Interaction diagram methodology for design of FRP-confined reinforced concrete columns

This paper presents a procedure that allows the construction of a simplified axial load – bending moment interaction diagram for FRP-wrapped Reinforced Concrete (RC) columns of circular and non-circular cross-sections for practical design applications. In the proposed methodology, the analysis of FRP-confined columns is carried out based on principles of equilibrium and strain compatibility equivalent to that of conventional RC columns, the primary difference being the use of the stress–strain model for FRP-confined concrete developed by Lam and Teng. Based on the consideration that the strength enhancement is of significance in members where compression is the controlling failure mode, only the portion of the interaction diagram corresponding to this type of failure is the focus of the methodology. Experimental evidence from RC specimens with a minimum side dimension of 300 mm (12 in.) and subjected to combined axial compression and flexure was collected and compared to the theoretical interaction diagrams. Even though limited experimentation has been conducted in the compression-controlled region for such type of members, data points appear to be consistent with the analytical predictions. A design method for RC members is therefore proposed following the principles of the ACI building code.