Replacement of Conventional Steel Stirrups by Internal Reinforcing CFRP Grids in Shear of Concrete Beams

Abstract

This study proposes an innovative idea of shear reinforcement in concrete beam by replacing the conventional steel stirrups with CFRP grids at the shear span inside concrete cover. The compatibility between the internal grids and the surrounded concrete was investigated first in the elementary test. Flexural performances of two concrete elements reinforced by different spacing of internal grids were compared and discussed. After that, a concrete beam test was conducted with a total of eight RC beams varied in the number of grid strips in the shear span and the spacing of reinforcing grids. The experimental results showed that the shear capacity and the shear carried by internal CFRP grids significantly improved with a higher amount of grid strips; however, the increasing ratio of shear capacity was not proportional to the shear reinforcement ratio. Moreover, the location of internal grid in the shear span was an important part of the shear-resisting effectiveness in this study since the more number of grid strips located near the center of the shear span was much more effective to resist the propagation of diagonal shear crack than the grids at the edge. Finally, a model for evaluating shear carried by internal CFRP grids was introduced. Validity of the proposed model was explained by comparing with the experimental results and also other sets of experimental results.