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Snug tightness
2

Snug tightness

Snug tightness

(OP)
Can a snug be assigned with definite value of torque?

RE: Snug tightness

Not really. Snug tight generally considered to be around 150 Ft-K LB (see my post below) but it could vary a bit because snug tight means full contact between the plies. Flatness varies.

RE: Snug tightness

(OP)
Hi bridgebuster,

Does the 150ft-k approx. value vary on bolt size or dia.?

RE: Snug tightness

No.

RE: Snug tightness

I'd advise against specifying a torque valentine for snug tightness. Anything from dirty threads to misalignment can cause this to vary greatly.

Snug tight is defined as tight enough to bring all materials in full contact.

RE: Snug tightness

"Around 150 Ft-K"? Was that supposed to maybe be 150 Ft-Lbs ? Any way, torque values for structural bolts can only be relied upon for matched bolt/nut assemblies from the manufacturer. Even so, for fully-tensioned connections you would want to use squirter washers anyway to proove the preload.
Dave

Thaidavid

RE: Snug tightness

thaidavid40 - GOOD CATCH! I guess I'm so used to using Ft-K rather than FT-LB.

RE: Snug tightness

@ bridgebuster -
That happens to me too. I get so used to using kips that I sometimes forget just how much that really is!
Dave

Thaidavid

RE: Snug tightness

(OP)
Thanks everyone!...

RE: Snug tightness

Well European codes say about 10% of the full prestress of the bolt


best regards
Klaus

RE: Snug tightness

Per THE RESEARCH COUNCIL ON STRUCTURAL CONNECTIONS (RCSC):

The old definition read:
"A snug tight condition is defined as the tightness that is attained with a few impacts of an impact wrench or the full effort of an ironworker using an ordinary spud wrench to bring the connected plies into firm contact."

New definition:
"Snug tight is the condition that exists when all of the plies in a connection have been pulled into firm contact by the bolts in the joint and all of the bolts in the joint have been tightened sufficiently to prevent the removal of the nuts without the use of a wrench."

RE: Snug tightness

Actually the latest RCSC Spec (2014) reverted the definition to snug tight back to the what IFRs labels as the "old definition". While both definitions work for a snug-tight only bolt, snug-tight as a precursor to a pre-tensioned bolt with the second definition was not consistent with the rule when the turn-of-nut provisions were created and if someone used the spec turn-of-nut without doing the mandatory pre-installation testing the tension values were below the acceptable value. There is no mandatory RCSC requirement for any specific torque or tension for a snug-tight bolt, nor any inspection requirement for same.

RE: Snug tightness

Darn - I'm always one rev behind and one day late. Thanks to aj for setting me straight.

RE: Snug tightness

(OP)
Is there big impact on the structure if snug tight bolts in connections are mistakenly full tight with specified torque?

RE: Snug tightness

No, in general having a pretensioned bolt where a snug-tight would be acceptable is fine. The only caveat to that would be at a shear connection where the intent is to have a rotational capability at the joint, shear tab connection to the web of a simple span beam. Having a pinned connection may be beneficial to the design of other parts of the connection. A pretensioned bolt might create unexpected moments in other areas.

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