Factor of safety (F.O.S)
Factor of safety is required to bring the structure from the state of collapse to a usable state.
It has following significances:
- The structure shouls be able to withstand the variations in expected loading up to some extent. Factor of safety covers uncertainties in forces or loads.
- At service load, deflection should be small.
- When the material used is under strength, factor of safety covers unceertainties in material strength.
- It covers, poor workmanship.
- It covers unexpected behavior of the structure.
- It covers natural disasters.
- During fabrication and erection due to storage of materials, movement of machinery and labor. Stresses are produced which may be very high. Factor of safety may take care of these loads during construction.
- Presence of residual stresses and stress concentrations beyond the level theoretically expected.
Reference : Steel structures by Zahid Ahmad siddiqi and Muhammad ashraf