Experimental and Numerical Investigation of the Behavior of Steel Beams Strengthened by Bolted Hybrid FRP Composites

The strengthening of steel beams using hybrid fiber-reinforced polymers (HFRPs) has gained enormous attention over the last decades. Few researchers have investigated the effectiveness of the fastening techniques without a bonding agent to overcome the undesirable debonding failure of the bonded FRP–steel system. This paper reports the outcomes of experimental and numerical investigations conducted on steel beams strengthened by HFRP using steel bolts. Twenty-two steel beams were tested in four-point loading to investigate the effect of the HFRP length and the bolt arrangement on the flexural behavior of the strengthened systems. The observed failure modes, load-deflection relations, deflection profiles, and strain measurements were also studied. The tested beams showed a ductile behavior, with 15.1 and 22.2% enhancements in the yield and ultimate flexural capacities, respectively. Simplified empirical equations were developed to predict the ultimate load of the bolted HFRP–steel beams. ANSYS software was used to model the beams’ behavior and investigate the effects of the HFRP thickness, bolt spacing, steel grade, loading scheme, and beam length on the effectiveness of the adopted fastening technique. Increasing the HFRP length enhanced the utilization of HFRPs as well as the beam’s ductility, with a reduction of up to 51.2% in the mid-span deflection. Moreover, the strain compatibility of the HFRP–steel beams was improved with an 87.2% reduction in the interfacial slippage. The bolt arrangement showed an insignificant effect on the overall performance of the beams. The numerical results verified the effectiveness of the fastening technique in enhancing the flexural performance of the steel beams, with gains of up to 16.7% and 34.5% in the yield and ultimate load-carrying capacities, respectively.