The ratio of the buckling loads to the applied loads is the factor of safety against buckling (BFS). The following table illustrates the interpretation of possible BFS values:
| BFS Value (factor of safety) |
Buckling Status
|
Notes
|
|---|
| 1 < BFS
|
Buckling not predicted
|
The applied loads are less than the estimated critical loads. Buckling is not expected.
|
| 0 < BFS < 1
|
Buckling predicted
|
The applied loads exceed the estimated critical loads. Buckling is expected.
|
| BFS = 1
|
Buckling predicted
|
The applied loads are exactly equal to the estimated critical loads. Buckling is expected.
|
| BFS = -1
|
Buckling not predicted
|
The buckling occurs when the directions of the applied loads are all reversed. For example, if a bar is under tensile load, the BFS should be negative. The bar will never buckle.
|
| -1 < BFS < 0
|
Buckling not predicted
|
Buckling is predicted if you reverse all loads.
|
| BFS < -1
|
Buckling not predicted
|
Buckling is not expected even if you reverse all loads.
|
Generally, a structure can have both positive and negative buckling factor of safety. For example, imagine a cylindrical vessel under internal pressure supported by columns. The vessel will never buckle as it is under tension, however the columns may buckle as they are under compression.
Calculating Buckling Loads
To calculate the buckling load(s) for a mode, multiply all applied loads by the BFS for that mode. For example, suppose that you applied the following loads:
- A force of 500 lbs on face 1, and
- S pressure of 250 psi on faces 2 and 3
and the buckling factor of safety for mode 1 is calculated to be 2.3, then buckling in mode 1 will occur if you apply:
- A force of 500 X 2.3 = 1150 lbs on face 1, and
- Apressure of 250 X 2.3 = 575 psi on faces 2 and 3