A review on strengthening of timber beams: Materials and methods in the NSM technique

Timber has been used in buildings for hundreds of years because of its good mechanical and thermal insulation properties as well as its energy-absorbing ability. Timber structures need careful attention during service life because of decaying and aging. Therefore, the timber structural elements have been modified with traditional and modern techniques. This study comprehensively reviewed the materials and methods in timber strengthening and highlights the importance of timber materials and the applied strengthening methodologies in the near surface mounted (NSM) technique. It critically compares different parameters including the reinforcement and bonding materials, timber types, criteria for beam dimensions, application and curing conditions, groove dimension and reinforcement positioning, moisture, and temperature effects. In addition, this study proposes the detailed applied methodology for NSM technique while identifying the key research gaps and clear future directions to successfully enhance the structural performance of timber elements. It was found that approximately 600 timber beams across 25 wood species were evaluated with a wide range of strength grades of 14–70 MPa, and a density between 290 and 900 kg/m 3 . While, the moisture content of specimens varied between 10% and 18%, temperature of 18–30 °C. It is also concluded that the replicates for control specimens should not be less than five, and careful attention should be given to the curing process of the selected adhesive for better bonding.