Mechanically-fastened hybrid composites for flexural strengthening of steel beams

Recent experimental studies by Sweedan et al. [17] and Alhadid et al. [2] on the behavior of mechanically fastened (MF) steel-FRP lap connections and steel beams strengthened with MF-FRP, respectively, revealed a promising efficiency of the fastening system in retrofitting deteriorated steel beams. The study demonstrated that the dominant failure mode, in the tested connections and beams, was due to excessive bearing in the FRP laminate at the locations of the fasteners as long as sufficient number of fasteners is used. The current study describes a three-dimensional nonlinear finite element (FE) model that accounts for the interfacial slip between the FRP laminates and the steel beam. The FE model is validated against the experimental results reported by Alhadid et al. [2], and excellent agreement is found. The FE model is then used to shed more light on the mechanical behavior of the tested composite steel-FRP beams including force distribution in steel fasteners especially during spread of yielding in the steel section, and the stress distribution in the FRP laminates. The study concludes that as the length of the FRP increases, the degree of composite action in the elastic range increases indicating higher efficiency of the FRP laminate. The FRP laminate contributes significantly in carrying the mid-span loads after yielding of the steel section.