AISC structure, double nut on connections... 1

[X4vier]

Anybody is suggesting me use double nuts on bolted connections for primary frame of buildings -one under the head of the bolt and one under the nut-
Is there any note or recommendation on the AISC codes that prohibits or suggests these can't be done?

Thanks.

 

[jayrod12]

Why?

 

[dik]

From my exceptions:
INSTALLATION OF ‘JAM’ NUTS (NOT RECOMMENDED):
(REFER TO:

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

THE INNER JAM NUT SHALL HAVE A THICKNESS OF NOT MORE THAN 75% OF THE OUTER NUT;
THE INNER NUT SHALL BE INSTALLED FIRST AND SNUGGED TO 50% OF THE TORQUE VALUE;
THE OUTER JAM NUT SHOULD BE INSTALLED SNUG TO THE INNER JAM NUT;
THE INNER NUT SHOULD BE RESTRAINED TO KEEP FROM ROTATING AND THE OUTER JAM NUT SHOULD BE FULLY TORQUED TO IT; AND
WRECK THE THREADS ABOVE THE NUT.


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

-Dik

 

[dik]

Slip critical and snug tight usually provide enough clamping force to prevent loosening.

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

-Dik

 

[JLNJ]

A nut under the head of the bolt? So your connection would be stud head/nut/plies/nut/nut?

 

[JStephen]

Do you maybe mean washers?
Thread length is not generally adequate to put a nut under the head, is it?

 

[SnTMan]

And why would you?

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[jerseyshore]

They must mean a double nut on the thread side, right? Or washer one side nut on the other. Putting a nut on the head side of a bolt is something my wife might do if she was the steel installer.

 

[dauwerda]

I would like to see someone get a nut all the way to the head of an A325 bolt:

Surely the question is actually about washers?
If so, it would be acceptable to use two as described, though generally not required.

 

[271828]

From my exceptions:
INSTALLATION OF ‘JAM’ NUTS (NOT RECOMMENDED):
(REFER TO:

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

THE INNER JAM NUT SHALL HAVE A THICKNESS OF NOT MORE THAN 75% OF THE OUTER NUT;
THE INNER NUT SHALL BE INSTALLED FIRST AND SNUGGED TO 50% OF THE TORQUE VALUE;
THE OUTER JAM NUT SHOULD BE INSTALLED SNUG TO THE INNER JAM NUT;
THE INNER NUT SHOULD BE RESTRAINED TO KEEP FROM ROTATING AND THE OUTER JAM NUT SHOULD BE FULLY TORQUED TO IT; AND
WRECK THE THREADS ABOVE THE NUT.

This is critical information. From what I've read, the common approach of two equal thickness nuts doesn't help.

 

[dik]

Concur... and not recommended. I design connections for metal fabricators and often come across 'jam nuts'. That's why my exceptions have these notes. I was a little puzzled about the original question. A nut under the head does absolutely nothing.

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

-Dik

 

[X4vier]

Oh sorry. Yes I was talking about washers.
Oups.
The main idea is for bolted connections on cold formed material is there any increase in capacity for using a washer on head additionally to the washer that goes with the nut?

 

[sbisteel]

RCSC Section 6 tells you everything you need to know about washers. There's no impact on capacity, but they are definitely required under the head in certain circumstances.

https://www.aisc.org/publications/steel-standards/rcsc/

 

[X4vier]

Which circumstances?

 

[dauwerda]

sbisteel gave you the link to the specification - it is a free download.

Without looking at the spec, I know that if the outer ply is sloped (like on a channel) a beveled washer is required.
Also if there is a slotted hole, a washer is required.
Finally if group 150 bolts are pretensioned and the connected material is less than 40ksi, washers are required. There are probably others, take a look at the spec.