Long-term behavior of wide shallow RC beams strengthened with externally bonded CFRP plates

• The addition of CFRP plates has no significant effect in reducing the long term deflections.
• Increasing the sustained load level increased immediate and long term deflections of the beams.
• Effective modulus analysis was found to reasonably predict the long term deflection of the beams.
• The Gergely and Lutz equation can be used with the EMM to predict the long term crack width of the beams.

The use of fiber reinforced polymer (FRP) for flexural strengthening by adhesively bonding to the tension soffit of reinforced concrete (RC) beams has become a popular retrofit technique. Extensive research work is available in the literature on the short term behavior of RC beams strengthened with externally bonded FRP reinforcement. On the other hand, the long term behavior of FRP-strengthened beams has not yet been fully explored. This paper investigates the long term deflection and cracking characteristics of wide shallow RC beams strengthened with carbon FRP (CFRP) plates. Five full scale wide shallow beams were constructed: two beams were tested under static loading and three beams were tested under sustained load for a period of 600 days. Three of the beams were strengthened with CFRP plates bonded to the soffit of the beams and two beams were unstrengthened serving as control. The long term beam deflection was compared with the predictions of the effective modulus approach considering two different concrete creep models. Beams strengthened with CFRP plates showed significant improvement in the short term deflection and crack width compared to the unstrengthened beam. The strengthened beams, however, did not show that much improvement in the long term behavior. The effective modulus approach was found to reasonably predict the additional long term deflection of the beams depending on the incorporated concrete creep model. Further, an analytical procedure for predicting the long term crack width of the beams was presented.