Mechanically fastened hybrid composite strips for flexural strengthening of concrete beams

• Novel mechanically-fastened FRP flexural reinforcing developed for reinforced concrete.
• Reinforcing system is easy to install and cost-effective.
• Flexural tests indicate reinforcing provides strength gains of nearly 50%.
• Environmental and fatigue durability were experimentally assessed.

While externally bonded fiber-reinforced polymer reinforcing has become an accepted technology for the flexural strengthening of reinforced concrete members, less information is available on flexural strengthening using mechanically fastened FRP (MF-FRP). This study presents the development of a vacuum-infused, hybrid glass–carbon MF-FRP system for the flexural strengthening of reinforced concrete beams. Two different FRP fabric architectures were considered to assess the impact of fiber orientation on behavior. The resistance of the MF-FRP composite strips to freeze–thaw cycling and saltwater submersion was assessed with single-fastener tension–bearing testing. Test results indicate that the MF-FRP system should display adequate residual capacity in typical cold-climate bridge applications. The flexural strengthening capabilities of MF-FRP composite strips were evaluated using four-point bending tests of MF-FRP-strengthened, steel-reinforced concrete beams and non-strengthened beams. The flexural test results for two glass–carbon MF-FRP reinforcing systems show an average increase in ultimate capacity of nearly 50% with good ductility. Flexural fatigue testing was conducted on four MF-FRP reinforced specimens. The cyclic flexural test results indicate that the strength gains that can be realized with the MF-FRP systems used here may be limited by fatigue performance, and that fatigue is an area that warrants further study.