Flexural Stiffness of Rectangular Reinforced Concrete Columns

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Title: Flexural Stiffness of Rectangular Reinforced Concrete Columns

Author(s): S. A. Mirza

Publication: Structural Journal

Volume: 87

Issue: 4

Appears on pages(s): 425-435

Keywords: building codes; columns (supports); flexural strength; moments; loads (forces); reinforced concrete; slenderness ratio; stiffness; statistical analysis; structural design; tied columns; Design

Date: 7/1/1990

Abstract:
The ACI Building Code permits a moment magnifier approach for design of slender reinforced concrete (RC) columns. This approach is strongly influenced by the effective flexural stiffness EI of the columns, which varies due to cracking, creep, and nonlinearity of the concrete stress-strain curve, among other factors. However, the EI expressions given in the ACI Building Code are quite approximate when compared with the values of EI derived from thrust-moment-curvature relationships. This study was undertaken to determine the influence of a full range of variables on EI of slender tied rectangular RC columns bent in symmetrical single curvature under short-time loads. Approximately 9500 columns, each with a different combination of variables, were used to generate the stiffness data. The EI expressions were then statistically developed for use in slender column designs. Two sets of equations are proposed in this paper: (a) Eq. (21) through (23) for initial sizing and preliminary design of structures; and (b) Eq. (18) through (20) for use in final (more accurate) structural designs.