Flexural performance of reinforced concrete beams strengthened with prestressed FRP sheets: Experiments and numerical investigations

Previous experimental and analytical investigations have highlighted the efficacy of employing prestressed fiber-reinforced polymer (FRP) sheets to enhance the flexural performance of reinforced concrete beams under specific design conditions. This research aims to broaden the understanding by conducting experiments and numerical simulations to provide more comprehensive insights into the performance of FRP sheet-strengthened beams, encompassing a wide array of design parameters. Initially, four reinforced concrete beam specimens undergo experimental testing, comprising three scenarios strengthened with CFRP sheets exhibiting varying levels of prestress. Subsequently, 42 experimentally validated numerical simulation models are employed for the parametric analysis of the strengthened beams. Considered design parameters include the material properties, dimensions, and prestress levels of FRP sheets, as well as the concrete strength and geometric characteristics of the beams. Experimental and simulation results show that strengthening with prestressed FRP sheets significantly enhances the flexural performance of reinforced concrete beams, including delaying the onset of flexural cracking and steel reinforcement yielding. The greater the prestress levels, dimensions, and elastic modulus of the FRP sheets, the more pronounced this effectiveness becomes, and they are still maintained with increases in the dimensions and strength of the concrete of the reference beam. Conversely, the ultimate load of the beam is notably influenced by the bond between the FRP layer and the concrete. Increasing the stiffness or prestress levels of FRP sheets may accelerate delamination due to increased horizontal shear stress on the concrete-FRP interface, making the ultimate load of the beam less significant. Therefore, to increase the ultimate load of the beam by using prestressed FRP sheets, the prerequisite is to enhance the bond between the FRP sheets and the beam using high-strength adhesives or other mechanical bonding approaches.