Analytical approach for the flexural analysis of RC beams strengthened with prestressed CFRP

Abstract

a b s t r a c tThe objective of this paper is to propose a simplified analytical approach to predict the flexural behavior of simply supported reinforced-concrete (RC) beams flexurally strengthened with prestressed carbon fiber reinforced polymer (CFRP) reinforcements using either externally bonded reinforcing (EBR) or near surface mounted (NSM) techniques. This design methodology also considers the ultimate flexural capacity of NSM CFRP strengthened beams when concrete cover delamination is the governing failure mode. A moment-curvature (M-v) relationship formed by three linear branches corresponding to the precracking, postcracking, and postyielding stages is established by considering the four critical M-v points that characterize the flexural behavior of CFRP strengthened beams. Two additional M-v points, namely, concrete decompression and steel decompression, are also defined to assess the initial effects of the prestress force applied by the FRP reinforcement. The mid-span deflection of the beams is predicted based on the curvature approach, assuming a linear curvature variation between the critical points along the beam length. The good predictive performance of the analytical model is appraised by simulating the force-deflection response registered in experimental programs composed of RC beams strengthened with prestressed NSM CFRP reinforcements.

Flexural performance of reinforced concrete beams strengthened with prestressed near-surface-mounted FRP reinforcements

“…When releasing the prestressing force, an initial compression field in the longitudinal steel bars and surrounding concrete is introduced [10,25,26]. As the external loads increase, these compressive strains are converted to tensile strains.…”

Transfer zone of prestressed CFRP reinforcement applied according to NSM technique for strengthening of RC structures

“…The model takes into account the strain profile of the beam's cross section due to the negative camber created after the release of the prestress force (using the model proposed by [24]), as an initial condition (designated by superscript symbol of (ci)) for the strains in the constituent materials.…”

“…In fact, when the prestress force ( pre F ) is released, an initial negative camber (upward deflection) is obtained due to the eccentricity ( e ) of this prestress force in relation to the centroidal axis of the cross section ( i y ) (Figure 7) [24].…”

“…) in the CFRP reinforcement assuming proportionality of the strain distribution along the cross section, as represented in Figure 7 [24]. This short-term prestrain loss and effective tensile strain ( ( ) ci ef ε ) in the CFRP reinforcement immediately after total release of the prestress force are determined from the following equations: Using Eqs.…”

“…(A1) -(A5) are derived by assuming no cracking occurs after the release of the prestress force (Figures 5 and 7). A more detailed description of the analytical model reported in Appendix A can be found elsewhere [24,35].…”