Short Answer:

A column is a vertical compression member in a structure that carries loads mainly along its longitudinal axis. It is designed to support beams or slabs and transfer loads safely to the foundation. Columns are generally long, vertical, and fixed at both ends to resist buckling and crushing.

A strut, on the other hand, is a compression member that may be horizontal, inclined, or vertical, and it is mainly used in frameworks such as trusses to resist compressive forces. Both columns and struts carry compressive loads, but their orientation and applications differ based on design needs.

Detailed Explanation :

Column and Strut

Columns and struts are both compression members, meaning they carry loads that tend to shorten or crush them. They are widely used in mechanical and civil engineering structures like buildings, bridges, towers, and machine frames. The main difference lies in their orientation, application, and type of end supports.

While a column is usually vertical and forms part of a building’s framework, a strut can be positioned in any direction — vertical, horizontal, or inclined — depending on the type of structure. Both play a crucial role in maintaining the stability and strength of structures under compression.

1. Definition of Column

A column is a vertical structural member that transmits compressive loads from beams, slabs, or upper floors to the foundation. It is one of the most important load-bearing elements in a structure.

Columns are designed to resist:

• Axial compression (load acting along the central axis)
• Bending moments (if load acts eccentrically)

The strength and stability of a column depend on its length, cross-sectional shape, material, and end conditions (fixed or hinged).

If the column is too slender, it tends to fail by buckling rather than direct crushing. Therefore, the design of columns must ensure both strength and stability.

2. Definition of Strut

A strut is a compression member of a structure that is not necessarily vertical. It may be horizontal, inclined, or even diagonal, depending on the structure’s configuration. Struts are commonly used in trusses, frameworks, and bridges to resist compressive forces.

The primary function of a strut is to prevent compression or buckling in the framework members. Like columns, struts also fail due to buckling if they are long and slender.

Struts are usually found in:

• Roof trusses
• Bridge trusses
• Machine components (like connecting rods, bicycle frames, aircraft wings)

3. Difference Between Column and Strut

Though both columns and struts carry compressive loads, their differences can be explained as follows:

• Orientation:
  • Column: Always vertical.
  • Strut: May be vertical, horizontal, or inclined.
• Function:
  • Column: Used to support roofs, beams, and floors in buildings.
  • Strut: Used in frameworks to resist compressive forces.
• Load Nature:
  • Column: Carries mainly axial compressive load.
  • Strut: Carries axial compression and may also carry bending loads depending on structure geometry.
• Support Condition:
  • Column: Generally fixed at both ends or sometimes hinged.
  • Strut: May have any type of end conditions depending on design.
• Example:
  • Column: Pillars of buildings or bridges.
  • Strut: Members of a truss bridge or bicycle frame.

4. Classification of Columns and Struts

Both columns and struts can be classified based on their slenderness ratio (L/r), which determines whether the member will fail due to crushing or buckling.

1. Short Column (or Strut):
   • Slenderness ratio < 40
   • Failure occurs due to crushing.
   • Common in concrete or masonry structures.
2. Long Column (or Strut):
   • Slenderness ratio > 80
   • Failure occurs due to buckling.
   • Common in steel or metallic frameworks.
3. Intermediate Column:
   • Slenderness ratio between 40 and 80
   • Failure occurs due to both crushing and buckling combined.

5. Modes of Failure

Columns and struts can fail mainly in two ways:

1. Crushing Failure:
   Occurs in short and thick members where compressive stress exceeds the material’s yield strength.
2. Buckling Failure:
   Occurs in long and slender members. The member bends sideways and fails even before reaching the material’s yield strength. The Euler’s formula is used to calculate the critical buckling load:

where,
= critical load,
= modulus of elasticity,
= least moment of inertia,
= effective length of the member.

The formula shows that buckling depends on the stiffness (EI) and effective length of the member.

6. End Conditions and Their Effects

The effective length of a column or strut varies with end conditions:

• Both ends hinged:
• Both ends fixed:
• One end fixed, other free:
• One end fixed, other hinged:

Shorter effective lengths give higher load-carrying capacity because the member resists buckling better.

7. Applications

Columns:

• Building and bridge supports
• Structural frameworks
• Transmission towers

Struts:

• Roof trusses
• Bridge trusses
• Aircraft frames
• Vehicle suspensions
• Mechanical linkages

In all cases, they ensure structural rigidity, stability, and resistance to compressive stresses.

Conclusion

In conclusion, columns and struts are both compression members that resist loads causing shortening or buckling. A column is primarily a vertical member used in buildings to transfer loads to the foundation, while a strut can be inclined or horizontal and is used in frameworks to resist compressive forces. The performance of both depends on their length, cross-section, material, and end conditions. Proper design of columns and struts ensures safety, stability, and strength of all mechanical and civil engineering structures.