Experimental and theoretical study on flexural behavior of prestressed concrete beams strengthened by CFRP tendons with external unbonded retrofit system

The considerable age of many prestressed concrete (PC) beams, coupled with a steadily increasing amount of traffic and evolving design concepts, have underscored the importance of maintenance and retrofitting over the years. The use of prestressed carbon fiber reinforced polymer (CFRP) has emerged as an effective method for reinforcing deteriorated beams. This study established a new external unbonded retrofit system employing CFRP tendons for the structural reinforcement of prestressed concrete beams. The flexural behavior of a series of PC beams with length of 4300 mm was tested via four-point bending experiment. One PC beam served as reference beam without any strengthening measures, while three beams were strengthened using prestressed CFRP tendons with varying diameters (7 mm and 10 mm) and prestress levels (15 %, 30 %, and 50 %). The experimental results demonstrated that the cracking loads and ultimate loads of the strengthened beams exhibited a significant increase compared to those of the reference beam, up to 53.8 %. Additionally, a theoretical model was proposed to calculate the flexural resistance of prestressed CFRP-strengthened beams, which exhibited a good agreement with the experimental results. This study provided a guidance for the application of PC beams reinforced with external prestressed CFRP tendons and developed an accurate theoretical model for predicting the flexural resistance of reinforced beams.