Analytical Design Model for Reinforced-Concrete Beams Strengthened in Shear Using L-Shaped CFRP Plates

Abstract

This paper presents the results of an analytical study on reinforced concrete (RC) T-beams strengthened in shear with L-shaped fiber-reinforced polymer (FRP) plates. The main objective of this study is to develop design equations for RC beams retrofitted in shear using L-shaped FRP plates, considering all possible modes of failure in ultimate limit states. Unlike RC beams strengthened with externally bonded (EB) FRP plates and fabrics, prefabricated L-shaped plates feature unconventional failure modes because of their special shape and anchorage. The possible failure modes for RC beams strengthened with L-shaped FRP plates are (1) concrete breakout at the embedded part of the FRP plate in the flange; (2) FRP pull-off at the epoxy/FRP interface; (3) FRP pull-off at the concrete/epoxy interface; and (4) FRP overlap failure at the beam soffit. These failure modes do not occur in RC beams shear-strengthened with EB FRP fabrics and plates. Therefore, the existing design models for EB FRP fabrics and plates cannot predict with sufficient accuracy the contribution of FRP to the shear resistance of RC beams shear-strengthened with L-shaped plates. In this article, new design equations are proposed in light of recent developments and data. These equations distinguish the failure mode and calculate the FRP contribution to the shear resistance of RC beams strengthened with L-shaped FRP plates. In some cases, full embedment of the L-shaped carbon FRP (CFRP) plates in the RC beam flange is not feasible because of the presence of an obstacle (e.g., longitudinal reinforcing steel bars in the flange). The new design equations are applicable to RC beams strengthened with L-shaped FRP plates with different embedment lengths (including no embedment) of the CFRP plates in the RC beam flange. The proposed design equations are validated against experimental data collected from the literature.