Peeling-Versus-Shear Failures in Prematurely Collapsing RC Beams Strengthened in Flexure

Failure modes of flexurally strengthened reinforced concrete (RC) beams can be broadly classified into full-bond response and partial-bond response. Among these, peeling (premature failure) and shear-block failure are closely related and cause catastrophic collapse. Provisions in current design standards are largely generalized (too simplified or too complex), and tend to ignore some key parameters. In particular, design standards have not clearly characterized the effect of shear on the peeling. In this work, experiments and numerical studies have been conducted to investigate the shear-peeling failure and differentiate it from other failure modes. The results have been used to extend the existing design recommendations. The proposed design procedure and the finite element (FE) models are validated, and the outcome is compared with the literature. The comparison and the use of the Chi-squared test showed that the proposed design formulations are more appropriate for calculating the moment capacity and predicting the sequence of failure modes of plated RC beams.

Deterioration of the structure, an increased applied load, or an error in the design are only a few of the causes for the requirement for external strengthening. For example, the beams of many bridges and other constructed facilities urgently need strengthening (external reinforcement). After being retrofitted with fiber-reinforced polymer (FRP) or steel plate at the soffit, RC beams are vulnerable to various failure modes, including conventional failures and undesired early failures (such as plate debonding and peeling). The current design standards either include provisions that could be more generic (too simplistic) or more complicated for practitioners to utilize. Further, the focus is needed on some critical aspects and parameters that determine the failure type. For instance, since shear failure (not a premature failure type) and peeling (a premature failure type) may seem to be comparable in certain circumstances, it is essential that design guidelines accurately specify the influence of shear on the peeling. Although shear failure is also an abrupt failure, it is not uncertain. Therefore, this study provides handy guidelines (in the form of a graphic/diagram/chart) to help professionals evaluate existing structures that have undergone flexural strengthening in the past or to prevent or at least reduce the likelihood of such failures occurring during the design phase.