All the Details (the fine print)
FOR IRONWORKERS AND OTHER BOLT INSTALLERS
- You can locate the DTI on either end of the bolt. Just make sure
the DTI bumps bear against the underside of the bolt head or
against a hardened flat washer, never directly against the nut or the
- Never never never grind the DTI bumps down by turning either the bolt
head or the nut directly against the DTI - put a flat washer in between.
- Always snug an array of bolts before final tightening, just
as you would when DTIs are not used. Make sure you don't fully compress
the DTI on the snug (first) pass. On the final pass, compress the DTIs
in the same sequence as you would if there were none present - that
is, from the most rigid point outward.
- If impact wrenches are used, final DTI compression should take less
than 10 seconds, or perhaps 20 seconds for larger, A490 bolts. Choose
a wrench with sufficient muscle (size, air pressure, condition) to do
this. Other types of wrenches are also acceptable, such as electric
or hydraulic, but if they're non-compacting, ignore the "10 second"
rule. See the following FAQ's (compressing DTI's,
recommended wrench capacity and make, flattening
DTI's, torque control, twist-off
- Don't try to use a feeler gage very much. Judge the DTI gap closure
mainly by eye. Remember, a "completely flattened" DTI is okay for all
but the larger A490 bolts.. Check with the inspector, or call us for
guidance. See the following FAQ's (failure or
stripping of bolts , flattening DTI's)
- You're not supposed to take more bolts out of their kegs than can
be stuffed, snugged, and tightened in one shift, (oh sure!). But just
in case keep some lubricant handy if the bolts and nuts are getting
too rusty to tighten efficiently.
- Remember, DTIs don't change the torque resistance of the bolt, and
they don't change the (flat) washer requirements either. (Regular thickness
F436 washers over short slots or oversized holes, but extra thick 5/16"
F436 washers if the bolts are A490 larger than 1" dia.). See our Special
- As with any approved bolt tensioning method, don't forget to do the RCSC's Pre-Installation Verification to make sure the bolt assembly, the bolt installer, and the wrench all work together to get the right bolt tension. If there's a Skidmore around, you might try this first on it and check the results. Show the inspector - he/she will be impressed. As with any approved bolt tensioning method, don't forget to do the RCSC's Pre-Installation Verification to make sure the bolt assembly, the bolt installer, and the wrench all work together to get the right bolt tension.
- Check all bolt, nut, flat washer, and DTI certifications for conformance
with the project specifications, especially the rotational capacity
(RC) tests, if applicable, for nut lubrication. See
rotational capacity test in FAQ's. (Remember, when DTIs are used,
every bolt gets an "in situ" RC test, because, no matter how much the
bolt/nut friction factor has deteriorated, if the DTI has been sufficiently
compressed and the bolt has not broken, the rotational capacity of the
assembly must be ok.
- Check the calibration of the Skidmore, if any, on the site, and use
it to spot check the bolts and DTIs (see #4 below). That is, on the
Skidmore, see how much compression of the DTI is indicative of bolt
tension*. See bolt tension chart in FAQ's.
- Have some .015" and/or some .005" feeler gages available which will
fit into the openings of the DTI between the DTI bumps. These are available
free from Applied Bolting and are in every keg. See the following in
FAQ's (feeler gage inspection criteria , failure
or stripping of bolts)
- Put a DTI on a bolt into the Skidmore, tighten it to a bolt tension
5 percent higher than the required minimum, (see
bolt tension chart in FAQ's), using a manual wrench, and check that
the residual DTI gap (as judged by a feeler gage) is bigger than the
project inspection gap which you will use up in the steelwork. See
feeler gage inspection criteria in FAQ's. For problems some times
encountered with this test, see inspection procedure
- Make sure that the bolt installers snug all the bolts in the connection
before final tensioning. Listen for or otherwise time the final tensioning
operation. If impact wrenches are used, the rule of thumb is 10 seconds
or less but it might take as long as 20 seconds for large diameter A490
bolts. If they're not able to tighten the bolts this quickly, tell them
to try do better. See compressing DTI's in FAQ's.
It's important for the health of the bolts. If non-impacting tools are
used, the "10 or 20 second rule" can be ignored.
- Check for too much thread stickout "above" the nuts - if it is more
than half the bolt diameter, there MAY be insufficient threads ahead
of the nut for proper bolt ductillity, and thread runout may prohibit
proper compression of the DTIs and be the cause of bolts breaking. "Zero"
stickout (bolt shank flush with top of nut) is acceptable for heavy
- With a bolt in place, check a sample of compressed DTIs using the
proper thickness feeler gage between the compressed DTI bumps half way
around the DTI (our DTIs are marked only at openings to help you judge
where to try to insert the feeler gage). If you CANNOT insert the feeler
gage all the way into the bolt shank half way around the DTI, THE BOLT
IS OKAY. If you CAN insert it all the way into the bolt shank more than
half way around, THE BOLT IS NOT OKAY. In the latter case, ask the bolt
installer to tighten the bolt a little more. If the DTI is almost compressed
enough, it is probably OK. (Remember the Skidmore test in #4 above).
Don't over inspect the bolts. See section
feeler gage inspection criteria in FAQ's.
- Remember, a completely flattened DTI is NOT cause for rejection except
by special edict of the engineer-of-record. It's possible and safe to
"completely flatten" A325 DTIs. A490 DTIs probably should NOT be completely
flattened, although this occasionally happens. If in doubt, try flattening
the DTI on a bolt in a Skidmore, and see how much bolt tension it produces.
Then disassemble the bolt after this test and run the nut down the threads
of the bolt. If too much stretch has occurred in the bolt, the nut probably
will not run more or less freely to the root of the thread. In this
case, some caution should be exercised to limit the A490 (and only A490)
DTI compression. See FAQ's ( failure or stripping
of bolts, flattening DTI's)