Materials & Civil
Intermediate

Factor of Safety

Ratio of a material strength to the actual applied stress.

Formula

FoS=σultσallowFoS = \frac{\sigma_{ult}}{\sigma_{allow}}

Variables

\sigma_{ult}Ultimate strength
\sigma_{allow}Working stress

Example

FoS of 2 means twice the needed strength

Did You Know?

Buildings typically use a factor of safety of 2 to 5.

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