Modeling of axially loaded hss slender steel members retrofitted with composites

This paper describes an analytical model developed to predict the behaviour of axially loaded slender members composed of steel hollow structural sections (HSS), retrofitted with carbon-fibre reinforced polymer (CFRP) composite sheets. A previous experimental study by the authors showed that gain in strength due to CFRP retrofitting was highly sensitive to the specimen's imperfection. As such, developing an analytical model was necessary to uncouple the effects of imperfection and number of CFRP layers. The model predicts the load versus axial and lateral displacements, and accounts for steel plasticity, the built-in through-thickness residual stresses, geometric non-linearity, including initial imperfection, and the contribution of CFRP sheets. The model was verified against results of the experimental program and showed reasonable agreement. The model was then used in a parametric study. The study demonstrated that retrofitting slender HSS columns using CFRP sheets increased both the axial strength and stiffness substantially.