Bending Failure of an Under-Reinforced Concrete Beam.


    Reinforced concrete
    1,000 x 50 x 100mm deep
    Designed for ductile failure

This video shows how a reinforced concrete beam fails when the correct amount of longitudinal (or flexural) reinforcement is provided.

Longitudinal steel bars are provided to resist the tensile forces in the bottom of the beam due to bending (or flexure).

As demonstrated in the testing videos, concrete is strong in compression, relatively weak in tension, and brittle.

By comparison, steel is strong in both tension and compression; and ductile.

These properties are made use-of in the design of the beam to ensure that, when it fails, the failure mechanism is gradual and controlled. Not sudden and catastrophic!

Note how a near-vertical crack starts to form under the applied load on the right-hand side of the beam as the flexural steel reinforcement starts to yield. Note also how this happens before the concrete at the top of the beam starts to fail in compression.

The graph shows how significant deflection of the beam occurs, causing cracks to form, well before the ultimate failure load is reached.

Learning outcomes

This video will help students answer questions such as:

  • What is reinforced concrete?
  • How does a simply-supported, reinforced concrete beam deflect under a downwards load?
  • Where does the reinforcement need to be positioned in a simply-supported beam to resist tension forces due to bending?
  • How are the ductile properties of steel made use-of in reinforced concrete design?



Bending Failure of an Under-Reinforced Concrete Beam by Think Up is licensed under a Creative Commons Attribution 3.0 Unported License.
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