Axial performance and failure analysis of repaired historic timber columns using carbon fiber-reinforced polymer and steel bolts

The preservation of historic timber structures is essential for cultural heritage conservation; however, structural degradation often necessitates reinforcement interventions. This study experimentally evaluates traditional bolted connections and modern carbon fiber-reinforced polymer (CFRP) reinforcement techniques for deteriorated timber columns obtained from three historic buildings. The experimental program consisted of 12 strengthened specimens and three reference specimens, in which damaged sections were replaced with new chestnut wood and reinforced using bolts (two, four, or six bolts) or CFRP layers (one, two, or three layers). Axial compression tests and digital image correlation analysis were conducted to assess load-bearing capacity, stiffness, energy dissipation capacity, and failure mechanisms. The results showed that, although both strengthening techniques improved structural performance, neither was able to fully restore the capacity of the intact specimens. Bolted connections enhanced stiffness but induced stress concentrations, whereas CFRP reinforcement improved ductility while exhibiting limitations related to interfacial adhesion. The findings highlight the challenges associated with preserving historic timber elements and provide valuable insights into the effectiveness of strengthening techniques as sustainable and minimally invasive strategies for the structural rehabilitation of heritage timber structures.