Mechanical repair of timber beams fractured in flexure using bonded-in reinforcements

The flexural properties of strength class C16 spruce beams have been compared to the flexural properties of the same beams repaired with bonded-in reinforcements in the form of steel or composite pultruded rods. Reinforcing materials included rectangular sections of mild steel, pultruded carbon fibre reinforced plastic (CFRP), glass fibre reinforced plastic (GFRP) and a thermoplastic matrix glass fibre reinforced polyurethane (FULCRUM). Grooves were routed into the faces of the fractured beams following straightening and the reinforcements adhesively bonded into the top, bottom or both faces of the beams. The steel and CFRP reinforcements are most effective in restoring the flexural strength which often exceeds its original value. These reinforcements are also effective in enhancing flexural strength but the CFRP reinforcement endows the greatest transformed flexural strength. The fracture mechanisms in the repaired beams depend on the placement of reinforcement and the quality of the adhesive to reinforcement bond. All properties are optimised by bonding reinforcement into both faces of the fractured beams.