Strengthening reinforced concrete beams with prestressed near surface mounted fibre reinforced polymers

The work done in this thesis investigates the effect of using an innovative anchorage/prestressing system that is capable of strengthening concrete beams using prestressed Near-Surface-Mounted (NSM) technique. The effect of the newly developed prestressing system on the behaviour of the concrete beams under various prestressing levels was studied. The developed system proved to be an easy and practical method to prestress the NSM CFRP reinforcement. Two types of Carbon Fibre Reinforced Polymers (CFRP) profiles (rebar and strips) were used in the tests. A total of nine beams were tested, one beam was considered unstrengthened control beam for the comparison purpose, the other eight beams were classified into two groups each contains four beams. The first group was strengthened with two CFRP strips while the second group was strengthened with one CFRP rebar. Beams in each group were prestressed into various prestressing levels (0%, 20%, 40% and 60%) of the ultimate tensile strength of the CFRP material. Results showed that all beams strengthened with prestressed CFRP failed due to rupture in the FRP without any premature failure gaining an increase in the ultimate capacity up to 68% compared to the unstrengthened control beam. In addition, the deflection of the beams decreased while the cracking and the yielding loads increased significantly due to prestressing effect. This shows the effectiveness of the contribution of the new prestressing system with reinforced concrete beams strengthened FRP NSM technique.