Thread embedment required for bolt in tension

[EngDM]

Hi all,

A simple question that I have never really thought about, but if you have a bolt in tension are there any checks as far as the threads are concerned? Is there a codeified minimum number of threads (or length) to engage before getting full capacity of the bolt in tension? Is it just to the end of the standard nut size (I.e. that is how the nut lengths were determined and standardized)? Is there an equation in the event that you are not fully into the nut?

This question is moreso for tension requirements, not the intersected vs not intersected shear plane checks.

 

[Stick.]

Interesting, so the sloped threads apply an outwards pressure and if the nut is too thin then it just splits apart?

Based on what the Bolt Science link says, it sounds to be more an issue of the radial expansion of the nut/tapped piece reducing the contact between the internal and external threads, which reduces the shear area (for both internal and external threads), which increases the likelihood of thread stripping. If the nut/tapped piece is stiff enough to resist this, then it sounds like it's not a problem.

 

[EdStainless]

Or the nut enlarges enough to allow the thread engagement to become small enough to fail.
We used to test high strength bolts (>180ksi UTS).
Our test fixture was about double the OD size of a heavy nut, and it was made of tool steel.
We could develop 2d engagement, but out standard was to test at 2.5-3 threads.
Our fixture would last about 1,000 tests.

 

[EngDM]

I'll go through the links more in depth once the fabricator comes back with their ideas, but from the discussion here, it sounds like a 2" deep 1"Ø hole tapped into a 1 1/2" square block is going to be more than sufficient, especially since the block is welded between another 2-5/8" thick plates to make up a clevis.