Bending performance of RC beams reinforced with UHPFRC strips with different geometry and positions

Abstract

Ultra‐high‐performance fiber‐reinforced concrete (UHPFRC) is one of the most favorable materials for strengthening RC beams. Studies on UHPFRC strengthening of RC beams mainly address flexural behavior. Further research is needed on key factors, such as UHPFRC‐to‐beam bond and system cost linked to strip geometry. This research studies experimentally and theoretically the possibility of strengthening the RC beams by combining a strip of UHPFRC to the bottom surface of some specimens or the bottom and top surfaces together for others. The study focused on three key variables to assess the effectiveness of UHPFRC strengthening strips: placement (bottom side only or both sides), length of the bottom strip relative to the total beam length (0.50, 0.60, and 0.80 L), and presence or absence of concrete cover on the bottom side before casting the UHPFRC strip. The results for a load‐deflection response, crack propagation, stiffness, and energy dissipation were used to compare other strengthened specimens. Eight strengthened specimens, divided into three series, were tested through a 4‐point loading regime to consider the effects of different parameters. Results revealed that strengthened beams on the bottom and top sides showed remarkably enhanced ultimate load, stiffness, and energy dissipation. UHPFRC strip length and removal of concrete cover were the most significant parameters. Moreover, extending the strip length from 1000 to 1200 mm shifted failure from shear to bending, increasing stiffness by 29% and load capacity by 23%, while deflection and energy dissipation were less affected. Further increasing the strip length to 1600 mm boosted load capacity and stiffness by 38% and 75%, while deflection and energy dissipation dropped by 21% and 31%. Finally, a numerical analysis was presented to investigate the influence of numerous parameters that might influence the bending performance of strengthened RC beams.