Adding two nuts to the bolt connection 1

[patelam]

Got to know from the Construction Engineer that it is a normal practice to use two nuts in regular bolt connection (non-pretension or non-slip critical).

My questions are:-
1. Is it really a normal practice to use two nuts in regular bolt connections?
2. Are both the nuts snug-tightened? Or the first nut (close to the steel) will be loose and only the second one (near the bolt end) will be snug-tightened?
3. I have known from couple of site folks that the one of two nuts are also pretensioned using turn-of-nut method even in the non-pretensioned or non-slip critical connection. But I dont remember which nut he said would be pretensioned. I am guessing it would be the second (outer) one that will be pretensioned. Is it the normal practice to pretension the bolt? And if the outer bolt is pretensioned, can the pretension stress reach within the grip length of the bolt and interfere with other loads?

 

[WesternJeb]

Seems like a way to money launder to me...

I have spec'd this out before in vibration applications specifically, but that is about it. I can't think of another application where this is required for bolted connections.

 

[dik]

Catch the link:

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

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dauwerda]

If "regular bolt connection" is referring to a structural steel bolted connection using A325 bolts (designed per AISC/RCSC), than no, it is not normal. In fact, it would be highly unusual as A325 bolts have a relatively short thread length that would generally be shorter than two nuts. As long as it is a typical joint (just steel, no gaskets or anything) pretensioning a single nut has essentially the same effect that providing a second nut does when it comes to preventing unwanted loosening.

Two nuts may start becoming a solution for non standard joints (such as through-bolting HSS, or anchor rods to concrete) as these joints can't be properly pretensioned (HSS will crush and deform, anchor rods can initially be pretensioned but the preload will relax over a relatively short time period due to concrete creep). In these cases two nuts can be used and tightened against each other to prevent loosening. When this is done it is generally not A325 bolts that are used (anchors would generally be F1554 while A449 or A354 are often used for long bolts in HSS, which don't have the short thread issue that A325 bolts have.)

 

[dik]

I should have added... I prefer Loctite Red in lieu of a jam nut.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Lion06]

The only time I use two nuts on a connection is when it's a slotted hole and I want to allow the bolt to slide in the hole. The first nut get finger tightened and the second nut gets tightened against the first. It's literally the only time I can think of that I ever use two nuts... for a bolt.

 

[dik]

Even for slotted holes, I still prefer Loctite Red. I don't like jam nuts. I also encounter hanging connections for mechanical equipment where the bolts are loaded in tension... Loctite Red, or peen the threads...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik