A criticism on strengthening glued laminated timber beams with fibre reinforcement polymers, numerical comparisons between different modelling techniques and strengthening configurations


  • Dilan Çankal Department of Civil Engineering, Manisa Celal Bayar University, Manisa (Turkey)
  • Gökhan Şakar Department of Civil Engineering, Dokuz Eylül University, Izmir (Turkey)
  • Hüseyin Kürşat Çelik 3 Graduate School of Natural and Applied Sciences, Dokuz Eylül University, Izmir (Turkey)




Glued laminated timber beam, CFRP, strengthening, FEM, modelling.


The application of CFRP for strengthening timber structures has proven its efficiency in enhancing load-bearing capacity and, in some cases, the stiffness of structural elements, thus providing cost-effective and competitive alternatives both in new design and retrofitting existing historical buildings. In this study, glued laminated timber beams strengthened with CFRP were examined. A number of test beams with different reinforcement configurations and beam sizes were selected from the literature. These beams were analysed with three different methods as numerical, theoretical and code perspective. For the numerical method, a 3D nonlinear finite element model which includes damage and fracture mechanics was constructed. All test beams were studied with different methods and results were compared with respect to initial flexural stiffness, midspan vertical displacement and failure load. The effectiveness of methods and strengthening configurations were stated and suggestions for practical application of FRP-strengthened timber beams were presented.


Abrate, S. (2008). Criteria for yielding or failure of cellular materials. Journal of Sandwich Structures and Materials, 10(1), 5-5. https://doi.org/10.1177/1099636207070997

ACI Committee 440. (2017). Guide for the design and construction of externally bonded FRP systems for strengthening concrete structures. Farming Hills, Michigan, U.S.A.

Alhayek, H., & Svecova, D. (2012). Flexural stiffness and strength of GFRP-reinforced timber beams. Journal of Composites for Construction, 16(3), 245-252. https://doi.org/10.1061/(ASCE)CC.1943-5614.0000261

Ali, Y. A. Z. (2018). Flexural behavior of FRP strengthened concrete-wood composite beams. Ain Shams Engineering Journal, 9(4), 3419-3424. https://doi.org/10.1016/j.asej.2018.06.003

Aloisio, A., Boggian, F., Sævareid, H. Ø., Bjørkedal, J., & Tomasi, R. (2023). Analysis and enhancement of the new Eurocode 5 formulations for the lateral elastic deformation of LTF and CLT walls. Structures, 47, 1940-1956. https://doi.org/10.1016/j.istruc.2022.11.129

American Wood Council. (2015). NDS National Design Specification for Wood Construction: With Commentary. American Wood Council, USA.

ANSYS C. (2011). User manual Release 12.1. ANSYS Inc.

Aydın, I., Çolak, S., Çolakoǧlu, G., & Salih, E. (2004). A comparative study on some physical and mechanical properties of Laminated Veneer Lumber (LVL) produced from Beech (Fagus orientalis Lipsky) and Eucalyptus (Eucalyptus camaldulensis Dehn.) veneers. Holz Als Roh-Und Werkstoff, 62(3), 218-220. http://doi.org/10.1007/s00107-004-0464-3

Bakalarz M. M., Kossakowski, P.G. (2022). Ductility and stiffness of laminated veneer lumber beams strengthened with fibrous composites. Fibres 10(2). https://doi.org/10.3390/fib10020021

Bodig, J., & Jayne, B. A. (1982). Mechanics of wood and wood composites. Van Nostrand Reinhold, New York.

Borri, A., Corradi, M., & Grazini, A. (2005). A method for flexural reinforcement of old wood beams with CFRP materials. Composites Part B: Engineer-ing, 36(2), 143-153. https://doi.org/10.1016/j.compositesb.2004.04.013

BSI. (2009). BS EN 338: 2009. Structural timber-strength classes.

Bulleit, W. M., Sandberg, L. B., & Woods, G. J. (1989). Steel-reinforced glued laminated timber. Journal of Structural Engineering, 115(2), 433-444. https://doi.org/10.1061/(ASCE)0733-9445(1989)115:2(433)

Computers and Structures Inc. (2015). SAP2000 v15. Integrated Finite Element Analysis and Design of Structures.

Corradi, M., Mouli Vemury, C., Edmondson, V., Poologanathan, K., & Nagaratnam, B. (2021). Local FRP reinforcement of existing timber beams. Com-posite Structures, 258, 113363. https://doi.org/10.1016/j.compstruct.2020.113363

Dagher, H. J., Kimball, T. E., Shaler, S. M., & Abdel-Magid, B. (1996). Effect of FRP reinforcement on low-grade eastern hemlock glulams. In Proceedings of the National Conference on Wood in Transportation Structures, 207-214.

Danielsson, H., & Gustafsson, P. J. (2014). Fracture analysis of glued laminated timber beams with a hole using a 3D cohesive zone model. Engineering Fracture Mechanics, 124-125, 182-195. https://doi.org/10.1016/j.engfracmech.2014.04.020

Dietsch, P., & Winter, S. (2012). Eurocode 5—future developments towards a more comprehensive code on timber structures. Structural Engineering International, 22(2), 223-231. https://doi.org/10.2749/101686612X13291382991001

Dietsch, P. (2016). Reinforcement of timber structures–a new section for Eurocode 5. In Proceedings of the World Conference on Timber Engineering WCTE 2016, Vienna, Austria.

Donadon, B. F., Mascia, N. T., Vilela, R., & Trautwein, L. M. (2020). Experimental investigation of glued-laminated timber beams with Vectran-FRP reinforcement. Engineering Structures, 202, 109818. https://doi.org/10.1016/j.engstruct.2019.109818

European Committee for Standardization. (2004). Eurocode 5: Design of Timber Structures - Part 1-1: General - Common rules and rules for buildings, Brussels.

Fiorelli, J., & Dias, A. A. (2003). Analysis of the strength and stiffness of timber beams reinforced with carbon fibre and glass fibre. Materials Research, 6(2), 193-202. https://doi.org/10.1590/S1516-14392003000200014

Fiorelli, J., & Dias, A. A. (2011). Glulam beams reinforced with FRP externally-bonded: Theoretical and experimental evaluation. Materials and Structures, 44(8), 1431-1440. https://doi.org/10.1617/s11527-011-9708-y

Fortino, S., Zagari, G., Mendicino, A. L., & Dill-Langer, G. (2012). A simple approach for FEM simulation of Mode I cohesive crack growth in glued lami-nated timber under short-term loading. Journal of Structural Mechanics, 45(1), 1-20.

Gáborík, J., Gaff, M., Ruman, D., Záborsky, V., Kašíčková, V., & Sikora, A. (2016). Adhesive as a factor affecting the properties of laminated wood. BioResources, 11(4), 10565-10574.

Gentile, C., Svecova, D., & Rizkalla, S. H. (2002). Timber beams strengthened with GFRP bars: development and applications. Journal of Composites for Construction, 6(1), 11-20. https://doi.org/10.1061/(ASCE)1090-0268(2002)6:1(11)

Gilfillan, J., Gilbert, S., & Patrick, G. (2001). The improved performance of home-grown timber glulam beams using fibre reinforcement. Journal of the Institute of Wood Science, 15(6), 307-317.

Glišović, I., Pavlović, M., Stevanović, B., & Todorović, M. (2017). Numerical analysis of glulam beams reinforced with CFRP plates. Journal of Civil Engineering and Management, 23(7), 868-879. https://doi.org/10.3846/13923730.2017.1341953

Glišović, I., Stevanović, B., Todorović, M., & Stevanović, T. (2016). Glulam beams externally reinforced with CFRP plates. Wood Research, 61(1), 141-154.

Gustafsson, P. J. (2003). Fracture perpendicular to grain–structural applications. In T. Sh. J. Larsen (Ed.): Timber Engineering, John Wiley & Sons Ltd., pp. 103-130.

Haiman, M., & Žagar, Z. (2002). Strengthening timber glulam beams with FRP plates. In Wood in Construction Industry: Prospectives of Reconstruction. International Conference Proceedings, Zagreb, Croatia, 25-34.

Hill, R. (1948). A theory of the yielding and plastic flow of anisotropic metals. Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 193(1033), 281-297. https://doi.org/10.1098/rspa.1948.0045

Hoseinpour, H., Valluzzi, M. R., Garbin, E., & Panizza, M. (2018). Analytical investigation of timber beams strengthened with composite materials. Con-struction and Building Materials, 191, 1242-1251. https://doi.org/10.1016/j.conbuildmat.2018.10.014

İşleyen, Ü. K., Ghoroubi, R., Mercimek, Ö., Anil, Ö., & Erdem, R. T. (2021). Behavior of glulam timber beam strengthened with carbon fibre reinforced polymer strip for flexural loading. Journal of Reinforced Plastics and Composites, 40(17-18), 665-685. https://doi.org/10.1177/0731684421997924

Issa, C. A., & Kmeid, Z. (2005). Advanced wood engineering: glulam beams. Construction and Building Materials, 19(2), 99-106. https://doi.org/10.1016/j.conbuildmat.2004.05.013

Johns, K. C., & Lacroix, S. (2000). Composite reinforcement of timber in bending. Canadian Journal of Civil Engineering, 27(5), 899-906. https://doi.org/10.1139/l00-017

Khelifa, M., Auchet, S., Méausoone, P. J., & Celzard, A. (2015). Finite element analysis of flexural strengthening of timber beams with Carbon Fibre-Reinforced Polymers. Engineering Structures, 101, 364-375. https://doi.org/10.1016/j.engstruct.2015.07.046

Kim, Y. J., & Harries, K. A. (2010). Modeling of timber beams strengthened with various CFRP composites. Engineering Structures, 32(10), 3225-3234. https://doi.org/10.1016/j.engstruct.2010.06.011

Lacroix, D. N., & Doudak, G. (2018). Experimental and analytical investigation of FRP retrofitted glued-laminated beams subjected to simulated blast loading. Journal of Structural Engineering, 144(7), 04018089. https://doi.org/10.1061/(ASCE)ST.1943-541X.0002084

Lee, I. H., Song, Y. J., Song, D. B., & Hong, S. I. (2019). Results of delamination tests of FRP- and steel-plate-reinforced larix composite timber. Journal of the Korean Wood Science and Technology, 47(5), 655-662. https://doi.org/10.5658/WOOD.2019.47.5.655

Lee, M. J., Cho, T. M., Kim, W. S., Lee, B. C., & Lee, J. J. (2010). Determination of cohesive parameters for a mixed-mode cohesive zone model. Interna-tional Journal of Adhesion and Adhesives, 30(5), 322-328. https://doi.org/10.1016/j.ijadhadh.2009.10.005

Li, Y. F., Xie, Y. M., & Tsai, M. J. (2009). Enhancement of the flexural performance of retrofitted wood beams using CFRP composite sheets. Construction and Building Materials, 23(1), 411-422. https://doi.org/10.1016/j.conbuildmat.2007.11.005

Lu, W., Ling, Z., Geng, Q., Liu, W., Yang, H., & Yue, K. (2015). Study on flexural behaviour of glulam beams reinforced by Near Surface Mounted (NSM) CFRP laminates. Construction and Building Materials, 91, 23-31. https://doi.org/10.1016/j.conbuildmat.2015.04.050

McConnell, E., McPolin, D., & Taylor, S. (2014). Post-tensioning of glulam timber with steel tendons. Construction and Building Materials, 73, 426-433. https://doi.org/10.1016/j.conbuildmat.2014.09.079

Meier, U. (1995). Strengthening of structures using carbon fibre/epoxy composites. Construction and Building Materials, 9(6), 341-351. https://doi.org/10.1016/0950-0618(95)00071-2

Micelli, F., Scialpi, V., & la Tegola, A. (2005). Flexural reinforcement of glulam timber beams and joints with carbon fibre-reinforced polymer rods. Journal of Composites for Construction, 9(4), 337-347. https://doi.org/10.1061/(ASCE)1090-0268(2005)9:4(337)

Morales-Conde, M. J., Rodríguez-Liñán, C., & Rubio-De Hita, P. (2015). Bending and shear reinforcements for timber beams using GFRP plates. Con-struction and Building Materials, 96, 461-472. https://doi.org/10.1016/j.conbuildmat.2015.07.079

National Research Council of Italy. (2007). Guidelines for the design and construction of externally bonded FRP systems for strengthening existing struc-tures, Rome.

Raftery, G. M., Harte, A. M., & PR, And. (2009). Bonding of FRP materials to wood using thin epoxy glue lines. International Journal of Adhesion and Adhesives, 29(5), 580-588. http://dx.doi.org/10.1016/j.ijadhadh.2009.01.004

Raftery, G. M., & Harte, A. M. (2011). Low-grade glued laminated timber reinforced with FRP plate. Composites Part B: Engineering, 42(4), 724-735. https://doi.org/10.1016/j.compositesb.2011.01.029

Raftery, G. M., & Harte, A. M. (2013). Nonlinear numerical modelling of FRP reinforced glued laminated timber. Composites Part B: Engineering, 52, 40-50. http://dx.doi.org/10.1016/j.compositesb.2013.03.038

Systèmes, D. (2012). Abaqus/Standard Version 6.12-2. Computer program. Dassault Systèmes Simulia Corp. Providence.

Theiler, M., Frangi, A., & Steiger, R. (2013). Strain-based calculation model for centrically and eccentrically loaded timber columns. Engineering Structures, 56, 1103-1116. https://doi.org/10.1016/j.engstruct.2013.06.032

Thorhallsson, E. R., Hinriksson, G. I., & Snæbjörnsson, J. T. (2017). Strength and stiffness of glulam beams reinforced with glass and basalt fibres. Com-posites Part B: Engineering, 115, 300-307. https://doi.org/10.1016/j.compositesb.2016.09.074

Timbolmas, C., Bravo, R., Rescalvo, F. J., & Gallego, A. (2022). Development of an analytical model to predict the bending behavior of composite glulam beams in tension and compression. Journal of Building Engineering, 45, 103471. https://doi.org/10.1016/j.jobe.2021.103471

Tran, V. D., Oudjene, M., & Méausoone, P. J. (2014). FE analysis and geometrical optimization of timber beech finger-joint under bending test. Interna-tional Journal of Adhesion and Adhesives, 52, 40-47. http://dx.doi.org/10.1016/j.ijadhadh.2014.03.007

Wacker, J. P., & Groenier, J. (2010). Comparative analysis of design codes for timber bridges in Canada, the United States, and Europe. Transportation research record, 2200(1), 163-168. http://dx.doi.org/10.3141/2200-19

Wang, C. M., Reddy, J. N., & Lee, K. H. (2000). Shear deformable beams and plates: relationships with classical solutions. Elsevier Science Ltd. https://doi.org/10.1016/B978-0-08-043784-2.X5000-X

Yahyaei-Moayyed, M., & Taheri, F. (2011). Experimental and computational investigations into creep response of AFRP reinforced timber beams. Com-posite Structures, 93(2), 616-628. https://doi.org/10.1016/j.compstruct.2010.08.017

Yang, H., Liu, W., Lu, W., Zhu, S., & Geng, Q. (2016). Flexural behavior of FRP and steel reinforced glulam beams: Experimental and theoretical evalua-tion. Construction and Building Materials, 106, 550-563. http://dx.doi.org/10.1016/j.conbuildmat.2015.12.135



2023-12-31 — Updated on 2023-12-31


How to Cite

Çankal, D., Şakar, G. ., & Kürşat Çelik, H. . (2023). A criticism on strengthening glued laminated timber beams with fibre reinforcement polymers, numerical comparisons between different modelling techniques and strengthening configurations. Revista De La Construcción. Journal of Construction, 22(3), 661–678. https://doi.org/10.7764/RDLC.22.3.661