Flexural Stiffness of Composite Steel Reinforced Concrete Columns

Abstract

The Canadian Standards Association (CSA) Standard A23.3-94 permits a moment magnifier approach for design of slender composite steel-concrete columns. This approach is strongly influenced by the effective flexural stiffness (EI) of the columns. However, the EI expressions given in CSA A23.3-94 are quite approximate when compared with the values of EI derived from axial load-moment-curvature relationships. This study was undertaken to determine the influence of different variables on EI of slender tied rectangular composite columns in which steel sections are encased in concrete. The columns studied were subjected to uniaxial bending in symmetrical single curvature under short-term loads. Approximately 8,000 simulated columns, half of which subjected to bending moment about the major axis and the remaining half subjected to bending moment about the minor axis of the steel section, were used to generate the stiffness data. The EI expressions were then developed for use in slender composite column designs. A design equation is proposed in this paper.