Direct Design of Rectangular Columns with Bending About an Axis of Symmetry
Henry J. Cowan
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A new method for the design of eccentrically loaded reinforced concrete columns based on the principle of superposition. The section is designed to resist the bending moment due to the eccen-tricity of the column load, using the well-known equations for rectangular reinforced concrete beams; the area of reinforcement is then reduced to allow for the direct compression due to the column load. In the standard method the dimensions of the section are assumed and the depth of the neutral axis and the maximum stresses in the steel and the concrete are then calculated. In the present method the neutral axis depth ratio is assumed, and thedimensions of the section are calculated from the maximum permissible stresses of the materials; this is therefore a direct design procedure. Rules are given for determining the depths of the neutral axis so as to produce a section with (a) a specified percentage of tension reinforcement only; (b) a specified percentage of symmetrical reinforcement; (c) the lowest possible area of (unsymmetrical) reinforcement within the limits set by the dimensions of the cross section; and (d) the lowest possible area of reinforcement when the dimensions of the cross section are not limited.