Slenderness ratio (λ)
λ = effective length/least lateral dimension
If λ > 12 then the column is long.
Load carrying capacity for short column
P = σ_{sc}A_{sc} + σ_{cc}A_{c}
where, AC = Area of concrete, A_{c} = A_{g}  A_{SC}
σ_{SC} Stress in compression steel
σ_{CC} Stress in concrete
A_{g} Total gross crosssectional area
A_{SC} Area of compression steel
Load carrying capacity for long column
P = C_{r}(σ_{sc}A_{sc} + σ_{cc}A_{c})
where, Cr = Reduction factor
where, l_{eff} = Effective length of the column
B = Least lateral dimension
i_{min} = Least radius of gyration and
where, l = Moment of inertia and A = Crosssectional area
Effective length of Compression Members
Column with helical reinforcement
Strength of the column is increased by 5%
P = 1.05(σ_{sc}A_{sc} + σ_{cc}A_{c}) for short column
P = 1.05C_{r}(σ_{sc}A_{sc} + σ_{cc}A_{c}) for long column
Longitudinal reinforcement
Minimum number of bars for reinforcement
For rectangular column 4
For circular column 6
Minimum diameter of bar = 12 mm
Maximum distance between longitudinal bar = 300 mm
Pedestal: It is a short length whose effective length is not more than 3 times of lest lateral dimension.
Transverse reinforcement (Ties)
where ϕ_{min} dia of the main longitudinal bar
φ = dia of the bar for transverse reinforcement
Pitch (p)
where, φ_{min} = minimum dia of main longitudinal bar
Helical reinforcement
Some others IS recommendations
λ<12 Short column
Concentrically Loaded Columns
Where e = 0, i.e., the column is truly axially loaded.
P_{u} = 0.45 f_{ck}A_{c} + 0.75 f_{y}A_{sc}
This formula is also used for member subjected to combined axial load and biaxial bending and also used when e > 0.05 D.
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1. What are the different types of columns used in civil engineering? 
2. How do you design a reinforced concrete column? 
3. What is the importance of column design in structural engineering? 
4. How do you calculate the load capacity of a column? 
5. What are the common failure modes in column design? 

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