Optimization and a new constitutive equation for RC beam strengthened by FRP

The use of FRP has been developed for flexural strengthening of reinforced concrete (RC) beams in recent years due to its advantages, such as ease of implementation, a slight change in cross-sectional dimensions, corrosion resistance, and increase in bearing capacity of the beam. Therefore, paying attention to technical considerations in applying FRP is crucial. This study intends to address two specific concerns. The first one is to determine the effect of the number of FRP layers on the improvement of mechanical and seismic properties in the flexural strengthening of RC beam and to specify the necessary numbers of FRP layers. The other consideration is to propose a new equation for FRP debonding stress and explain the behavior of FRP in tension after the occurrence of debonding failure. In this regard, reinforced concrete samples were prepared with zero, one, three, and five layers of GFRP, and then, four-point tests were performed on the samples. The results indicated an optimal number of GFRP layers that led to maximum mechanical and seismic properties in the flexural strengthening of beams. This study showed that the proposed model could not only estimate the debonding stress but also describe the behavior of GFRP after the debonding.