Flexural Stiffness of Reinforced Concrete Columns and Beams: Experimental Verification

The current ACI code 318-02 provisions on effective stiffnesses of beams and columns have been reviewed in a companion paper, in which simple formulas are proposed to determine the effective stiffnesses of reinforced concrete columns and beams, based on an analytical parametric study. Analytical axial load-bending moment diagrams of slender columns for a given initial eccentricity (M/P ratio), obtained using the proposed stiffness assumptions, are compared in this paper with numerous published test data and are found to be in good agreement. The proposed stiffness expressions are applicable for all levels of applied loading, including both service and ultimate loads. Analytical and experimental results show that the flexural stiffness assumption in the current ACI code procedure for design of slender columns using the moment magnifier method (Eq. 10-12 and 10-18) is extremely conservative.