Guide to Design of RCC Columns
Reinforced Concrete Columns
A column is defined as a compression member, the effective length of which exceeds three times the least lateral dimension. Compression members whose lengths do not exceed three times the least lateral dimension, may be made of plain concrete.
Please see the link for formulas to calculate axial loads in columns. I would recommend using advanced structural design software like ETabs or Staad Pro for design of structures. Column design does not depend only on axial loads, but also on many other factors. There are bending moments and tortional forces induced due to beam spans, wind loads, seismic loads, point loads and many other factors.
A column may be classified based on different criteria such as:
1. Based on shape
- Rectangle
- Square
- Circular
- Polygon
2. Based on slenderness ratio
- Short RCC column, =< 10
- Long RCC column, > 10
- Short Steel column, =<50
- Intermediate Steel column >50 & <200
- Long Steel column >200
3. Based on type of loading
- Axially loaded column
- A column subjected to axial load and unaxial bending
- A column subjected to axial load and biaxial bending
4. Based on pattern of lateral reinforcement
- Tied RCC columns
- Spiral RCC columns
Minimum eccentricity
Types of Reinforcements for columns and their requirements
Longitudinal Reinforcement
- Minimum area of cross-section of longitudinal bars must be atleast 0.8% of gross section area of the column.
- Maximum area of cross-section of longitudinal bars must not exceed 6% of the gross cross-section area of the column.
- The bars should not be less than 12mm in diameter.
- Minimum number of longitudinal bars must be four in rectangular column and 6 in circular column.
- Spacing of longitudinal bars measures along the periphery of a column should not exceed 300mm.
Transverse reinforcement
- It maybe in the form of lateral ties or spirals.
- The diameter of the lateral ties should not be less than 1/4th of the diameter of the largest longitudinal bar and in no case less than 6mm.
- Least lateral dimension
- 16 x diameter of longitudinal bars (small)
- 300mm
Helical Reinforcement
- 75mm
- 1/6th of the core diameter of the column
- 25mm
- 3 x diameter of helical bar
- 16 x diameter of longitudinal bar (smaller)
- 300mm
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