Tensile Strengthening of Full-Scale Timber Beams with Mechanically Attached GFRP Composite Plates

Results of bending tests aimed at improving the flexural behaviour of the timber beams reinforced with GFRP (Glass Fiber Reinforced Polymer) composite plates externally attached using mechanical joints are presented in this paper. Modest ratios of GFRP composite reinforcement can increase beam load-carrying capacity and manipulate failure mode from brittle tensile in the unreinforced beam to a more extensible failure in the strengthened timber beams. Application of mechanical joints presents a solution of reversibility, compatibility and durability for reinforced timber. The experimental campaign focuses on load-deflection relationship and failure modes in order to increase the loading capacity and stiffness of the timber beam. Oak beams with dimensions 145 x 145 x 2450 mm were reinforced with un-bonded pultruded GFRP plates. Speciality coach screws 16 mm diameter, 130 mm length, grade 8.8, were used to reversibly attach the reinforcement with fender washers having outer diameter 34 mm to distribute the load away from the screw position. All beams were tested until failure under the four-point bending arrangement. Experimental results demonstrate the effectiveness of the reinforcement method and ability to reversibly repair timber, representing a capability to be utilised in the new construction or restoration of timber structures.