 The strength of short columns is controlled by the strength of the material and the geometry of the cross section.Reinforcing rebar is placed axially in the column to provide additional axial stiffness.Accounting for the additional stiffness of the steel, the nominal loading capacity Pn for the column in terms of the maximum compressive stress of the concrete fc', the yield stress of the steel fy, the gross cross section area of the column Ag, and the total cross section area of the steel rebar Ast
where the first term represents the load carried by the concrete and the second term represents the load carried by the steel.