Structural reinforcement of bi-directional oak-wood lamination by carbon fibre implants

• Published in: Construction & building materials 2021-06, Vol.287, p.123073, Article 123073
• Main Authors: Novosel, Andrija, Sedlar, Tomislav, Čizmar, Dean, Turkulin, Hrvoje, Živković, Vjekoslav
• Format: Article
• Language: English
• Subjects: Carbon fibre reinforced polymer (CFRP); Digital image correlation (DIC); Ductility; Effective stiffness; Four-point bending; Laminated timber; Oak-wood
• ISSN: 0950-0618; 1879-0526
• DOI: 10.1016/j.conbuildmat.2021.123073

•Twofold increase in ultimate load to failure and stiffness.•Pre-stressing the implants in tension significantly contributed to strength.•Effective stiffness increased by up to 94%.•Increase in ductility of up to 14%. A study of the effect of implants made of carbon fibre reinforced polymer (CFRP) on improving the flexural stiffness of oak-wood model beams laminated in two directions was performed with the goal of improving stiffness in the elastic region, bending strength and overall ductility. Six compositions of implants (resin only, CFRP in various numbers of layers) were introduced in both the tensile and compression zone of the model beams, and some CFRP implants were introduced as pre-tensioned elements. This should enable the modelling of structural elements according to their mechanical requirements depending on the required properties of the final product (construction element, grid member, window, or curtain wall framing, etc.). Displacement and deformations were recorded during four-point bending tests using a 3D video extensometer and were analysed by digital image correlation (DIC). An analysis of the different systems of reinforcements shows that the effective stiffness (EI) and the ultimate load to failure (ULF) can be significantly improved by different types of implants, resulting in an improvement of between 4 and 94% for EI and of 2 and 106% for ULF. Generally, increasing the number of CFRP layers led to an increase in strength and stiffness and a change of ductility of up to 14% which is a sound improvement for the serviceability limit state. A significant reduction in the bending deformation may be obtained by introducing implants, but the effect is not proportional to the number of layers and associated costs. The smallest deformation was obtained on the beam reinforced with 21 layers of CFRP. However, even one or two layers of pre-stressed fibres led to significantly reduced deformations comparable to beams reinforced with multiple carbon layers.