Research on Arch Effect and CFRP Strengthening Effect of RC Beams with Corroded Stirrups

Abstract

In many cases the corrosion of steel reinforcement is considered to be the main reason that leads to the deterioration of the bond between steel reinforcement and concrete and causes the failure of members. However, stirrups with smaller diameter are more likely to get rusted and it is more difficult to find corrosion expansion cracks on the surface of concrete. Then the function of stirrups to restrict longitudinal bar from slipping will be weakened, which alters the mechanical properties and failure mode of corroded Reinforced Concrete (RC) beams. In this paper, the influence of corrosion of stirrups and the effect of strengthening corroded RC beams with Carbon Fiber Reinforced Polymer (CFRP) sheets were studied. The corrosion rate for each group varied between 0% to 18% which represented mass loss of the longitudinal steel reinforcement on the tension side. The longitudinal reinforcement of beams in Group A was not wrapped by the stirrups in order to simulate the situation that the stirrups were seriously corroded and lost their function. Beams of Group B were corroded control beams. Beams of Group C were corroded and then repaired by applying longitudinal CFRP sheets at the bottom and additional U-shaped CFRP sheets around the cross-section. Test results showed that the corrosion of stirrups had a detrimental effect on strength as well as the bond stress between steel bars and concrete. The mechanical mode of experimental beams tended to act like an arch. The greater the corrosion rate was, the more obvious the arch effect was. In addition, combining longitudinal and U-shaped CFRP sheets enhanced the ultimate load by an average of 56.5% of corroded RC beams. However, because of the longitudinal cracks, the strengthening effect of CFRP was much diminished when the corrosion rate was particularly high.