STIFFNESS OF GLUED WOODEN BEAMS WITH COMBINED REINFORCEMENT

Abstract

Due to the dynamic development and use of glued timber structures, there is a need for comprehensive research. In particular, increasing the strength of such structures by means of reinforcement is a pressing issue. Recent studies have shown good prospects for using synthetic fiber-based composites to improve the properties of wooden structures. The development and availability of synthetic fibers have made composite reinforcement effective in reinforcing glued wood elements. The purpose of this work is to investigate the stiffness of glued wooden beams reinforced with different types of reinforcement in the compressed and stretched zone. Two series of beams were prepared for research. All beams had a rectangular cross section of 100x150 mm and  was 3 m long. The first series included two glued unreinforced beams. They were tested to determine the fracture load, to establish control deflections and to compare them with the corresponding deflections of reinforced beams.  The second series included two glued reinforced beams. They were reinforced with a 12 mm diameter steel rod in the compressed zone and a Sika CarboDur S-512 carbon fiber tape in the stretched zone. Due to the combined reinforcement, an attempt is made to increase the stiffness and bearing capacity of the glued wood elements under flexural loading. The test specimens were loaded using a jack by two concentrated loads. The deflections of all beams were measured using the deflection indicators that were installed above the supports, in the middle of the span and additionally under concentrated loads. After processing the obtained data, comparative graphs of the variation of deflection versus bending moment were constructed. As a result of research, the data on the flexural behavior of glued timber beams with combined reinforcement were obtained for the first time. Allowable deflections for reinforced glued timber elements were achieved at a flexural load of 12.5 kNm, which was more than 1.5 times greater than the bending moments of beams without reinforcement. The deflections of unreinforced beams at each load level were on average 60% higher than the deflections of reinforced beams at the same load level.