Elastic limit
Contents |
[edit] Introduction
All materials show elastic behaviour to a degree, some more than others. If, after a load has been applied and then quickly removed, a material returns rapidly to its original shape, it is said to be behaving elastically. Elasticity is a crucial characteristic of building materials; if it were not, buildings would suffer continuous deformation under load and ultimately would collapse.
[edit] Elastic limit
A solid material’s elastic limit is the maximum stress per unit area it can withstand before there is permanent deformation. In other words, it is the limit of the material’s elasticity, for up to that point, the solid can resume its original shape when the load is removed; after that point, it undergoes permanent (plastic) deformation and will not return to its original shape even after the load (yield load) has been removed.
On a graph showing a stress-strain curve, the point of the limit of elastic behaviour is called the ‘yield point’ and this is where plastic deformation begins – some of this deformation will be plastic and irreversible. In structural engineering, the yield point is regarded as a ‘soft failure’ mode which does not usually cause catastrophic or ultimate failure. It might be referred to as the fracture point or in the case of structural failure the breaking point, such as where a timber beam goes beyond, the yield, soft failure and fracture to break and collapse.
No structural material exhibits perfect elasticity: depending on the type of structure and the material, permanent deformations are unavoidable whenever loads exceed certain values. That is why engineers design structures to ensure the materials are being used within their elastic range and the loads involved will not produce permanent deformations.
All structural materials behave plastically beyond their elastic range. However, even if some materials show elastic behaviour, they may – after a long period of service, usually many years – exhibit a degree of plastic flow (or creep).
[edit] Linear elasticity
This occurs when the deformation in a material is proportional to the load applied. So, if a person weighing 50kg causes a diving board to deflect by 300mm, and another person weighing 100kg causes an identical board to deflect by 600mm, the diving board is exhibiting linear deflection. Most structural materials are, within limits, linearly elastic and are used within their linearly elastic range.
[edit] Related articles on Designing Buildings
- Concept structural design.
- Detailed design.
- Elements of structure in buildings.
- Moment.
- Stiffness.
- Structural engineer.
- Structural principles.
- Structural systems for offices.
- Structural vibration.
- Structures at the end of their design life.
- The development of structural membranes.
- Types of structural load.
- Vibrations.
Featured articles and news
Celebrating architecture's eloquent champions.
Unusual perspectives on 1960s’ thinking.
AI and the challenges to intellectual property
The legal landscape of adopting AI now and in the future.
Worrying landscape for Welsh construction SMEs revealed.
In recent risk factor analysis report completed by CIOB.
Construction Sport survey highlights risks of dehydration
Supporting construction workers to avoid dangers.
Can your business afford to ignore mental well-being?
£70 - 100 billion annually in UK construction sector.
Mental health in the construction industry
World Mental Health Day 10 October.
Construction awards provide relief in wake of ISG collapse
Spike in major infrastructure awards, housing up but short of targets, are ISG collapse impacts yet to come.
Biodiversity net gain with related updates and terms
Only 0.5% of applications subject to BNG in the context significant proposed changes to planning.
As political power has shifted from blue to red
Has planning now moved from brown to green?
The role of construction in tackling the biodiversity crisis
New CIOB Nature of Building digital series available now.
The Nature Towns and Cities initiative
Grants of up to 1 million for local councils and partners.
The continued ISG fall out October updates
Where to look for answers to frequently asked questions.
Building safety remediation programme for Wales
With 2024 October progress updates.
In major support package for small businesses.
Conservation and transformation
Reading Ruskin’s cultural heritage. Book review.