Analytical and Theoretical Development of Load-Moment Interaction Diagrams of Rectangular CFRP-RC Columns

Carbon Fiber-Reinforced Polymer (CFRP) bars have several advantages over traditional steel reinforcement, including low density, erosion resistance, and higher tensile strength. The ACI 440.11-22 code permits CFRP as reinforcement; however, there are limited experimental studies on its application in Reinforced Concrete (RC) columns under combined loads. This study utilized theoretical analysis and Finite Element Analysis (FEA) to investigate 25 square slender concrete columns (kL/r = 17) affected by concentric and eccentric loads, examining variables, like CFRP bar contribution, eccentricity-to-depth ratio, and reinforcement arrangement. The results demonstrated CFRP's effectiveness in these columns, with failure modes varying from brittle compression-controlled under low eccentricities to tension-controlled under high eccentricities. The FEA results indicated that the CFRP columns exhibited higher second-order moments than the steel columns due to CFRP's lower elastic modulus, these results were compatible with the experimental results. Moreover; the (P-M) interaction diagram of CFRP reinforced column does not experience a balanced point. It was also observed that increasing the reinforcement ratio enhances the axial capacity by 33% and the bending resistance by 141% while reducing the ties’ spacing from 140 mm to 40 mm has no significant influence on both the axial capacity and bending resistance. The study also expanded to verify theoretical models against experimental data, confirming their accuracy. These findings contribute to establishing reliable design guidelines for CFRP-RC columns influenced by axial loads and bending moments.