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# Margin of safety for separation, NASA-STD-5020

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## Margin of safety for separation, NASA-STD-5020

(OP)
Hi,
I am trying to figure out the margin of safety for joint separation that I can allow in my structure.
The structure is a school-book example of a bolt connecting two flanges.

The standard (page 38, equation 6-23):

So far I've determined my minumum preload, FF (1.15) and FSsep (1.2).

What does PtL (limit tensile load) mean exactly? How is it calculated?

S
Replies continue below

### RE: Margin of safety for separation, NASA-STD-5020

I only got 1/2 way through your attmt, but surprised I could see no discussion about prying loads; possibly assuming that if the joint faces are clamped then no moment, though it's better to show this with sums. This is important if you've got a typical tension fitting where the single bolt is offset from the far field loadpath (draw a FBD).

another day in paradise, or is paradise one day closer ?

### RE: Margin of safety for separation, NASA-STD-5020

(OP)
What you write seems likely. Still, I would like to know how close I can be to contact separation and say fulfils the acceptance criteria.

Right not I'm leaning toward just using another general load factor.

Separation load / 1.5 = allowed load

The NASA way would be preferable since I believe that the load factor 1.5 is too conservative.

### RE: Margin of safety for separation, NASA-STD-5020

PL is the limit applied load ... the applied load from limit loadcases. They'd use ultimate load to size the joint, that is the 1.5 factor (ultimate FoS).

another day in paradise, or is paradise one day closer ?

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