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.

 

[jhnblgr]

https://www.aisc.org/globalassets/modern-steel/archives/2014/12/si.pdf

https://www.aisc.org/globalassets/aisc/publications/standards/a348-20w.pdf

 

[SWComposites]

the general rule of thumb is min of 3 full threads.
and the nut material/type needs to be strong enough to fail the bolt in tension.

 

[Tomfh]

Codes often require at least one thread beyond the nut.

One thing I've noticed in practice is that if a nut and bolt aren't well machined that the nut can slip anyway, yielding the threads before yielding the bolt.

 

[HTURKAK]

I remember for structural applications (Research Council on Structural Connections Specification requirement is that the end of the bolt be at least
flush with the face of the nut).
Common practice at least 2 threads after nut.
There are previous threads for this subject.
One of them,

Standard for how many threads to be out from a nut​

 

[BulbTheBuilder]

I remember for structural applications (Research Council on Structural Connections Specification requirement is that the end of the bolt be at least
flush with the face of the nut).

yes, point 4 of chapter 8.1 of the RCSC spec. attached by jhnblgr

"The joint shall be installed to the snug-tight condition with sufficient thread engagement" pg. 16.2-60
where "Sufficient Thread Engagement. Having the end of the bolt, not including the spline of a spline-end bolt, or the available bolt threads extending beyond or at least flush with the outer face of the nut; a condition that develops the strength of the bolt."

The threads of bolts are constant and are dependent on the bolt size - SCM Table 7-14. Try to get more projected thread length means increasing the bolt length which isn't recommended. I just read Specifying Bolt Length for High-Strength Bolts by Charles J. Carter (this past Tuesday. He talked about the jamming of the nut with increased length.

In my opinion, sufficient thread engagement >=flushing is adequate to develop tension of bolts.

 

[EngDM]

We are trying to come up with a detail for supporting a threaded rod in tension, and due to material availability we are going the route of tapping our own holes in a solid square stock.

the general rule of thumb is min of 3 full threads.
and the nut material/type needs to be strong enough to fail the bolt in tension.

I guess the square stock should be a high strength steel as opposed to 44W then? Or could I leave enough net tension area around the bolt to exceed the capacity of the bolt and be fine. This assembly would have a larger tension area than your typical A325 bolt nut.