Theoretical and experimental investigations into flexural behavior of existing reinforced concrete beams strengthened by CFRP bars

Strengthening existing reinforced concrete (RC) beams using carbon fiber reinforced polymer (CFRP) bars have gained greater interest and increased field applications. Theoretical and experimental investigations have been conducted in this research to learn the flexural behavior of RC beams strengthened by CFRP bars. Bending tests were performed on seven specimens to obtain the load-displacement curves of the beams with different strengthening methods. Different features of the failure modes were observed in the bending tests. Strengthened beams by CFRP bars can significantly increase the flexural bearing capacity of RC beams and retard the development of cracks, which is an effective means to improve flexural stiffness. In addition, the experimental results revealed the influences of the bar connection mode. RC beams strengthened by continue bars have a greater ultimate load than those strengthened by lapped bars. A refined finite element (FE) model was built and validated by the experimental results. This validated FE model clarified the failure mode of beams from the perspective of displacement evolution and strain development. Furthermore, theoretical formulas were established to calculate the ultimate flexural capacity of the strengthened beams, which was proved to have acceptable accuracy in predicting the flexural behavior of the CFRP-strengthened beams. This research may provide a valuable reference for strengthening the existing RC beams.