Strengthening of Prestressed Concrete Beams Using Prestressed NSM CFRP Bars to Enhance Structural Performance

In this study, prestressed concrete beams were strengthened using the NSM strengthening technique with CFRP bars which were prestressed using a pretensioning method. Seven prestressed beams were tested under monotonic four-point loading, with one unstrengthened control beam, one beam strengthened with a non-prestressed NSM CFRP bar and five beams strengthened with NSM CFRP bars prestressed to 30%, 40%, 50%, 60% and 70% of their nominal tensile strength. The effect of prestress level in the NSM CFRP bar on beam structural behavior and failure mode was investigated. The results indicated that prestressing the NSM CFRP bar increased first crack, yield and ultimate loads while decreasing deflection compared to unstrengthened and non-prestressed strengthened beams. The strengthened beams failed by CFRP bar rupture. The structural performance of the 70% prestressed strengthened beam showed the greatest enhancement, with first crack and ultimate loads increasing by 43% and 47%, respectively, over the control beam.