The minimum reinforcement in concrete members is specified in various national codes is to prevent cracking due to thermal shrinkage and creep in concrete as concrete is very weak in tension and also to prevent water ingress in to the concrete element through the cracks causing weathering of concrete and corrosion of reinforcement which affects durability in short term and long run.
The below are the various code requirements pertaining to the minimum reinforcement steel requirements.
Indian code IS 456 : 2000
The column is defined to be a member carrying direct axial and the effective length of which is more than three times the least lateral dimension.
According to clause 26.5.3.1, The cross sectional area of longitudinal reinforcement shall not be less than 0.8 percent of cross sectional area of concrete (the area required to resist the direct stress not upon actual area).
In addition to the above requirement Indian code also specifies the minimum number of bars of 4 in rectangular/square column and 6 in circular column with bar diameter not being less than 12mm in same clause (26.5.3.1.e).
For Pedestals (whose effective length is less than three times the least lateral dimension) the minimum reinforcement is specified as 0.15 percent cross sectional area of concrete.
British Code BS 8110 Part 1 : 1997
The British code does not specify any difference between pedestal and column and specifies a minimum cross sectional area of reinforcement steel according to clause 3.12.5.3 and Table 3.25 to 0.4 percentage of concrete cross sectional area for both column and pedestal.
In same clause the minimum number and size of bar is specified as “The minimum number of longitudinal bars in a column should be four in rectangular columns and six in circular columns, and the size of bar should be not less than 12 mm”.
American Code ACI 318–11
According to clause 10.9.1 the minimum reinforcement in non composite compression members is specified as one percent of gross cross sectional area of compression member.
In addition to the above requirement, the code also specifies in clause 10.9.2 the minimum number of bars being 4 numbers enclosed inside the rectangular/square/circular ties and 6 numbers for bars enclosed inside spirals conforming to clause 10.9.3 (spiral ties requirements)
However, the ACI 318 is silent on the minimum diameter of bar.
Eurocode 2 (EC1992)
The Eurocode 2 recommends a minimum reinforcement bar diameter to 8mm as per clause 9.5.2 (1) and as per Clause 9.5.2 (2),
Minimum reinforcement of
As,min = 0.10NEd/fyd or 0.002Ac, whichever is greater
where, As,min = Minimum Longitudinal reinforcement in column
NEd = Design Axial Compression Force,
fyd = Design Yield strength of reinforcement,
Ac = Cross sectional area of concrete
Eurocode also has National Annexes to it as per the countries and the above values specified to be considered as per the respective National Annexure.
Singapore Code SSCP 65 Part 1 : 1999
The minimum reinforcement requirements to the columns as per the Singapore Standard are similar to that of British Code and the values are specified in Clause 3.12.5.3 and Table 3.27 of SSCP 65 Part 1 : 1999.