Experimental and Analytical Investigation of Behavior of RC Beams Strengthened by Prestressed CFRP Straps using NSM Method

The current study is focused on strengthening of reinforced concrete (RC) beams using CFRP straps installed in pre-cut grooves. The method which is referred as near surface mounted (NSM) benefits considerable advantages in comparison with the conventional externally bonded reinforcement (EBR) method and provides better normal and shear stress transfer between the FRP and concrete substrate. The advantages of NSM method compared to EBR are investigated in this paper from viewpoints of loading capacity، serviceability and better use of FRP materials. Five simply-supported RC beams were cast and tested in the laboratory of Department of Civil Engineering of Isfahan University of Technology (IUT). One of the beams was un-strengthened (base specimen) while one was strengthened without prestressing and the other three were strengthened with CFRP straps with prestress up to 5، 20، and 30 percents of the nominal capacity of the composite. The results revealed that the prestressed beams show higher values of cracking and yield loads compared to strengthened specimen without prestressing. The cracking loads for the specimens with 5، 20، and 30 percents prestressing were respectively 117%، 127. 5%، and 144. 5% higher than that of base specimen; while the cracks in prestressed strengthened specimens were more limited with smaller crack width. Furthermore، the strengthened beams by prestressed CFRP had higher ultimate loading capacities and their failures happened at smaller deflections. The ultimate loads for the specimens strengthened by CFRP prestressed up to 5، 20، and 30 percents of their ultimate capacity were 11. 5%، 14. 7%، and 15% higher، respectively، compared with that of base specimen.