Flexural Rigidity of Concrete Column Sections

The examination of theoretical stiffness ratios for reinforced concrete sections under uniaxial bending and axial load has shown that a reasonably simple set of approximate equations can be derived to enable a safe estimate of such stiffnesses to be computed. Due to the quantity of computing involved, the theoretical computations were limited to combinations of concrete strength and steel proportion within the practical ranges of 3,000 psi to 5,000 psi and 0.01 to 0.03 respectively, and to three proportions of cross-section geometry. It is customary to use either the uncracked or fully cracked stiffness in analysis. The method presented has the advantage of a more accurate estimate of stiffness in the middle range, though strain history effects should be incorporated, as wiht other methods.