STRESS-STRAIN RELATIONSHIP OF SHORT CIRCULAR TIMBER COLUMNS STRENGTHENED BY A COMPOSITE METHOD IN AXIAL COMPRESSION

The composite reinforcement method with near surface mounted steel bars and wrapped CFRP (carbon fiber reinforced polymer) strips can effectively improve the strength and deformation capacity of historical timber columns. To establish the stress-strain model of strengthened timber columns, 42 timber columns strengthened by the composite reinforcement method were tested under axial compression, taking the number of wrapped CFRP strips and near surface mounted steel bars as the experimental factors. The test results indicated that the composite reinforcement method can improve the ductility and compressive strength of the timber columns. Because of the inevitable initial defects of timber, the failure of timber columns mainly occurred in the area where the initial defects concentrated. The load-strain curves of timber, CFRP strips and steel bars were consistent at the same measurement point, which showed that there were good bond properties between the timber and CFRP strips or steel bars, so that they can deform and work together. According to the existing researches, the formulas of peak stress and peak strain of the strengthened timber columns were given by fitting the experimental data. Trilinear and polynomial constitutive models of strengthened timber columns under axial compression were proposed. Considering the discreteness of timber material, the theoretical model curves were consistent with the test curves. It verified the reliability of the obtained stress-strain models.