Numerical and analytical investigation of square timber columns confined with steel and carbon fiber reinforced polymer external jacket

This paper numerically investigated the timber confinement of columns with carbon fiber reinforced polymer (CFRP) and steel tubes under axial compression. An elastic-plastic model with linear hardening, a CFRP hashin damage, and a timber damaged anisotropic elastic-plastic model, respectively, are used to simulate the inelastic behavior of the steel tube, CFRP layers, and timber core. In addition, a comprehensive numerical study was conducted using a wide range of cross-sections, thicknesses, lengths, and the number of CFRP layers developed to varying degrees (0, 45, and 90). To confirm the accuracy of the current FEM model, numerical data is compared to the experimental model’s final strengths, behavior, and failure mechanisms. Additionally, the ultimate strengths of timber-steel and CFRP are compared to various standards and design formulas. The results reveal that columns with thicker steel tubes and more CFRP layers have an average of about 42% and 12% greater load-bearing capacity and ductility. The degree of CFRP affected the load-bearing capacity of timber columns, which increased by around 10% from 45 to 90. In comparison to specimens with equal cross-sections and thickness, shorter specimens with greater cross-sections typically have 40% higher stiffness. According to parameter studies, the AISC 360-16 American standard design approaches can be safely extended to anticipate the ultimate strength of timber-steel columns. Meanwhile, both the ACI-440 and Ilki et al. design formula predictions are the most precise, particularly at 45° with high ultimate strength.