Experimental and analytical study on flexural strengthening of reinforced concrete beams using near-surface mounted ductile materials

The ductile performance of reinforced concrete (RC) structures is one of the crucial structural properties which define their deformability. This paper investigates the flexural performance of RC beams strengthened with near-surface mounted (NSM) prestressing screw-thread bar (PSB) under four-point bending. The effects of strengthening beams with NSM PSB on cracking behavior, failure modes, load-deflection relationships, and strains were obtained and discussed. Test results show that the NSM PSB strengthening system worked well with the surrounding concrete, effectively inhibited the propagation of cracks, and moderated the brittle failure of the strengthened beams. The load-bearing capacity of these strengthened beams was improved with the increase in prestressing level and NSM reinforced ratio. In addition, an analytical model was put forward to theoretically predict the load-bearing capacity and deflection of the strengthened beams, and the calculation results achieved good agreements with the experimental results. Besides, a database consisted of 42 RC beams strengthened by various methods with different ductile materials were collected from previous studies, and the assessment results validate the accuracy and feasibility of the proposed model.