Shear performance of yellow meranti solid timber beam strengthened using fibre reinforced polymer

Abstract

Yellow Meranti timber has relatively lower shear strength than other softwood species due to its shorter fibre length and larger pores. As a result, it suffers lower fibre strength, more brittle and lower load carrying capacity. In some cases the timber beams experience shear failure that occurs suddenly right before bending. Thus, shear strengthening for Yellow Meranti by using Fibre Reinforced Polymer (FRP) is crucial to solve the aforementioned problems for the structural application. This research was conducted to improve the shear performance of Yellow Meranti beam by strengthening it with carbon fibre reinforced polymer (CFRP) plates, CFRP laminate and glass laminate (GFRP) using Sikadur-30 and Sikadur-330 as bonding agents and for laminating. Firstly, materials characterization was conducted for the timber, FRP and adhesives, to determine their mechanical properties on shear, tensile and compression. The bonding between the FRPs to the timber using epoxy adhesives was examined and the effective bond length was determined. Thirty-six beams with dimension 100 mm x 200 mm x 1475 mm were tested, where three of the beams were un-strengthened and used as the control beam. The remaining beams were strengthened with various configurations and tested under four-point loading up to failure. The results showed that all the strengthened beams perform better than the control beam in terms of ultimate load, shear strength, stiffness and ductility. The performance enhancement by FRP to timber beam for load carrying capacity and shear capacity was ranged from 11.0% to 41.0%, while for stiffness; the range was 26.61% to 62.05%. The ductility index for strengthened beams ranged between 2.0 to 3.7 and 3.7 to 8.4 based on deflection and energy method respectively. The optimum number of FRP is 5 strips which was equivalent to 0.45 strengthened area ratio (Af /Ashear). The optimum type of FRP was GFRP. However types of FRP did not give significant difference in shear strengthening. FRP orientation angle of 45° was found to be the optimum angle in this study. The optimum wrapping schemes were by fully wrapped (FW) with addition of FRP overlapping at the bottom of the beam. Strengthening at the shear zone of the beam could change the mode of failure from shear failure to combination of compression and tensile fracture with no shear failure at shear zone. All the predicted shear capacities computed in this study have good agreement with the experimental value where the percentage difference ranged from 0.5% to 18.3%. As a conclusion, the shear performance of solid beam of Yellow Meranti timber was successfully improved by external strengthening using FRP, where the optimum design parameter for shear strengthening was proposed. As a result, the modification factors formula for shear strength and stiffness were proposed. The result of this study is also able to assist both researchers and engineers in the field of timber engineering technology in the tropical countries to perform strengthening work on timber beams.