Analysis and design of FRP reinforced concrete columns

Analytical investigations of rectangular concrete compression members reinforced with fiber reinforced polymer (FRP) reinforcing bars were carried out based on the ACI ultimate strength approach. The strength interaction (P-M) relations of reinforced concrete columns with FRP bars were examined and compared to columns with steel bars. The results identified the possibility of premature-compression and brittle-tension failures which were related to the compression and tension ruptures of FRP bars. Brittle-tension failure, when compared with premature-compression failure, was more likely to occur due to low ultimate tensile strain of FRP bars. The study also concluded that the ACI minimum reinforcement ratio limit for steel reinforced concrete columns was not adequate for use in FRP reinforced concrete columns. In this study, design aids have been developed for FRP rectangular concrete columns to determine the minimum required reinforcement ratio (ρ_f,min) for averting the brittle-tension failure to a failure controlled by concrete crushing; a failure concept used for steel reinforced concrete columns. The proposed approach using ρ_f,min enabled the analysis and design of concrete columns reinforced with FRP bars to be carried out in a manner similar to columns reinforced with steel bars based on the ACI 318-05 provisions.