Factor of Safety

Definition

The Factor of Safety quantifies the capacity of a system beyond the applied loading or stress regime. For each failure mechanism, the Factor of Safety is calculated as the ratio of available forces preventing failure (including the maximum structural strength) to the forces driving failure (Ryder 1969; Wyllie 2018). It is sometimes referred to as Safety Factor.

Use

The Factor of Safety is a common approach to address the uncertainties associated with the available strength of structures, the applied loads, and future changes (Ryder 1969). The Factor of Safety evaluates the state of applied stresses to strength of a structure. Values above one indicate a capacity in excess of the applied stresses. A value of one is considered as the state of Limit Equilibrium. The Factor of Safety is also used to specify safety standards for design. In this context, the capacity of the structure is designed in excess of the expected loading as specified by the design Factor of Safety.

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