a 70 ft high reinforced concrete column with a cross section of 12 by 24 in. and reinforcement ratio as/ac (x-sectional area of steel to x-sectional area of concrete) of 0.02 and grade 60 steel (this steel grade has a yield strength of 60,000 psi) is designed to resist load in compression. the initial stress level in the concrete is 1500 psi. the 28-day compressive strength (fc’) is 4,500 psi.