What is elastic deformation?
Elastic deformation is the temporary change in shape or size of a structural element under load that fully reverses once the load is removed. It is the opposite of plastic deformation, where part of the shape change is permanent.
How does elastic deformation arise?
Under load, molecules or atoms shift slightly relative to each other. In elastic behaviour:
- only reversible deformations occur
- there is a linear relationship between force and deformation (Hooke’s law)
- energy is temporarily stored in the material
- no damage occurs at the micro scale
Once the load is removed, the molecules release the stored energy and the element returns to its original shape.
Types of elastic deformation
| Type | Example |
|---|---|
| Extension | A hanger rod in tension |
| Compression | A column under axial load |
| Bending (deflection) | A floor beam under live load |
| Torsion | A drive shaft under twisting |
| Shear | A steel plate under shear force |
Importance in construction
A structure must only deform elastically under service load, otherwise permanent damage occurs. Engineers therefore calculate:
- Serviceability Limit State (SLS) — deformations that become noticeable (e.g. deflection < L/250)
- Ultimate Limit State (ULS) — to prevent plastic deformation or collapse
- Spring stiffness of foundations — settlement partly elastic, partly permanent
- Vibration behaviour — natural frequency of floors and bridges
Practical examples
- Steel beam: bends under load and springs back without damage
- Car crossing a bridge: the deck moves a few millimetres
- Wind on a high-rise: the top can sway tens of centimetres
- Prestressed concrete beam: controlled elastic deformation through tendon force
Related terms
- Elasticity
- Modulus of elasticity
- Plastic deformation
- Plasticity
- Loading
- Serviceability
Looking for more DIY plans? Check out fredsdiyplans.com.