zhao, X.L., Zhang, L., State of the art review on FRP strengthened steel structures, ‘‘Engineering Structures’’, Vol. 29(8), 1808-1823, 2007. [6] Zhao, X.L., FRP strengthened metallic structures, ‘‘Thin Walled Structures’’, Special Issue, Vol. 47(10), 1019, 2009. [7] Jiao, H., Zhao, X.L., CFRP strengthened butt-welded very high strength (VHS) circular steel tubes, ‘‘Thin-Walled Structures’’, Vol. 42(7), 963-978, 2004. [8] Zhao, X.L., Fernando D., Al-Mahaidi R., CFRP strengthened RHS subjected to transverse end bearing force, ‘‘Engineering Structures’’, Vol. 28(11), 1555–1565, 2006. [9] Lesani, M., Bahaari, M.R., Shokrieh, M.M., Experimental investigation of FRP-strengthened tubular T-joints under axial compressive loads, ‘‘Construction and Building Materials’’, Vol. 53, 243-252, 2014. [10] Lesani, M., Bahaari, M.R., Shokrieh, M.M., FRP wrapping for the rehabilitation of Circular Hollow Section (CHS) tubular steel connections, ‘‘Thin-Walled Structures’’, Vol. 90, 216-234. 2015. [11] Health and Safety Executive (UK), 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, 1997. [12] ABAQUS/CAE Standard user’s manual-Version 6.14-1, 2014. [13] Ganesh, K., Naik, N.K., ‘‘Some strength studies on FRP laminates’’, Journal of Composite Structures, Vol. 24, pp. 51-58, 2005. [14] AWS (American Welding Society), Structural welding code, AWS D 1.1:2010 (22nd Edition), Miami, FL (USA), American Welding Society, Inc, 2010. [15] N’Diaye, A., Hariri, S., Pluvinage, G., Azari, Z., Stress concentration factor analysis for notched welded tubular T-joints, ‘‘International Journal of Fatigue’’, Vol. 29, 1554-1570, 2007. [16] IIW-XV-E, International institute of welding sub-commission 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.