Effective Stiffness of Reinforced Concrete Columns

Existing and proposed models of the effective stiffness of reinforced concrete columns subjected to lateral loads are assessed using the experimental response of 329 concrete columns. Existing models appropriate for design applications tend to overestimate the measured effective stiffness and are unacceptably inaccurate, because they generally neglect the influence of anchorage slip on the effective stiffness of the column. A three-component model that explicitly accounts for deformations due to flexure, shear and anchorage-slip is shown to provide a more accurate estimate of the measured effective stiffness for the database columns. This model is simplified by neglecting small terms and approximating the results of moment-curvature analysis to obtain an accurate and rational effective stiffness model appropriate for design applications. For this model, the ratio of the measured stiffness to the calculated stiffness had a mean and coefficient of variation of 1.02 and 22% for circular columns and 0.95 and 25% for rectangular columns.