How to Calculate Column Size for Structural Design: Rectangular, Square, and Circular Columns -lceted LCETED INSTITUTE FOR CIVIL ENGINEERS

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Apr 6, 2024

How to Calculate Column Size for Structural Design: Rectangular, Square, and Circular Columns

Title: How to Calculate Column Size for Structural Design

Introduction: Columns play a pivotal role in the structural integrity of buildings, supporting loads from floors, beams, and roofs. Determining their size involves meticulous calculation, considering factors such as total load, material strength, and design specifications. Here's a comprehensive guide to help you accurately calculate the size of columns for your structural design projects.

How to Calculate Column Size for Structural Design

1. Basic Guide:

Step 1: Determine Design Requirements

  • Begin by identifying the total load the column will bear, crucial for ensuring structural stability.
  • Select the appropriate material for the column, whether concrete, steel, or a composite material.
  • Familiarize yourself with building codes and regulations governing column dimensions and materials to adhere to safety standards.

Step 2: Calculate Loads

  • Calculate the total axial load (Pu) that the column will endure, considering all potential loads such as live loads, wind forces, and seismic loads.

Step 3: Select Material Properties

  • Determine the characteristic compressive strength of concrete (fck) and the yield strength of steel (fy) based on material specifications and industry standards.

Step 4: Design the Column

  • Utilize structural engineering principles to design the column, ensuring it can safely withstand the calculated loads.
  • Choose the shape of the column—whether square, rectangular, or circular—based on design requirements and aesthetic preferences.

2. Calculation Example:

Given Data:

  • Total axial load (Pu) = 2500 kN
  • Characteristic compressive strength of concrete (fck) = 30 N/mm²
  • Yield strength of steel (fy) = 415 N/mm²
  • Percentage of steel reinforcement (Asc) = 1.5% of Ac

Calculation Steps:

Step 1: Determine Factored Load

  • Factor in safety considerations by multiplying the total load by a safety factor, typically 1.5, to obtain the factored load (Pu).

Calculate Column Size for Structural Design

Step 2: Calculate Concrete Area (Ac)

  • Utilize the Pu = 0.4 x fck x Ac + 0.67 x fy x Asc formula to determine the sectional area of concrete (Ac).

Step 3: Calculate Column Dimensions

  • For Square Columns: Calculate the side length (L) using the equation Ac = L².
  • For Rectangular Columns: Calculate the length (L) based on a chosen width.
  • For Circular Columns: Calculate the diameter using the cross-sectional area formula for a circle.

Example Calculations: (Insert example calculations as per previous version.)

Given Data:

Total load over the column = 2500 kN

Factored load (Pu) = 1.5 x Total load = 1.5 x 2500 kN = 3750 kN = 3750 x 10³N (the factored load (Pu) is the ultimate load considered for the column, with a safety factor of 1.5 applied to the total load.)

Characteristic compressive strength of concrete (fck) = 30 N/mm² (fck represents the maximum stress concrete can withstand under compression, determined by testing samples.)

Yield strength of steel (fy) = 415 N/mm² (fy is the stress at which steel begins to deform plastically, indicating its maximum load-bearing capacity without permanent deformation.)

Percentage of steel reinforcement (Asc) = 1.5% of Ac =0.015 Ac (Asc represents the area of steel reinforcement within the concrete column, typically a percentage of the total concrete area.)


Calculate Sectional Area of Concrete (Ac):

Using the equation Pu=0.4×fck×Ac+0.67×fy×Asc,

we can solve for Ac.


  • Pu = 3750 x 10³N
  • fck = 30 N/mm²
  • fy = 415 N/mm²
  • Asc = 1.5% of Ac

Let's denote Asc as 0.015Ac.


3750 x 103 = 12Ac + 4.1715Ac

3750 x 103= 16.1715Ac

Ac = (3750 x 103​ )/16.1715

Ac = 231,619.63 mm2

Calculate Square Column Size:

Since Ac=L2, we can solve for L.


L = √231,619.63​

L = 481.38 mm

Thus, the size of the square column will be approximately 481.38 mm x 481.38 mm.

Calculate Rectangular Column Size:

Let's assume a chosen width (B) of 300 mm for the rectangular column.


231,619.63 = L×300

L = 231,619.63​/300

L = 772.07 mm

Thus, the size of the rectangular column will be approximately 300 mm x 772.07 mm.

Calculate Circular Column Diameter:

Using the cross-sectional area formula A = (π×Diameter2)/4​, we can solve for the diameter (D).

231,619.63 = (π×Diameter2)/4​

926,478.52 = π x Diameter2

Diameter2 = 926,478.52​/ π

Diameter = √926,478.52​​ / π

Diameter = 542.09 mm

Thus, the diameter of the circular column will be approximately 542.09 mm.

3. Practical Considerations:

When designing columns for different types of buildings, practical considerations come into play:

  • Residential Buildings: In residential construction, columns are often sized to match the width of the walls, typically around 225 mm (9 inches). This alignment ensures structural uniformity and aesthetic coherence within the space.


  • Commercial Buildings: For commercial structures, larger column sizes may be necessary to accommodate heavier loads and provide enhanced structural support. A minimum column size of 300 mm x 300 mm (12 inches x 12 inches) is commonly employed in commercial construction to meet these requirements.


  • School Buildings: In educational facilities, where safety is paramount, columns are designed to withstand various loads while maintaining a visually pleasing aesthetic. A minimum column size of 350 mm x 350 mm (14 inches x 14 inches) is often specified to ensure adequate support and stability in school buildings.


Conclusion: By following this comprehensive guide and considering practical dimensions for different building types, you can accurately calculate the size of columns for your structural design projects. Remember to prioritize safety, adhere to building codes, and consult with structural engineers when necessary to ensure the structural integrity of your designs.


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