Experimental and numerical study of the parameters controlling the behavior of double-lap connections of steel plates bolted to hybrid FRP strips

Fiber-reinforced polymers (FRP) are increasingly being used in strengthening existing structures. The bonding technique for strengthening steel structures was found to be associated with the brittle failure of the adhesive. In 2012, researchers validated the use of bolted hybrid FRP (HFRP) in strengthening steel beams. The current study aims to investigate a wide spectrum of test parameters to compile a reliable database on the interfacial behavior of bolted HFRP–steel connections. An extensive experimental program was carried out on forty-two double-lap HFRP–steel bolted connections under tensile loading. Test parameters included the number of washers, clamping torque, diameter of hole, and spacing of bolts. Results recommend snug-tight bolts to be installed in standard size holes with the use of two washers per bolt. Experimental measurements are utilized to develop a multi-linear load-slip model that can be integrated in finite-element models to facilitate the analysis of this particular type of connection.