Minimum (Nominal) Area of Reinforcement in Column

I would like to share some engineering related problems as I encounter different kind of cases from the pasts so that I have somewhere to refer back to. Eurocodes / British Standards / text books are just a lot of pages to look up.

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.

In my case, I was designing a concrete column stump for a footing.

Say I am designing a non-structural WxLxh: 1800mm x 500mm x 1000mm

This calculation can also apply for structural stump (which will carry / transfer axial loads).

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”.

Example: For a 1800mm x 500mm x 1000mm column stump,

As,min = (0.4/100)x(1800mm x 500mm) = 3600m^2

Therefor I'll take around 30 nos of H13 rebar. H16 would be too excessive for a non structural design.


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 Annex.

Example: For a 1800mm x 500mm x 1000mm column stump,

This is a non structural design as the loads are too small, I don't consider axial loads. Assuming this is a structural purpose,

I'll take the axial loads (NEd) from whatever on top of the column, say NEd = 10kN

For a steel yield strength, fyk = 500Mpa,

As,min = 0.1(10e3)/(0.87 x fyk) = 0.1(10e3)/(0.87x500)
As, min = 2.29 N/mm^2

The As,min from EC is too small so I'll take nominal area from BS.


Sources: 1 2