Understanding Tension and Compression in Structures

In any structure or building, two fundamental forces come into play: tension and compression. These forces act on materials, and each material has its unique capacity to handle them.

Materials and Their Abilities

• Some materials excel at withstanding compression.
• Others handle tension more effectively.
• Certain materials can handle both tension and compression.

Tension: Pulling Things Apart

When a force pulls a material apart, it’s known as tension. This force tries to stretch the material. For instance, when an object is hung from a rope, gravity pulls on it, attempting to elongate the cord.

• Tension force formula: T = mg + ma
• Tension force unit: Newtons (N)
• Tensile stress: Force per unit area
• Tensile strain: Increase in length compared to the original length

Compression: Squeezing Things Together

Compression is the force that squeezes or shortens materials together. When we push down on a spring, we apply a compression force. This force can act in one direction (uniaxial) or multiple directions (biaxial or triaxial).

• Compression force formula: N = ma
• Compression force unit: Newtons (N)
• Compressive stress: Force per unit section
• Compressive strain: Reduction in length compared to the original length

Bending Stress

Materials experience both tension and compression when they bend. For example, in a beam, the bottom part undergoes tension while the top part experiences compression. The neutral axis in the middle of the beam experiences no stresses during bending.

Designing for Forces

Both tension and compression forces are critical considerations in structural design. If a material can’t handle these forces, a structure may collapse under dead and live loads. Therefore, all structures must be designed to withstand these forces.

Managing Forces

• Transferring force involves moving it from a vulnerable area to a stronger one.
• Dissipating force spreads it out over a larger area, reducing concentrated impacts.

Examples in Bridges

• Dissipation: Arch Bridge
• Transfer: Suspension Bridge

Difference Between Tension and Compression: A Comparison

Aspect	Tension	Compression
Definition	Pulling material apart	Squeezing material together
Effect on Material	Tries to stretch material	Tries to shorten material
Representation	T = mg + ma	N = ma
Units	Newtons (N)	Newtons (N)
Stress	Tensile Stress	Compressive Stress
Strain	Ratio of increase in length to original length	Ratio of reduction in length to original length
Example	Pulling a rope	Compressing a spring
Application	Bridges, ropes, cables, etc.	Columns, pillars, beams, etc.
Critical Failure	Buckling due to excessive compression force	Snapping due to excessive tension force
Management	Transfer or dissipate force	Transfer or dissipate force