An experimental study on flexural strengthening of PC beams with ruptured strands using CFRP sheets

The degradation of prestensioned prestresssed concrete (PC) beams, which are due to the rupture of prestressing strands, causes an excessive reduction in flexural capacity. With the aims to recover the flexural strength of the damaged beams in which the strands were partially ruptured, the experiment was conducted. The strengthening method using externally bonded carbon fiber reinforced polymer (CFRP) sheets was adopted to strengthen the damaged beams having half of the prestressing strands were cut at the midspan. The flexural strength of the damaged PC beams decreased to 52% from that of undamaged PC beam. CFRP sheets with the same lengths were attached to the tension face for flexural strengthening with different number of layers and attaching schemes. The enhancement of flexural capacity up to 91.5% to that of the undamaged beam revealed the effectiveness of strengthening method. However, the increase in ultimate loads was not associated with increasing the number of layers. Furthermore, the amount of CFRP sheet layers affected the failure mode of the strengthened PC beams. The beam strengthened by one and two layers of CFRP sheets failed in debonding of CFRP sheets induced by flexural cracks, whereas, the beams bonded with greater amount of CFRP sheets failed due to debonding of the sheet ends though the same length of sheets was provided. Providing U-wrapped transverse sheet and changing attaching schemes provided higher cracking loads, however, were not sufficient in preventing the debonding from the sheet ends.