Natural fibres have recently raised attention for presenting adequate mechanical characteristics for the reinforcement of wood structural elements. The use of both natural fibres, in laminated beams and wood from reforestation, is in accordance with the current economic interest and sustainable appeal. This paper focuses on the analysis the viability of sisal fibre use, in wood laminated structures as a reinforcing material, taking three methods into consideration: Stress functions, Classical lamination theory and Transformed section method. The laminated beams were reinforced by sisal strips with a thickness of 2 mm and constituted by the species of wood: Pinus (Pinus sp). Each lamina has the following dimensions: width of 5 cm, height of 10 cm and length of 150 cm. It was noted that the differences between the results from the classical lamination theory and transformed section method were, in an average of 14 % and 16 % for normal and shear stresses respectively. The difference of 12 % for displacements is a normal result taking into account that the span used is considered high for this wood species. In relation to the stress function method, the differences are minimal, around less than 1% for all analyses. It was also noted that the beam with reinforcement presented a decrease of the values of normal and shear stresses and displacements in relation a beam without reinforcing fibres. This decrease was of the order of 8% for the normal and 5% for the shear stresses and 12 % for the displacements In general, the strengthening of wood laminated beams with sisal fibres is more effective for structures that are used only in wood structural elements, in which the elastic modulus is at least equal to these fibres.
