Thcqci,
I've thanked both you and Chet, and I can see how TC nuts leave much to be desired, but I'm a still little cloudy about the DTI; please correct me if I'm wrong- those paint-filled nubs are built to yield, yes? It seems then that instead of the bolt's elasticity serving to maintain tension subsequent to some kind of load or moment being applied to the connection the [properly gauged] DTI will compress just the same as if the nut were overtightened to the point of failing the gauge test and serve to permanently lower the tension on the bolt... isnt that a design limitation to be accounted for when engineering the structure? (I'll conceed it's a consideration beyond the scope of your responsibility)
In any event, these devices apparently warrant some discretion before they're specified, don't they?

Thank you,
D

Chet and Thcqci,
Thank you both for the energy you've poured into your explanation, and the clarity with which you both described the details. I appreciate the links that were mentioned as well.
That kind of quality response can be rare in some circles.

I hope for the sake of the future that readers will take note so questions similar to mine can be directed back to this thread... I doubt it's possible to provide anything more comprehensive to cover the subject.

thank you both, again...
d

JW,
Thanks; check your email
D

Hi Niekie,

You bring up good points but as with anything there is a procedure to follow. This might explain further.
When bolting per AISC and RCSC specs (other than snug-tight), we almost always have to do a pre-installation verification test. That involves taking 3 bolts, nuts, washers for each size length, lot number and in combinations as the bolts will be installed.

For turn-of-the-nut methods, we first snug tighten the bolts in a Skidmore. Snug tight is defined in the RCSC as "the tightness that is attained by a few impacts of an impact wrench or the full effort of an ironworker using an ordinary spud wrench to bring the plies into firm contact." I know this sounds subjective but another definition is the tightness required to attain approximately 10% of the minimum required bolt tension. In reality, the spud wrench approach is surprisingly consistent, according to the testing I have been involved with.
Granted, there is always an arm wrestler that tries to break bolts by brute force. But in the end, it doesn't seem to make much difference.
The key is that all plies be brought into firm contact to start from. As we approach the minimum required tension, initial tension values seem to "even out" so that there is a relatively small variation.

From snug tight, we turn the nut an additional amount. Usually 1/3 turn but it varies according to the ratio of bolt length and diameter, sometimes 1/2 or 2/3 of a turn. The Skidmore readings should then be at or above 105% of minimum required bolt tension (41 kips for a 7/8"dia A325 bolt).

At the same time, we record the torque value required to achieve the 1/3 turn, to be used for the inspection torque value later on. Of course accurate inspection depends on the bolts being in the same condition as tested.

Also, we may perform rotational capacity tests, or pay the supplier to do them, where the bolt is over rotated (2X the 1/3, 1/2 or 2/3 turn). During the 2X rotation, the tension may not be less than 1.15 of the req'd minimum at any point.
And the torque must not exceed a value computed as a ratio of measured tension X bolt diameter when going from snug tight to 105% of minimum.

Further, the bolts are inspected for necking down and thread failure after the 2X rotation.
All that is to verify the bolts attain 105 % minimum tension, without undue values of torque, and have sufficient ductility to compensate for reasonable overtightening, without significant 'necking down'.

During installation, after snug tight condition is attained, we mark the bolt, the nut, and the joint so we know starting and final position of the fastener. Inspection is simply to compare the marks to verify the nut was turned 2 flats for 1/3 turn. (The bolt head is held with a wrench to prevent turning while tightening.)
Alternatively, all we have to do is mark our socket at 120, or 180 degrees, line up the socket mark with a bit of spatter, dent, or make a chalk mark, and verify rotation by watching the wrench. Of course that means the inspector has to be there. Overall, the whole process is simple and fast to do.

According to the RCSC specs, if a bolt loosens during tightening procedures, all you have to do is re-establish snug tight condition and rotate the nut again. It is not considered re-using the bolt unless it is first loosened deliberately. Of course, if a number of bolts loosen in the process, then it is wise to recheck that all plies were brought together before proceeding.

It is possible the someone could 'get on with the job' but that can happen with anything. Although, if deemed necessary to do so, then applying inspection torque could be done as a check, but should be done very soon after tightening. The torque needed to turn a tightened bolt will change somewhat as rusting happens.

Chet Guilford