Análise do reforço com fibras de carbono no comportamento mecânico de vigas de LVL de madeira de paricá coladas com resina de poliuretano à base de óleo de mamona

Abstract

Paricá, a native Amazonian species and one of the pioneers in planted forest cultivation, is characterized by rapid growth, good workability, and low density. However, due to its low mechanical strength class (D20), the use of this wood species in structural elements of civil construction is limited. An alternative to overcome this limitation is its industrial processing into laminated veneer lumber (LVL) incorporating carbon fiber reinforcement. Among synthetic fibers, carbon fibers stand out due to their high elastic modulus and tensile strength, low density, high thermal stability, and good thermal and electrical conductivity. In this context, the present study aimed to evaluate the influence of unidirectional carbon fiber fabric reinforcement on the mechanical behavior of LVL beams manufactured from paricá veneers bonded with castor oil-based polyurethane, with the goal of improving the material’s mechanical properties and expanding its potential for structural applications. To this end, four series of elements were produced under laboratory conditions: solid sawn timber beams; unreinforced LVL beams; LVL beams reinforced with one layer of carbon fiber fabric; and LVL beams reinforced with two layers of carbon fiber fabric. In the reinforced series, the reinforcement was placed between the outermost and penultimate veneers on the tension side of the beams. The mechanical behavior of the beams was assessed through four-point bending tests, with the determination of maximum bending moment, global stiffness, ductility, and failure modes. Maximum bending moment and global stiffness were estimated using both analytical (transformed section method) and numerical (finite element method) approaches. Additionally, to assess the influence of reinforcement on the bond quality provided by the adhesive, shear tests at the glue line were conducted. The results showed that reinforcement with two layers of carbon fiber fabric led to significant increases in load-carrying capacity (27.16%) and stiffness (29.98%) of the LVL beams compared to unreinforced elements. In contrast, the application of only one layer resulted in limited gains in maximum bending moment, with no statistical significance, and was insufficient to increase the global stiffness of the beams. Moreover, compared to unreinforced elements, the use of reinforcement altered the failure modes from brittle to ductile, increasing ductility indices by up to 137.37% (for LVL reinforced with two layers), which may indicate enhanced structural safety. Both theoretical approaches proved effective in estimating the mechanical properties of the series, with the numerical method showing greater agreement with the experimental results when compared to the analytical method. In addition, the failure modes observed in the numerical model adequately represented those observed experimentally. The presence of reinforcement did not affect the bond quality provided by the polyurethane adhesive.