Non-linear behaviour and load-carrying capacity of CFRP-strengthened lipped channel steel columns

This paper reports the results of an experimental and numerical investigation on the non-linear behaviour and load-carrying capacity of CFRP-strengthened cold-formed steel lipped channel columns, devoting special attention to their local-plate and/or distortional buckling behaviours. A preliminary GBT-based study concerning the column elastic buckling behaviour is performed, focusing on determining the (i) sheet location (web, flanges and/or lips) and (ii) carbon fibre orientation (longitudinal, transverse or inclined) that optimize the strengthening procedure (enhanced buckling behaviour vs. cost). Then, an experimental programme comprising a total of 19 short and long fixed-ended lipped channel columns is described. The columns were strengthened with carbon fibre sheets (CFS) bonded at different outer surface locations (web, flanges or lips) and having the fibres oriented either longitudinally or transversally — since the aim of the study is to assess the influence of the CFS 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 and physically non-linear numerical analyses based on shell finite element models and carried out in the code Abaqus. Finally, on the basis of both the experimental and numerical results obtained, some relevant conclusions are drawn concerning the most effective CFS location and fibre orientation to strengthen lipped channel steel columns affected by local-plate and/or distortional buckling.