Shear behavior of reinforced concrete beams strengthened with a hybrid system combining externally bonded and embedded through-section methods

Abstract

Reinforced concrete (RC) structures are extensively utilized in the construction industry due to their numerous advantages. However, these structures can deteriorate over time. To address the need for strengthening and rehabilitating existing RC structures, the use of fiber-reinforced polymer (FRP) materials has become highly desirable. This study aims to enhance the shear performance of RC beams using a combination of embedded through-section (ETS) and externally bonded (EB) techniques with FRP composites. An experimental program involving eleven beams subjected to three-point bending tests was conducted to investigate various parameters, including types of FRP (carbon and glass), increased areas of strengthening systems, variations in strengthening schemes (U-wrap and side wrap), and types of adhesives (epoxy and bioresin). The study carefully examines beam behaviors such as shear capacity, strain in shear reinforcement (both steel stirrups and FRP), and failure mechanisms. The results demonstrated a significant enhancement in shear capacity by 15.6% to 78.2% with the hybrid EB-ETS strengthening method. In several instances, the hybrid strengthening method was able to delay premature debonding of the FRP sheet beyond the ACI limit of 4000 microstrain. Interestingly, the study found that increasing the width of FRP sheets did not proportionally increase shear resistance. Additionally, the viscosity of the adhesive affects the mechanical bonding properties of the beam, improving load capacity. Furthermore, the accuracy of existing shear models proposed in design guidelines and literature was evaluated. Utilizing a modified effective strain formulation improved predictive accuracy, aligning more closely with experimental data compared to the original models.