You can just simply use our factor of safety calculator by typing in your known values for the maximum strength and design load. It will instantly show you its factor of safety. Alternatively, we can calculate the factor of safety of a building (or that plank) by dividing the maximum strength of the structure by the intended design load. We can also express this statement in the equation shown below:
Factor of Safety = maximum strength / design load
For a structure to be considered safe, its factor of safety must be greater than 1. A factor of safety that is equal to 1 means that the structure's maximum strength or capacity is equal to its determined design load. This means that the structure would fail if any additional load was applied.
On the other hand, if the factor of safety is less than 1, it means that the structure could fail at anytime, even before reaching the design load. Its maximum strength just can't support the load it should carry. This calls for a recalculation of the design to make the structure stronger, then.
We can also rearrange the factor of safety equation to determine the appropriate material for part of a structure. By transposing the design load variable together with the factor of safety variable, we'll arrive to an equation that looks like this:
Maximum strength = factor of safety * design load
This means that in order for the member of the structure to be reliable, its maximum strength should be equal to the product of its safety factor and the load it is intended to carry. To ensure this, we can choose from tables of materials strengths, such as this book the Structural Steel Members, to find material with specifications and cross-section that would result in a value equal to or greater than our calculated maximum strength.
You can also use our factor of safety calculator to determine the maximum strength by leaving it blank and typing in the values for the factor of safety and the design load.
