Flexural Behavior of an RC Beam Externally Strengthened with a Steel- and CFRP-Based Method

Reinforced concrete beam bridges are usually retrofitted by a steel plate or FRP. However, these two methods tend to result in disadvantages, e.g., construction complexity and debonding failure, owing to the corresponding material properties. In this study, a steel- and CFRP-based method is proposed to achieve the merits of typical retrofitting methods by combining a CFRP plate, a steel plate, and angle steel. To investigate the effect of the cooperative strengthening, six full-scale beam specimens were designed and are evaluated through a monotonic four-point bending test. The failure mode, load–deflection relationship, critical parameters, and crack development are systematically and sequentially analyzed. Finally, a predicting method is proposed to calculate the flexural capacity. The retrofitted beam is characterized by an acceptable load-bearing capacity and deformation capacity. With continuous retrofitting, the crack load and ultimate load can be improved up to 84.9% and 4.41 times, respectively. The steel plate and angle steel function in both the load bearing and the anchorage to the CFRP plate contributes more to the ultimate bearing capacity after the steel components yield. Finally, a calculating model is shown to accurately predict the ultimate bearing capacity after retrofitting, with an average error of 4.03%.