A material will initially
deform elastically, but once it has surpassed its yield strength, it will
deform plastically. For materials such as steel, which give a ductile failure
response, the compressive and tensile yield strength are roughly equal.
Concrete however will fail
at very low tensile stresses, the compressive strength far exceeds the tensile
The reasons for concrete’s considerable
compressive strength compared to its tensile strength are:
- When in compression,
the aggregate and the paste both resist the stresses in the concrete. Stresses
of 20-60+MPa can be withstood.
- When in tension, only
the cement paste resists the stresses. It will fail at stresses of 2-5MPa.
When designing for the
ultimate limit state, the element is considered to fail at its yield stress.
Hence, yield strengths often carry large safety factors in design.
A material visibly breaks at the ultimate tensile strength.