Factor of Safety in buildings or other construction is kept so that to compensate any uncertainty in the design process. The uncertainty could come from anywhere in the design process including calculations, material strengths, environmental conditions, natural phenomenons, duty of the structure and last but not the least quality of materials used. Though there exist some difference when viewed in technical perspective but factor of safety can also be termed as Margin of safety or even Reserve strength.
Following are some key points
- Actual loads may differ from those assumed
- Actual loads may be distributed in a manner different from that assumed
- Actual structural behavior may differ from that assumed, due to lack of knowledge or experience
- Actual member dimensions may differ from that specified
- Reinforcement may not be in proper position
- Actual material strength may differ from that specified
- Effect of previous construction, drainage, unskillful labor etc
The ratio of Strength of material to the load it is designed for.