Point of contraflexure
|
| The point of contraflexure (PoC) occurs where bending is zero and at the point of change between positive and negative (or between compression and tension). |
In a beam that is flexing (or bending), the point where there is zero bending moment is called the point of contraflexure. At that point, the direction of bending changes its sign from positive to negative or from negative to positive. (It may also be thought of as a change from compression to tension or vice versa).
For this change to happen, it must pass through zero – the point of contraflexure. On a bending moment diagram, it is the point at which the bending moment curve intersects with the zero line.
An analogy may be made with a speeding train travelling west on a single track. In order to reverse direction and travel east, it must decelerate, stop then accelerate in the opposite direction. The point it stops, even if momentary, is zero – the neutral point, where it is not travelling.
Theoretically, when considering a structural member under load, such as a reinforced concrete beam, the point of zero bending moment would seem to suggest no reinforcement would be required. However, omitting reinforcement at that point is considered inadvisable as, in a real-life situation, it may be difficult to locate the exact point of contraflexure.
[edit] Related articles on Designing Buildings Wiki
Featured articles and news
Great British Energy install solar on school and NHS sites
200 schools and 200 NHS sites to get solar systems, as first project of the newly formed government initiative.
600 million for 60,000 more skilled construction workers
Announced by Treasury ahead of the Spring Statement.
The restoration of the novelist’s birthplace in Eastwood.
Life Critical Fire Safety External Wall System LCFS EWS
Breaking down what is meant by this now often used term.
PAC report on the Remediation of Dangerous Cladding
Recommendations on workforce, transparency, support, insurance, funding, fraud and mismanagement.
New towns, expanded settlements and housing delivery
Modular inquiry asks if new towns and expanded settlements are an effective means of delivering housing.
Building Engineering Business Survey Q1 2025
Survey shows growth remains flat as skill shortages and volatile pricing persist.
Construction contract awards remain buoyant
Infrastructure up but residential struggles.
Home builders call for suspension of Building Safety Levy
HBF with over 100 home builders write to the Chancellor.
CIOB Apprentice of the Year 2024/2025
CIOB names James Monk a quantity surveyor from Cambridge as the winner.
Warm Homes Plan and existing energy bill support policies
Breaking down what existing policies are and what they do.
Treasury responds to sector submission on Warm Homes
Trade associations call on Government to make good on manifesto pledge for the upgrading of 5 million homes.
A tour through Robotic Installation Systems for Elevators, Innovation Labs, MetaCore and PORT tech.
A dynamic brand built for impact stitched into BSRIA’s building fabric.
BS 9991:2024 and the recently published CLC advisory note
Fire safety in the design, management and use of residential buildings. Code of practice.