Adhesive choice for near-surface-mounted reinforcement of wooden beams in historical buildings

Strengthening of existing timber members is important challenge to prevent demolition and reconstruction of existing structures. Heritage buildings often comprise old timber members that may need strengthening and retrofitting due to degradation, damage, or simply increase of applied load. Among available strengthening techniques, the use of near surface mounted (NSM) plates represents an attractive solution due to its low invasiveness, rapidity of installation, and effectiveness in improving the capacity of the strengthened member. Composite and stainless steel NSM plates are often adopted. However, due to the numerous differences among timber species and actual hygrothermal conditions of the member, selecting an adhesive able to provide a proper stress transfer between the plate and timber is fundamental. In this paper, 28 single-lap direct shear tests are performed to study the bond behaviour of carbon fibre-reinforced polymer (CFRP) and stainless steel plates near surface mounted within a larch substrate. One polyurethane and three epoxy resin adhesives are investigated. The results provide an insight into the bond behaviour of the NSM plates with varying the resin type.