Abstract
The paper represents the experimental work of strengthening prestressed concrete (PC) beams having strands ruptured at the midspan using externally bonded carbon fiber reinforced polymer (CFRP) sheets. The effects of different parameters as the sheet lengths, number of the bonded sheets and attaching schemes on the flexural performance were investigated. The flexural capacity of the strengthened beam having 50% ruptured strands was enhanced up to 167.3% compared to that of the undamaged PC beam. The outcomes exhibited that both the number of layers and the lengths of CFRP sheets affected the failure behaviors as well as the flexural capacity of the strengthened PC beams. The increase in the number of sheets resulted in the reduction of tensile stress resisted by the remaining prestressing strands. However, the increase in the number of sheets with insufficient sheet lengths did not provide a higher flexural strength because the failure mode was transformed from the debonding induced by the flexural cracks in the constant moment region to the debonding from the sheet ends. The increase in the sheet lengths not only prevented the latter failure but also significantly improved the beam stiffness. More importantly, the debonding of the sheets was avoided by wrapping the transverse sheets for the whole beam span. The prediction of the flexural strength of the strengthened PC beams based on the guidelines of ACI, JSCE and fib exhibited a good agreement with small total thickness of the bonded sheets. However, the equations in the guidelines were conservative when the total thickness of the bonded sheets was large.
