When constructing any building, understanding load bearing column calculation is one of the most important tasks for structural stability. A column is the main vertical structural member that carries the load of beams, slabs, and walls above it, transferring these loads safely down to the foundation. If the column design or calculation is not accurate, it can compromise the safety and durability of the entire structure. This guide explains everything about load bearing column calculation in simple terms so that engineers, students, and homeowners can understand it clearly.
What is a Load Bearing Column?
A load bearing column is a vertical structural element that transfers the total load from the slab, beam, and other structural members to the footing below. These columns are designed to resist compression, bending, shear, and sometimes torsional forces. In simple words, the column acts like the backbone of a building. Without properly calculated columns, the structure cannot stand safely.
Importance of Load Bearing Column Calculation
Accurate load bearing column calculation is essential for both safety and cost efficiency. If a column is under-designed, it may fail and cause structural collapse. If it is over-designed, it may lead to wastage of concrete and steel, increasing the overall cost. Therefore, calculations must strike the right balance.
Key Factors in Load Bearing Column Design
Before calculating the column size and reinforcement, engineers consider certain factors. These include type of structure, number of floors, soil condition, live load, and material strength.
1. Type of Load
Columns must be designed to resist both axial loads (vertical loads) and lateral loads (such as wind or earthquake forces). Understanding the type of load is the first step in column design.
2. Number of Storeys
The more storeys a building has, the greater the load on lower columns. For example, a column in a two-storey building will carry far less load compared to a column in a ten-storey building.
3. Soil Bearing Capacity
The type of soil plays an important role. Weak soil requires larger footing and bigger columns, while strong soil allows smaller column dimensions.
4. Material Strength
Concrete grade (M20, M25, M30, etc.) and steel grade (Fe415, Fe500, etc.) directly impact the load carrying capacity of the column. Higher grades mean more strength but also more cost.
5. Safety Factors
Engineers always include a factor of safety in their calculation to cover unforeseen circumstances like material defects, unexpected loads, or minor design errors.
Step-by-Step Load Bearing Column Calculation
Now let us understand how to calculate load bearing columns in a simple step-by-step method.
Step 1: Calculate Dead Load
Dead load includes the self-weight of structural components such as slab, beams, walls, and columns. For example:
- RCC slab: 3 to 4 kN/m²
- Beams: 2 to 3 kN/m²
- Brick wall: 10 to 12 kN/m
Step 2: Calculate Live Load
Live load depends on building usage. For residential houses, it is usually 2 to 3 kN/m². For commercial or industrial buildings, live load can be much higher.
Step 3: Total Load on Column
Total load = Dead Load + Live Load + Floor Finish + Service Load (electrical, plumbing, etc.). Multiply this load by the influence area each column supports.
Step 4: Load Distribution
Divide the total building load by the number of columns to get approximate load per column. This gives a starting point for further design.
Step 5: Column Axial Load
Axial load = (Total Load × Load Distribution Factor) + Factor of Safety. This ensures columns are safe even under unexpected conditions.
Step 6: Column Size Calculation
General thumb rule:
- For G+1 building: Minimum column size is 9” × 9” with M20 concrete.
- For G+2 building: Minimum 12” × 9”.
- For higher floors: Larger dimensions are required depending on load.
Step 7: Reinforcement Calculation
Columns are reinforced with vertical bars and ties. Common practice:
- Minimum 4 bars of 12 mm diameter.
- For larger loads, 6–8 bars of 16 mm to 20 mm diameter.
- Ties of 8 mm diameter spaced at 150 mm–300 mm center-to-center.
Example of Load Bearing Column Calculation
Suppose a two-storey residential building has a slab load of 4 kN/m², live load of 3 kN/m², and wall load of 10 kN/m. For a 4m × 4m room, the total load on one column can be calculated and reinforcement designed accordingly. This ensures proper safety.
Common Mistakes in Column Calculation
Even skilled workers sometimes make mistakes. The most common errors include:
- Ignoring soil conditions.
- Using undersized columns to save material.
- Placing reinforcement without proper cover.
- Not considering earthquake or wind load.
- Using low-grade concrete or steel.
FAQs on Load Bearing Column Calculation
What is the minimum column size for a 2-storey house?
The minimum size is 9” × 9” with M20 grade concrete, but 12” × 9” is recommended for extra safety.
How many columns are needed for a 2-storey house?
It depends on the plan, but generally columns are placed at 3m–4m spacing for stability.
Can we build a house without columns?
Yes, in load bearing wall construction, columns are not used. But in modern RCC buildings, columns are essential for durability and safety.
How to calculate steel in a column?
Steel percentage in columns is usually 0.8% to 6% of gross cross-sectional area, depending on load.
Which software is used for column design?
STAAD Pro, ETABS, AutoCAD, and SAP2000 are popular for professional structural design.
Conclusion
Load bearing column calculation is not just about numbers, but about safety, cost efficiency, and long-term durability. By following correct design principles, considering soil strength, using the right concrete and steel, and avoiding common mistakes, engineers ensure strong and stable buildings. Whether you are a civil engineering student, contractor, or homeowner, understanding the basics of load bearing column calculation helps in making better construction decisions.
