Both metallic, as well as fiber-reinforced polymer, reinforcement in the form of rods, laminates or mats were used. Previous attempts to apply internal reinforcement to wood structures included the introduction of reinforcement inserts into the tensile zone or into the tensile and compression zone-a more effective method. In the second case, the reinforcement is completely surrounded-this can be achieved by moving the reinforcement deep into the cross-section or by using additional wooden cover plates glued to the applied reinforcement. In this way, the outer layer of the adhesive is flush with the outer surface of the reinforced component. Near-surface mounted (NSM) fiber-reinforced polymer (FRP) reinforcement is done by hollowing out a groove, or grooves, within the cross-section perimeter in which the reinforcement inserts are then placed and an adhesive composition poured on. Due to the position of the reinforcement in relation to the original cross-section of the reinforced beam, the near-surface mounted and internal reinforcement should be distinguished. Reinforcing timber beams with glued-in fiber-reinforced polymer inside the cross-section provides an aesthetic external surface for the reinforced beam, exposing the structure of the timber and protecting the reinforcement against environmental factors. The strain profile reading showed a higher utilization of the compression characteristic of veneer in specimens reinforced with carbon laminates. The reinforced elements were characterized by a greater variation in failure mode, resulting from tension, compression or lateral torsional buckling. The failure of the reference beams was caused by exceeding the tensile strength of the LVL. Increases of 11% and 7% in the global modulus of elasticity in the bending and stiffness coefficients were achieved, respectively. The reinforcement mainly affected the enhancement of the maximum bending moment values evaluated at the points of application as having concentrated forces of 32% and 24% in comparison to the unreinforced elements. Two strips of carbon fiber-reinforced polymer (CFRP) reinforcement were glued into rectangular grooves in the component bottom with two-component epoxy resin (0.62% reinforcement percentage). Experimental tests were performed on full-scale beams made of laminated veneer lumber (LVL) with nominal dimensions of 45 × 200 × 3400 mm. The results of the experimental tests and a brief outline of the characteristics of the internal reinforcement of wood structures are presented.
The topic of the article is the analysis of the static work of unreinforced and reinforced with composite material timber beams under bending tests.
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