Experimental Investigation of Axial Compression in Composite Strengthened Historical Timber Columns

This work explores the effectiveness of composite strengthening for historical timber columns, which strengthens the timber columns with near surface mounted steel bars and wrapped CFRP strips. Different numbers of steel bars and two approaches for attaching CFRP strips were compared in tests of 36 timber columns. The failure modes, ultimate load, and ductility of specimens were analyzed. The stress-strain curves and deformation compatibility of each component of specimens were discussed. The results indicate that the composite strengthening effectively enhances the ductility and bearing capacity of strengthened timber columns. Pre-tensioned CFRP strips performed better than the epoxy-bonded CFRP strips in improving the bearing capacity and compression elastic modulus, but not in enhancing deformation performance. Analysis of the strain comparison curves showed that the embedded steel bars and timber can work together in deformation, and that the wrapped CFRP strips can restrain timber columns' lateral expansion. Overall, reliable and effective strengthening was achieved using the proposed reinforcement method. Finally, according to fitting analysis and related theories about CFRP confined concrete columns, a calculation model of peak loads for strengthened timber columns was established. The reliability of the newly proposed model was verified through the comparison between theoretical and experimental values.