Flexural Performance of Steel Beams Strengthened by Fastened Hybrid FRP Strips Utilizing Staggered Steel Bolts

Flexural strengthening of steel structures by fastening fiber-reinforced polymers (FRPs) has been proposed by a few researchers to overcome the brittle de-bonding failure associated with the bonded strengthening technique. This paper investigates the experimental flexural performance of steel beams strengthened by fastening hybrid FRPs (HFRPs). Staggered steel bolts are used to attach the HFRP strips to the steel tension flange. Fourteen steel beams were tested in a four-point loading setup to examine their behavior under various bolt spacing values, HFRP lengths and HFRP thicknesses. All strengthened beams experienced ductile failure with yield load enhancement ranging between 5.22 and 11.73% and improvement in the ultimate load from 8.5 to 18.76%. Reducing the spacing between the bolts from 150 to 45 mm enhanced the ultimate load and the level of composite action between the fastened components. Doubling the HFRP length resulted in a slight increase in the ultimate load and a remarkable reduction in the mid-span deflection. Meanwhile, doubling the thickness of the HFRP revealed an insignificant effect on the beam’s ultimate load and composite action. The recorded sectional strains were used to analyze the level of composite action between the fastened elements.