REPAIRING AND STRENGTHENING OF RC BEAMS USING THIN LOWER CONCRETE LAYER REINFORCED BY FRP BARS

This paper presents the test results of an experimental study that investigates the behavior of reinforced concrete (RC) beams strengthened or repaired in flexure by adding thin lower concrete layer reinforced mainly by Fiber Reinforced polymers (FRP) bars. A total of seventeen RC beams were constructed and tested under fourpoint loading. One of these beams was un-strengthened and considered as a reference beam. Eight beams were strengthened in flexure, and the other eight beams were loading up to 70% from the ultimate load of reference beam and then repaired using the same methods provided to the strengthened beams. Five test parameters were considered in this research; status of beam (strengthened or repaired), type of reinforcement used (glass FPR, carbon FPR or steel), amount of reinforcing FRP bars used (2 bars or 4 bars), type of the strengthening technique (reinforcing bars installed in the adding concrete layer or FRP sheets externally bonded to the soffit of the adding concrete layer) and type of connection between the adding lower concrete layer and the original beam (installing dowels bars or not). The test results included ultimate load, cracking load, the corresponding deflection, the failure modes and calculated relative ductility and flexure stiffness at un-cracked and cracked stages. The percentage enhancement in the flexural capacity of the tested beams ranged from 32% to 106% compared with the reference beam. Using FRP bars showed greater ultimate load and more ductile behavior than using externally FRP sheets. Many failure modes were observed during testing; FRP rupture, FRP debonding or partial debonding between the adding concrete layer and the original beam depending on the method of strengthening or repairing had been applied to the tested beams. The experimental ultimate strength for all strengthened and repaired beams were compared with the design provisions provided by ACI 440-2R-08, which showed reasonable and lightly conservative predictions for all strengthened and repaired beams