Thread Interception

[KZSteel]

Quick question:

When designing steel connections, it is generally always assumed that the threads of bolts are intercepted by the shear plane?

 

[slickdeals]

No, not always. You have a threads excluded from shear plane (X) case and threads included in shear plane (N) case. The X have higher values than N.

Not sure if that answers your question.

 

[paddingtongreen]

Unless using thin materials, it is difficult to get the threads into the shear planes for A325 and A490 bolts. Usually the Detailer sizes up to the next longer length from the minimum engagement, but it's not that easy even with minimum engagement.

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

 

[SteelPE]

When trying to design connections, I usually design all of my bolts as N bolts. This way I know they will be right.

However, I went to a connection seminar a few months ago. The speaker was one of the top engineers at Cives Steel. He said that designing connections using just the N value is a waste of money. He said that they will design connections using the X value if they can prove that the thickest member connected < unthreaded length of the bolt. Seems risky to me but this is something they look at when they price a job.

 

[paddingtongreen]

I was already doing that when I first did business with Cives, back in the late seventies.

Set up a spreadsheet with thread length, the thickness of the nut, the thickness of the hardened washer, subtract the last two from the first, and it will tell you the minimum thickness of the outside ply if the end of the bolt is at the face of the nut (minimum engagement). Don't measure the thread, use the tables because the run-in does not count as thread.

Standard practice is for a Detailer to go to the next longer bolt length, so it will show at least an eighth of an inch proud of the nut. If you take that out of the thread, the outside ply would have to be very thin to have the thread in the shear plane.

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

 

[slickdeals]

You may also want to look at an Engineering Journal Article by Charlie Carter (AISC) titled "Specifying Bolt Length for High-Strength Bolts"