Flexural behavior of RC beams strengthened by natural flax FRP plates

This paper reports an experimental investigation on flexural strengthening of RC beams with natural flax fabric reinforced polymer (FFRP) composite plates. The experimental variables considered are FRP thickness (4 and 6 layer), the internal steel rebar ratio (0.223% and 0.503%) and the pre-cracking of RC beams (i.e. by applied 80% yielding load of control RC beam before the application of FFRP plates). This study shows that FFRP plates strengthening increased load, deflection and ductility of RC beams remarkably. The enhancement in load and ductility is more pronounced for RC beams with lower steel ratio. All the FFRP strengthened RC beams exhibited a similar failure pattern, namely, initial steel yielding and then rupture of the FRP plates. There was no obvious effect of pre-cracking on the load of the FFRP strengthened RC beams, showing that the effectiveness of FFRP external strengthening materials for retrofitting damaged RC beams (e.g. after earthquake-attack). In addition, the experimental results are compared with the predictions based on the equations given in ACI 440.2R-08 for beams strengthened with synthetic FRP composites. Copyright © 2016 Department of Civil and Environmental Engineering & Research Institute for Sustainable Urban Development, The Hong Kong Polytechnic University.