Simplified Second-Order Analysis of Slender FRP-Reinforced Concrete Columns Using the Nominal Curvature Method

The nominal curvature method is one of the simplified methods for the second-order analysis of steel-RC columns in design codes. The two parameters that are important in the application of this method are the total curvature distribution factor and the nominal curvature. Generally, for steel-RC columns, nominal curvature can be reasonably estimated from the curvature of the cross section for a balanced failure and linear interpolation is performed for load values other than the balanced failure load. However, when fiber-reinforced polymer (FRP) bars are used as a reinforcement for concrete columns, the balance point may not appear in the load–moment capacity curve or may appear at a very low load value and not at the knee bend of the load–moment capacity curve. Due to such behavior of FRP bar-RC (FRP-RC) columns, the estimation of nominal curvature is complex. This work examines the application of the nominal curvature method for the second-order analysis of FRP-RC columns and presents an equation based on a parametric study to estimate the nominal curvature of FRP-RC columns. In addition, when applying the nominal curvature method, the total curvature distribution factor is normally assumed as 10, which may be unconservative in some cases. In this work, an equation is presented to reasonably estimate the total curvature distribution factor, both for steel-RC and FRP-RC columns. Furthermore, a worked-out example and load–moment capacity curves for cross-sectional analysis are presented for FRP-RC columns. The outcomes would be of benefit for developing the design standards for FRP-RC structures and the simplified second-order analysis of RC columns.