Snug tight condition

[jasem81]

Hi,
My subcontractor ios asking me to provide him with the Torque value for bolts, but the specification of the project is telling that the bolts shall be SNUG TGHTINED,AISC360 is defining the snug tight condition as the tightness required to bring the connected plies into firm contact.
I have a serious concern to do the tightening without required torque value, what do you think?

 

[Ron]

Snug tight is the initial tightening process commonly used in steel construction. It is not readily quantifiable; however once the plies have been brought into contact, additional tightening only pre-tensions the bolt. When your connection is slip critical, the next step is to either use a torque value or to use the "turn of nut" method for pre-tensioning. Many bolts in steel construction do not require additional pre-tensioning beyond the snug tight condition.

 

[ajh1]

There is no mandatory tension, or torque, value required for a snug-tight connection. The goal is to have the plies in firm contact which depending upon the fit-up of the plates may be quite easy requiring minimum torque or quite hard requiring lots of torque. Torque values for pretensioned bolts were removed from the RCSC spec in the early 1950's due to the wide variability that the condition of the bolt creates on the torque value for same tension. Dirty, dusty bolts with minimal lubricant may require torque values as much as twice what a clean, well-lubricated bolt would require to achieve a designated tension.
Basically, if the nut is on tight enough that you can't remove it by hand then it is sufficiently tight for the snug-tight condition assuming the plies are in firm contact.
To establish torque values for final pre-tensioning requires a preinstallation test as documented in RCSC Section 7.

Al Harrold
RCSC Chairman

 

[jasem81]

Thanks

 

[msquared48]

I always understood snug to mean hand tight + 3/4 turn.

Mike McCann, PE, SE (WA)

 

[WillisV]

https://www.aisc.org/DynamicTaxonomyFAQs.aspx?id=1762

 

[BUGGAR]

Mike, I think that's the valve adjustment on a hydraulic camshaft Chevy V8.
I had a job where the inspector ran around with a little go/no gage thickness gage. I don't think it had any value other than he made a big deal about it and all the erectors made sure to snug the bolts just to get rid of the guy. So in that respect, it proved to be a very functional gage.

 

[msquared48]

How did you know I used to have a '67 Chevy with a V8? You work with Homeland Security or the NSA?

Mike McCann, PE, SE (WA)

 

[connectegr]

Torque is not a term used in US structural bolting. I have attached the RCSC current wording.

Torque is effected by to many variables. Surface friction, bolt lubrication, tool calibration, etc. Therefore torque provides an inconsistent result. For bearing bolt connections the primary objective is to bring all plies into firm contact, any residual bolt pretension is irrelevant to the bolt shear capacity.

http://www.FerrellEngineering.com

Providing fabrication and erection efficient structural design of connections. Consulting services for structural welding and bolting.