Static and free vibration analysis of RC beams with NSM CFRP rectangular rods

Abstract Among the methods available for repairing or strengthening reinforced concrete (RC) beams, the Near Surface Mounted (NSM) technique has been shown to be a suitable method in many cases. Nevertheless, the effect of tensile concrete cracking on the bond mechanisms of Fiber Reinforced Polymer (FRP) rods in rod-resin interfaces and/or in resin concrete interfaces has yet to be investigated. This paper analyses the effects of damages due to bending cracking of concrete and loss of bond of NSM carbon-FRP (CFRP) rectangular rods on the static and dynamic responses of strengthened RC beams. Occurrence of damage in a reinforced concrete element leads to changes in its dynamic response. In many cases, experimental vibration monitoring of strengthening through dynamic tests is a convenient, non-destructive method. An investigation was developed to evaluate the experimental vibration changes of RC beams; three beams were built and examined experimentally by static tests and free vibration. One non-strengthened beam was tested to evaluate frequency value changes due to cracking at increasing bending moment. Two beams were strengthened with NSM CFRP rectangular rods: one was built without defects and one was strengthened with an imposed damage simulating loss of adhesion damage. Comparison between experimental and theoretical frequency values for three beams and the analysis of frequency changes due to damage for bending cracks and loss of adhesion allow discussing the actual behavior of RC beams with NSM CFRP rods.