Column Reinforcement According to IS Code, BS Code and ACI Codes | Minimum and Maximum Reinforcement in Columns

Column is a structural member that transfer load from slab and beams to the ground through foundation. Thus column is one of the most important structural member of the building.

Column faces tensile and compressive forces acting on it. As we know concrete is very good in compression and steel is better in tackling tensile stresses. Thus concrete and steel reinforcement in column is important.

Column can take load acting on the structure because of reinforcement in the column. Thus steel reinforcement in concrete should be properly considered.

Minimum and Maximum Column Reinforcement Details

Some basic requirements for a structural column should be kept in mind before designing column reinforcement.

Minimum Column Reinforcement

Certain minimum reinforcement should be used in column to avoid sudden failure of the building or structural member. Minimum reinforcement in concrete member permits concrete members to show adequate signs of failure.

Minimum tensile strength of concrete is required to avoid sudden failure of the concrete member.

Minimum Column Reinforcement According to British standard (BS 8110)

Reinforcement in column should be in no case minimum than 0.4% of the cross-sectional area of concrete section.

Area of steel in column = 0.4% of Gross area of the section

100As/Ac = 0.4

Thus according to BS 8110 minimum reinforcement in column is 0.4% of sectional area of concrete.

Minimum Column Reinforcement According to American Concrete Institute (ACI 318 – 19)

Reinforcement in column should be in no case minimum than 1% of the cross sectional area of concrete section.

Area of steel in column = 1% of Gross area of the section

100As/Ac = 1

Thus according to ACI 318 – 19 minimum reinforcement in column is 1% of sectional area of concrete.

Minimum Column Reinforcement According to Indian Standards (IS: 456 – 2000)

Reinforcement in column should be in no case minimum then 0.8% of the cross sectional area of concrete section.

Area of steel in column = 0.8% of Gross area of the section

100As/Ac = 0.8%

Thus according to IS 456 minimum reinforcement in column is 0.8% of sectional area of concrete.

Maximum column Reinforcement

Certain maximum reinforcement should be used in column so as to avoid over-reinforcement. Maximum reinforcement in column is the upper limit of steel that can be used in column.

Maximum Column Reinforcement According to British standard (BS 8110)

Reinforcement in column should be in no case greater then the area of steel shown below:

• Vertically cast column – 6%
• Horizontally cast column – 8%
• Lapps in vertically/horizontally cast column – 10%

Thus according to BS 8110 maximum reinforcement in column is 6% of sectional area of concrete.

Maximum Column Reinforcement According to American Concrete Institute (ACI 318 – 19)

Reinforcement in column should be in no case greater then 8% of the cross sectional area of concrete section.

Area of steel in column should be less then or equal to 8% of Gross area of the section

Thus according to ACI 318 – 19 maximum reinforcement in column is 8% of sectional area of concrete.

Maximum Column Reinforcement According to Indian Standards (IS: 456 – 2000)

Reinforcement in column should be in no case maximum then 6% of the cross sectional area of concrete section.

Area of steel in column should be less then or equal to 6% of Gross area of the section

Thus according to IS 456 minimum reinforcement in column is 6% of sectional area of concrete.

Minimum and Maximum Column Steel Requirement

Steel or reinforcement requirement in column as per different standards like Indian Standards, British Standard and American Concrete Institute are shown below.

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Minimum Reinforcement According to Type of Column

Column Reinforcement changes according to type of column and shape of column. Minimum dia of bars and number of bars required in a column are shown below.

Thus in case of square or rectangle column minimum 4 number of bars should be used. Nut in case of circular column minimum 6 number of bars should be used. Minimum dia of bar used in column shall not be less then 12 mm dia.

Column Reinforcement Details

Reinforcement details in columns are given below. Guidelines for designing column are listed below.

Longitudinal Steel

• Maximum reinforcement in any column shall not exceed 6% of the gross area of concrete.
• Minimum reinforcement should not be less then 0.8% of the gross sectional area of concrete.
• Minimum size of primary reinforcement should not be less then 12mm.
• Maximum size of reinforcement in column should not be more then 50mm.
• For rectangular structure minimum 4 number of bars should be used.
• For circular column section 6 number of bars should be used.
• For workable concrete minimum cover of 40mm or diameter of bar whichever is greater should be provided.
• Effective length should be 48 times the diameter of bar.

Transverse Reinforcement

• Minimum spacing between two bars shall not be less then the diameter of greater bar or 5mm more then the nominal maximum size of coarse aggregate.
• Minimum size of lateral ties should not be less then 1/4 of the diameter of the largest longitudinal bar but not less then 5mm.
• The maximum diameter of the ties or helical steel should preferably be not more than 12 mm and 25 mm respectively.
• If helical ties are used then the spacing between the longitudinal reinforcement should not be more then 300mm.
• The maximum pitch for helical reinforcement should not be more then 75mm and minimum pitch should not be less then 25mm.

Frequently Asked Question