Experimental study on the flexural behaviour of timber beams strengthened with high ductility and low cost hybrid fibre sheets

Timbers with defects are often used in historical buildings. However, the existing fibre sheet reinforcing technology for the timber beams is difficult to balance the strength, ductility and cost. This paper aims to develop novel high ductility hybrid fibre sheets for strengthening timber beams at a lower cost than available methods. First, four types of unidirectional and two types of bidirectional fibre reinforced polymer (FRP) sheets were designed and evaluated using scanning electron microscopy (SEM) and tensile tests. Then, the FRP sheets were used to make 68 timber beams with square and round cross sections for bending tests. Finally, parameter analysis was conducted to evaluate the enhancement law of specimens with different sheet layers, fibre types, reinforcement angles and interlaminar hybrid modes. The results show that the reinforcement angle of a round timber beam has a great influence on its ultimate bearing capacity, for which the recommended value range is 45°∼60°. Unidirectional fibre sheets with a fibre ratio of carbon fibre:aramid fibre:glass fibre = 2:1:1 have a positive hybrid effect on bearing capacity and can improve the ultimate deflection of timber beams by 69.2–115.4% with one layer. These research results can contribute to state-of-the-art knowledge about round and square section timber beams strengthened with hybrid fibre sheets and the conservation of timber structures.