Safety factor calcuations

[imafastenerguy]

Are there standard calculations for determining safety factors? I am primarily interested in screw connections to steel.

I often see safety factors from 2.5:1, 3:1 to the standard 4:1.

How can calculations be done to show allowable loads with a FS lower than 4:1 be acceptable - that is assuming the test data is such so that the SD could allow this be done.

 

[MintJulep]

Safety factors exist to cover the gap between the idealized assumptions that calculations are based on and the far from ideal real world.

For threaded fastener joints some of the many things that fall into that gap are:

An understanding of the actual loads.
The preload of the fastener actually achieved in the application vs. the specified torque that you probably looked up in a handbook.
The actual surface conditions of the joined materials.
Friction (in many places)

A high degree of confidence about your knowledge of these and many other factors in the real-world can justify use of a lower safety factor.

 

[paddingtongreen]

Where are you? what codes do you use?

Generally, the code govern your safety factors.

Michael.
Timing has a lot to do with the outcome of a rain dance.