Jam Nuts

[Logan82]

Hi!

What is the best configuration for the jam nut and the standard nut on a chemical anchor assembly (Hilti)?

This one:

Or this one:

And also, does anyone have a reference / formula / chart to know the torque to be applied on the jam nut?

 

[LittleInch]

It's actually the second one.

See

https://www.eng-tips.com/viewthread.cfm?qid=480157

and follow the link I had in that post.

But I think you can only bolt down once you have a resistance.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[desertfox]

Hi

Here is a link from bolt science showing how jam nuts should be installed

https://www.boltscience.com/pages/twonuts.htm

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Logan82]

Thank you for your replies LittleInch and desertfox!

In my case, is my concrete anchor considered like a "long bolt"?

Here is what they say about "long bolts" from the link you sent me:

https://www.boltscience.com/pages/twonuts.htm

"If there is a significant amount of fastener extension that would be developed i.e. when a long bolt is used, then using the thin nut on the bottom can be inappropriate. In such circumstances the bolt extension could be such that the thin nut would sustain thread stripping due to the extension exceeding the thread clearance available in the thin nut. Hence the warning that placing the thin nut next to joint is not appropriate in all circumstances."

 

[dik]

Tighten her until she strips, then back off half a turn. I usually tighten anchor rods to 50%, and on that basis, you should not be stripping threads. Your washer should match your bolt diameter... The jam nut should be 1/2 to 3/4 the depth of the nut on top. If that's still a concern, there's always Locktite Red... my favourite... with overhead mechanical stuff, if a failure would occur because a fastener loosened, I spec locktite...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Tmoose]

Is the jam nut Hilti's idea?
What does Hilti have to say ?? If anything.

If an insurance company was writing a policy to cover "LoOseNinG" of a nut and the various curious "locking" methods that might be applied in good conscience I think the exclusions and limitations would number in the dozens, and rightly so.

 

[dik]

I suspect jam nuts were around a tad before Hilti...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Logan82]

Hi!

The jam nut was not suggested by Hilti. A colleague suggested me to use jam nuts.

Loctite was my other option. Dik, when do you typically use jam nuts vs loctite?

Tighten her until she strips, then back off half a turn.

Are you writing this phrase about the jam nut? Why would you want to strip it?

 

[desertfox]

Hi Logan
What length is the anchor bolt you are using and what prompted the use of a jam nut?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[3DDave]

"Tighten her until she strips, then back off half a turn. " is a joke.

Similar with putting the maximum number of turns into a rubber band on a model airplane - wind it til it breaks and then back off one.

 

[3DDave]

If the fastener is long enough a jam nut is redundant. The jam nut is to preclude turning of the main nut and in a long fastener the movement required to allow the main nut to turn is far greater than should ever happen if the nut and fastener were sized correctly (60-80% of elastic limit) so that turning won't happen.

The more typical use is when the elongation is small and the possibility exists for the main nut to be relieved of load and free to turn. Generally that is sign of a bad design and a jam nut is used because people are unable or unwilling to change the design. For example - an adjustable stop screw that cannot have the stop load on it all the time.

 

[dik]

I almost never use jam nuts... nearly always locktite...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[dik]

my feeble attempt at humour... it's same as tightening nuts... tighten her till she cracks and then back off half a turn... or model airplanes.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Logan82]

What length is the anchor bolt you are using and what prompted the use of a jam nut?

The anchor threaded rod has a length of 600 mm. I was seeking solutions to prevent anchor loosening.

"Tighten her until she strips, then back off half a turn. " is a joke.

Haha ok!

3DDave and dik, thank you for the information.

 

[desertfox]

Hi Logan82

One way you can ensure the nut doesn’t come loose is weld a block adjacent to the nut after it’s been tightened see sketch

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[canwesteng]

I don't think the conclusion of the article is to never use jamb nuts? I think a jamb nut is fine in this application, since you don't necessarily want the fastener to elongate as that may exceed the bond strength of the epoxy. Similarly, if it were a headed anchor and you wanted to preclude side face blowout. I wouldn't plan on putting torque beyond install torque on anchorage that isn't sleeved. If it was steel to steel, it's of course no problem to make the nut tight enough that it can't loosen, the use of two nuts is always appropriate when you don't want a clamping force between the materials being fastened.

 

[r6155]

See PIP Process Industry Practices Structural STE05121 Anchor Bolt Design Guide.

Regards

 

[JLNJ]

How about an Anco Lock Nut instead?

http://Www.lok-mor.com

 

[Logan82]

canwesteng, the difference between long bolts and anchors that you are pointing to is a good point.

r6155, it's great to see a reference book where they talk about the use of two nuts on anchor systems:

JLNJ, thank you for the suggestion, I had not heard of this model of nut before.

 

[dik]

I almost always spec Grade 55 S1 material for anchor rods, even if the client wants A307...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik