What would you regard as snug tight?
Snug tight is defined by the AISC/RCSC as when all the plies in a connection have been pulled into firm contact by the bolts in the joint, and the bolts have been tightened sufficiently to prevent removal of the nuts without a wrench. They go onto say that this is typically achieved by a few impacts of an impact wrench, the application of an electric wrench until it begins to slow, or by the full effort of an ironworker with an ordinary spud wrench. Additionally, they admit that large or thick plies or those with large burrs or uneven areas may not be able to be pulled into firm contact, but that is not necessarily detrimental to the performance of that joint. So snug tight is a bit of a vague terminology. The AISC has tried to define it as best they can, but it does leave a bit of room for interpretation and may vary from application to application. Keep in mind, this applies to all steel connections only. If there are compressible materials in the joint (like gaskets or other flexible materials), then more application-specific evaluations should be performed.
What about when a bolt connection uses a thin/thick jam nut arrangement. Should they both be tightened “snug tight”? Or is the inner nut “finger tight” then the outer nut “snug tight”?
@Russell- In structural or anchorage connections, typically the first nut is tightened as normal (the tightness will depend on the application) and then the second nut is snug tight against the first nut to keep it from moving.
A calibrated wrench stall automatically and prevents the bolts from torque failure, and this method prevent nuts from becoming loose.
hopefully that is true, but irregularities in the steel plates, and burrs, and other barriers to becoming nested one to another, are potentially going to close up, perhaps with building loading or flexion, and a tightly torqued bolt will undoubtedly be ‘less’ torque after it settles. I see why AISC allows for some interpretation in the field and some ‘gaps’, to be allowed, since, as you point out, an ironworker who tries to pull huge tonnage on a bolt to close a tiny gap to be ‘snug’ could be extensively overstressing the bolt, to failure, or nearly failure, past the yield point, making it less strong than if he simply left it as properly torqued.
You make a good comment. But, a standard spud wrench with a full force of a strong man, should be enough for a snug connection. Warning is well taken, to use a ‘not greater than’ force set into a torque wrench, which takes away the subjectivity of the above AISC statement/definition. Clearly pounding on it with an unlimited air wrench or a 10 foot long cheater pipe on the spud wrench end, is not a good answer to a slight gap in a ‘snug’ connection.
Similarly we have the turn-of-the-nut-method. Which is ‘wrench’ tight plus a quarter turn, or wrench snug, plus a quarter turn. Its the quarter turn that is essentially what you are saying, in that universally most bolts are well tensioned, in their elastic range, when a 1/4 travel is achieved after it is tight. Its been shown that turn of the nut method results in a pretty universal torque across the entire connection.
Of course this always brings up the old comedy saying, of a well seasoned ironworker telling an apprentice that connections are “as tight as you can possibly get it with your wrench, plus a quarter turn…….” Which is it? That’s why they invented snap off bolts, and load indicating washers, i suppose, Huh?