Cost Optimization of Column

The cost differences between circular and square column increase with the increase in gross area of concrete. The ratio of longitudinal steel area to gross concrete section is in the range from 0.01 to 0.08, according to BNBC/ACI Code. The common practice is to choose an arbitrary section and check that for bending and axial load with a reinforcement ratio around 2-3 % but we don�t know whether it is economical or not. However, for a particular moment and load there is only one section which is economical, it means only for a certain percentage of reinforcement the section will be optimized. Since the cost of concrete and reinforcement are different which may increase or decrease independently, the percentage of reinforcement in the optimized section varies with the price ratio of steel to concrete. Analysing for the present cost ratio of steel and concrete, it is seen that a column section is optimized at 1 percent of reinforcement for low-rise to medium rise building. This is true for any column that after a certain price ratio it is optimized at reinforcement of the order of 1 percent on that loading and moment condition. Use of high strength concrete in the column has an effect of minimizing the cost. Using 5000 psi concrete instead of 3000 psi concrete saves 20-50 percent of total cost in general. For same axial load and moment resisting capacity, a circular column is found to be more costly than a square column. Also, the cost differences between circular and square column increase with the increase in gross area of concrete.