Impact of anchored holes technique on behavior of reinforced concrete beams strengthened with different CFRP sheet lengths and widths

The premature de-bonding failure, of the carbon fiber reinforced polymer (CFRP) composites, is among the most important problems that hinder external strengthening utilizing CFRP sheet. Although it is recommended to use the end anchorage systems to address this important issue, it is needed to further explore the impact of those systems on enhancing the flexural performance of strengthened reinforced concrete (RC) beams. Therefore, most interest is focused on the feasibility of using the anchored holes to improve the behavior of RC beams. The proposed anchored technique includes the preparation of the bonding surface of each concrete beam. Later, the anchoring holes have been drilled using a rotary drill at the end of the bonded area. Seventy four RC beams were used to conduct the experimental program. Seventy two of those samples were externally strengthened by a CFRP sheet. The investigated parameters, in this study, were: the length of CFRP sheets, the width of CFRP sheet, and number of anchored holes. The performance characteristic of each tested beam was evaluated in terms of load versus each of: the mid-span deflection curve, failure mode, ultimate load capacity, ultimate deflection, displacement ductility index, stiffness, energy absorption, energy absorption ductility index, performance factor, and CFRP strain. The study results showed a significant improvement in the majority of the investigated parameters. The results, also, showed that the behavior of the tested beams was more effective when using anchored holes combined with CFRP strengthened beams. This improvement is due to the efficient anchored holes in providing external cracks arresting mechanism after steel reinforcement yielding and cracking and even after reaching the ultimate load capacity. Finally, the efficiency of the adopted end anchored holes system in enhancing ductility in flexural-strengthened RC beams is explored in detail.