Experimental and numerical analysis of the structural response of FRP-strengthened cold-formed steel columns

This paper reports the results of an experimental and numerical investigation on the non-linear behavior and load-carrying capacity of CFRP-strengthened cold-formed steel lipped channel columns. The experimental program involved two test series, comprising a total of 19 short and long fixed-ended lipped channel columns − while the former buckle in local-plate modes, the latter exhibit distortional buckling. The columns were strengthened with carbon fiber sheets glued at different outer surface locations (web, flanges or lips) and having fibers oriented either longitudinally or transversally − since the aim of the study is to assess the influence of the CFRP sheets on the column structural response, bare steel specimens were also tested. The experimental results, which consist of non-linear equilibrium paths (applied load vs. axial shortening) and ultimate strength values (most of them associated with local-plate and/or distortional failure mechanisms), are subsequently used to calibrate and validate geometrically non-linear numerical analyses based on shell finite element models, carried out with the code ABAQUS and adopting an elastic-plastic constitutive law to describe the steel material behavior. Finally, on the basis of both the experimental and numerical results obtained, some relevant conclusions are drawn concerning the most effective CFRP sheet location and fiber orientation to strengthen columns affected by local-plate and distortional buckling.