The majority of the current provisions on slender column design first appeared in the 1971 version of ACI 318 as a result of the recommendations of ACI-ASCE Committee 441, Reinforced Concrete Columns. In the figure, the major steps of the slender column provisions are shown as they relate to each analysis method.įigure 1: Summary of ACI 318-11 column provisions. Figure 1 presents a summary of the current ACI 318-11 provisions for slender concrete columns. The two methods use different base values for stiffness, and then each apply different reduction factors to the stiffness values. The main source of these inconsistencies can be attributed to the approximation of a column’s flexural stiffness, EI. But the question remains, “Why is there such a large difference within the provisions?” As a result, engineers often discount the moment magnification procedure in favor of the more manageable results obtained from an elastic second order analysis. Simply put, moments estimated by the moment magnification procedure may be upwards of five times larger than those estimated by a second order analysis. These inconsistencies cause confusion amongst practitioners and result in wide variations in their use and/or interpretation. Considerable inconsistencies can exist between the results obtained from an elastic second order analysis and the moment magnification procedure. The provisions in the moment magnification procedure allow for a column to be designed using a conventional first order analysis provided that the moments calculated by the analysis are increased to account for second order effects. In contrast, engineers would evaluate a non-slender or short column using an elastic first order analysis.
PCA COLUMN SOFTWARE CODE
If a column is slender, engineers must consider either an elastic second order analysis or they may analyze the column by the moment magnification procedure contained within the Building Code Requirements for Structural Concrete (ACI 318-11). Typically, second order effects of this magnitude occur when a column is slender that is, when its height-to-width ratio is greater than approximately 10. When designing a column, structural engineers must evaluate the impact of second order or P-∆ effects to determine if loads applied to a structure in its deformed position significantly increase internal forces (i.e.
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