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
Shading for housing, a design guide
A look back at embedding a new culture of shading.
The Architectural Technology Awards
The AT Awards 2025 are open for entries!
ECA Blueprint for Electrification
The 'mosaic of interconnected challenges' and how to deliver the UK’s Transition to Clean Power.
Grenfell Tower Principal Contractor Award notice
Tower repair and maintenance contractor announced as demolition contractor.
Passivhaus social homes benefit from heat pump service
Sixteen new homes designed and built to achieve Passivhaus constructed in Dumfries & Galloway.
CABE Publishes Results of 2025 Building Control Survey
Concern over lack of understanding of how roles have changed since the introduction of the BSA 2022.
British Architectural Sculpture 1851-1951
A rich heritage of decorative and figurative sculpture. Book review.
A programme to tackle the lack of diversity.
Independent Building Control review panel
Five members of the newly established, Grenfell Tower Inquiry recommended, panel appointed.
Welsh Recharging Electrical Skills Charter progresses
ECA progressing on the ‘asks’ of the Recharging Electrical Skills Charter at the Senedd in Wales.
A brief history from 1890s to 2020s.
CIOB and CORBON combine forces
To elevate professional standards in Nigeria’s construction industry.
Amendment to the GB Energy Bill welcomed by ECA
Move prevents nationally-owned energy company from investing in solar panels produced by modern slavery.
Gregor Harvie argues that AI is state-sanctioned theft of IP.
Experimental AI housing target help for councils
Experimental AI could help councils meet housing targets by digitising records.
BSRIA Occupant Wellbeing survey BOW
Occupant satisfaction and wellbeing tool inc. physical environment, indoor facilities, functionality and accessibility.