A325 N and A325 X

[MaThomas565]

I understand that A325 N means threads are included in shear plain and A325 X means the threads are not included in shear plane.
My question is when would you want to have the threads in the shear plane? Doesnt that effect the connections strength?

When the threads are in the shear plane there is less material and that means less strength. So why include them in
the shear plane? I would think X would be more suited for a stronger connection.

 

[manstrom]

X is a stronger connection. Sometimes, it is unavoidable and there are threads where you don't want them, so the values are given. Sometimes, you don't have control over how they will be installed. Bolt dimensions are pretty standard.

I typically use the more conservative values for bolt size unless I know for sure it can be X.

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

 

[Lomarandil]

Right, X is a stronger connection. But it requires the contractor to pay attention to the grip length for each connection and match that to the bolt shank length. If you've got a bunch of cookie-cutter connections, that may not be an issue. They figure it out once when they order the bolts.

If you have a bunch of unique connections with different grip dimensions, or perhaps a unique grip thickness with a tight tolerance on the total bolt length, getting the right bolt in the right place to create an "X" connection may not be possible or practical. If the connection can tolerate an N structurally, that'll save your contractor money and time.

I also follow Manstrom's practice, and only rely on the N value unless I'm sure the contractor is able and willing to provide the extra legwork for X.

 

[SteelPE]

I agree with the above, always use N unless you will know for sure that your can use and X type connection (if 16 years, this has never happened). I attended a seminar once given by an engineer who worked for Cives. Here, the engineers had software they created that would guarantee that the right bolt lengths were used. The size and types of bolts were figure out during the estimating phase even before they were awarded the job.... so they claim.

I have worked with enough of these guys to know that the last thing I want to worry about is if I have specified N or X bolts on a given project.

 

[mrsutton]

You would in generally always want threading Xcluded from the shear plane since that is an area of bolt with smaller net cross section--however in many cases the bolts are overdesigned and it doesn't matter (so Ncluded is OK). It all depends on your calcs.

 

[Ron]

To achieve "X" conditions, requires almost threading a needle! The thickness of each section must be known exactly so that you achieve appropriate tightening (clamping force), without reaching the end of the threads. Difficult to do in building construction.....ain't buildin' a watch!

 

[tstructural]

Since you don't know what the contractor will do I always assume threads included. If for some reason you HAD to use the excluded values to make a design work I would add a specific note to that detail for that connection and maybe even require special inspection on that detail.