Flexural Stiffness of Reinforced Concrete Columns and Beams: Analytical Approach

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Title: Flexural Stiffness of Reinforced Concrete Columns and Beams: Analytical Approach

Author(s): Madhu Khuntia and S. K. Ghosh

Publication: Structural Journal

Volume: 101

Issue: 3

Appears on pages(s): 351-363

Keywords: beam; column; flexural stiffness; moment

Date: 5/1/2004

Abstract:
The present ACI code (ACI 318-02) provisions on effective stiffnesses of beams and columns are reviewed. Factors influencing the moments of inertia of beams and columns are discussed. The primary variables considered are: the reinforcement ratio, the axial load ratio, the eccentricity ratio, and the compressive strength of concrete. On the basis of a parametric study, simple formulas are proposed to determine the effective stiffnesses of reinforced concrete columns and beams. The proposed stiffness expressions are applicable for all levels of applied loading, including both service and ultimate loads. The analytical results show that the flexural stiffness assumption in the current ACI code procedure for design of slender columns using the moment magnifier method (Eq. (10-11) and (10-12)) is extremely conservative. Recommendations are made concerning stiffness assumptions in the analysis of reinforced concrete frames under lateral loads.