Numerical analysis for predicting the ultimate capacity of rectangular reinforced concrete stub columns

The ultimate capacity of confined concrete columns prediction requires nonlinear analysis. There are a number of studies that focus on the analysis of concentrically loaded columns where the highest confinement is utilized since the entire cross section is under confined compression. On the other hand, the area of effectively confined concrete is reduced when eccentric loads are applied due to the appearance of the tension zone. Accordingly, a new material model is developed that reduces the ultimate confined strength gradually from the fully confined value f_cc to the unconfined value f'_c as a function of the compression area to total area ratio. A numerical model is generated using the finite layer procedure and the secant stiffness approach, which loads the section concentrically and eccentrically gradually to achieve equilibrium points of P-ε and M-φ response up to failure. The algorithm develops Force-Moment failure interaction diagrams for unconfined and confined columns cases. The unconfined interaction diagrams are well compared to the commercial software, and the confined diagrams are benchmarked against experimental data.