Torque for Jam Nuts

Date 02-28-2006 15:37

What grade of bolt are you using? and what configuration? are the bolts in bearing? or in shear? slip critical? etc.....many factors to consider depending on if the bolts are just snug tight or pretensioned.
John Wright

edit: Part 7 of the Steel Construction Manual (13th edition) by the AISC can give guidance in choosing the correct criteria for your application.

By PA

Date 02-28-2006 15:47

Hi, Thanks for your reply.

I am using (Grade 5) 3/4" A325 Hex Head Cap Screw with Jam Nut and Washer. Bolt is in Shear.

I did check in AISC manual but did not get for Jam Nut.

I am not sure but was told that because of thickness and only few threads take part in joint, the torque will be less.

Once again thank you very much for your reply.

PA

By CHGuilford (****)

Date 02-28-2006 17:38

Are you using standard A563 nuts with your bolts and then installing a jam nut or using a washer and jam nut only with the bolt? I read your post as the latter but wanted to check.
I don't believe the AISC specifications address jam nuts for bolt installation, in which case the specifications wouldn't apply.

I think that you won't be able to achieve the proper bolt tension unless you use the appropriate nut. There are not as many threads to distribute the forces over so threads would be damaged if you try to achieve minimum bolt tension.
Snug tight doesn't require minimum bolt tension so there is nothing to relate to minimum torque values in that condition.
If you are trying to achieve snug-tight condition with a 'low profile' nut, then torque is irrelevant.
If the intent is simply to retain the bolt, so the bolt acts as a captured pin, then the torque value could be determined by making up a test joint.

Chet Guilford

By thcqci

Date 03-01-2006 13:36

I agree with above statements. But out of curiosity, why are you using jam nuts and not A563 nuts?

By PA

Date 03-01-2006 19:37

Hey,

It's just because customer does not have any other choice & Can't use regular nut because of vertical clerance needed for the application.

Thanks,

Regards,

PA

By PA

Date 03-01-2006 19:35

Thanks for your reply.

I know It's not good to use Jam Nut but my customer does not have choice. At the same time as per your reply, I can't get enough bolt tension. Just I wanted to to know that how I can calculate torque required if I use Jam Nut to get maximum strength for A325 3/4" Dia. Bolt?

Is there any formula to calculate?

Once again thank you for time and consideration.

regards,

PA

By CHGuilford (****)

Date 03-02-2006 15:06

Since you are locked into a non-standard situation:

There may be better ways that I don't know of, but I would try testing the fasteners in a Skidmore with a torgue wrench. That is what is normally done for structural bolting. If the jam nuts will work at all, then you will have a torque value that correlates to a bolt tension value.

As you may already know, the testing is normally done with 3 fastener assemblies (FA= bolt,nut, washers) using the lot numbers that will actually be used.
If the bolts are too short for the Skidmore, then I would test the jam nuts with longer bolts and with a DTI washer (direct tension indicating washer). That should provide torque and tension values along with an average DTI gap. Then test the shorter bolts in a mock joint with the DTI. Apply the torque and measure the DTI gaps to see if they are equal to or less than what you tested on the Skidmore, which will be a way to measure bolt tension.

Because the jam nuts will be used in an unusual application, I would test more than 3 FA's. An arbitrary number that comes to my mind is to look for 10 FA's with consistent results. I don't believe you will see exact numbers from test to test, simply because there are fewer threads to work with so forces on the thread will be higher and more erratic. (It is hard enough to get consistent numbers when doing the tests with standard nuts.) But you should get a reasonable average to work with.
I would be concerned about the fasteners relaxing (threads yielding) some time after installation.

My other alternative, since you mentioned that the bolts would be in shear, would be to sub-drill the holes, assemble the joints, then ream to provide a hole that is no more that 1/32" over the bolt diameter. It seems that should limit the bolt/joint movement.

Those are just ust some thoughts, so please do not take any of this as authoratative information. And please let everyone know how everything works out.

Chet Guilford

By PA

Date 03-07-2006 14:43

Hey Guys,

Thanks everyone for comments and Chet in perticular.

Yes I and my buddy in workshop did the testing and we got the result beyond my imagination. For 3/4" Jam Nut, we got up to 170 FT-LB torque which is more than sufficeint for my application. We tested 10 times and got an average for our use. We did this testig with standard washer and got the result.

I know it's not good to use Jam Nut every time but it's good experience.

Thank you all again and have a great day!

PA

By CHGuilford (****)

Date 03-08-2006 22:21

PA
You are welcome for the help. Your application was interesting and I never would have guessed that you could achieve the required bolt tension with a jam nut. Thank you for following up with your results.

Chet

By billvanderhoof (****)

Date 03-03-2006 07:01

I have no idea what sort of code hassle this may involve, but if there is enough material you could tap the holes in the part and screw the bolts directly into that,
bill

By vonash

Date 03-03-2006 22:57

One (1) divded by 60 X .750 X 28,000 = torque in ft/lbs; approximately 355 ft/lbs on your torque wrench. For this type of nut I recommend "turn-of-the nut" tightening:
1. Snug the nuts with a spud wrench; use rotational tightening procedure.
2. Mark the nuts at 12:00 position; mark the column/beam/piece at 12:00 and 4:00 positions.
3.Turn the nut from 12:00 position to 4:00 position.
The bolt will be properly tensioned.
4. Chet's post is right on.

By webbcity (***)

Date 03-04-2006 03:50

two things that come to mind are if you use anti-seize the galling action of the threads is overcome to get a better torque reading . and if you do a test don't use those fastners over because of the stretch of the fastners after torque . hope this helps willie

By vonash

Date 03-05-2006 02:49

Right,
That's why we recommend marking the nuts and turning to the required azimuth.