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RE: Repost...TC Bolts

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Thanks David for a very thorough answer to my question!

Jim K.

-----Original Message-----
From: David Sharp [mailto:Ausgang(--nospam--at)e46fanatics.com]
Sent: Thursday, June 12, 2003 11:29 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Repost...TC Bolts


Jim K.

I'll take a different tack.  How about in any connections you don't wish to
have constrained or highly tensioned --- that you allow the TC bolts ---
provided the are installed only 'snug' tight.  i.e. They must NOT have the
tips snapped off.  Sure, you can't visually tell anything about the level of
tension --- but nor could you with a standard hex product at 'snug'.

Slip-critical is a different story.  It has been my experience that very,
very few contractors or erectors understand the importance of preserving the
surface finish on TC bolts to ensure they can create SC connections.  It is
all-too common to find the cans with lids off and full of dust, dirt, or
rain water.  Similarly, the bolts are very often 'left in snug' for an
extended period of time (days) during which other members are erected and
made plumb.  Meanwhile, exposure to the elements reduces the tensions
subsequently attained when the preset-torque necessary to sever the tip is
applied.

Hence, I promote the use of DTIs and TCs together in SC connections.  The
contractor gets his fast, easy, quiet installation.  The engineer/inspector
get direct evidence that the torque it took to snap the tip was sufficient
to generate required tension.  Inspection is still easy, but at least it
becomes a 'value added' process when directly correlated with tension,
rather than indirectly as when established by torque (severed tips) alone.

Keep in mind, the torque/tension relationship is a +/- 30% relationship
under ideal laboratory conditions.  So even exceptionally good housekeeping
and installation practices can still result in a few undertensioned TC
bolts -- as the tip is designed to snap off at the same 'torque' each time.
In other words, the contractor shouldn't be hung out to dry when the odd TC
bolt has its tip snap off prior to crushing the load indicator.  Good
housekeeping and installation practices will be rewarded with a small
punch-list, and conversely not preserving the finish on the TCs until fully
tightened will result in a punch-list longer than Don Giovanni's babe-list.

With respect to the installation tools, I think you will find the 120 V
electric-driven tools used with TCs to be ideal for minimizing noise on a
hospital project.  FWIW, there are electric driven tools available for
hex-head structural bolts as well.

One last point.  A big factor on how smoothly things will go in use of TCs
in SC connections is bolt diameter and strength.  1" and above diameters
tend to be very challenging, as the typical sections being bolted with
larger diameter bolts tend to be difficult to 'snug' without prematurely
severing the TC bolt tip while trying to bring the plies together.  The
types of connections made up with 1-1/8" A490s being an extreme example.

We are getting close to having an ASTM standard for A490 TCs, though you
should treat them as 'alternate design fasteners' if used before then.  For
A325s, you can require that they meet F1852.

Good luck,

David Sharp
TurnaSure LLC



----- Original Message -----
From: "Kestner, James W." <jkestner(--nospam--at)somervilleinc.com>
To: "SEAINT" <seaint(--nospam--at)seaint.org>
Sent: Tuesday, June 10, 2003 11:07 AM
Subject: Repost...TC Bolts


This is a repost from several weeks ago. I did not see any responses.
Forgive me if I missed them.

I have a project where all the beam connections are designed with bolts in
bearing. The wind bracing is designed with slip critical bolts.

The erector would like to use TC bolts for the entire project. This is a
hospital and from what I understand the TC bolts are quiter than torquing
conventional bolts (for the slip critical connections). The entire building
is going to be fireproofed (so the steel will have no paint).

It seems to me that we should use conventional bolts for the bearing
connections and TC bolts for the slip critical connections, and not TC bolts
for the entire project. I would rather have the conventional bolts,
installed finger tight, and therefore able to slip into bearing at lower
levels of load (like when the building is under construction) rather then TC
bolts highly torqued that then are required to slip at higher load levels
(like after the building is occupied). I don't really know if using TC bolts
for bearing connections can contribute to bolt banging (after occupancy),
but I certainly want to avoid any possibility of this.

In addition, we have some shear tab connections with short slotted holes,
that are designed for higher loads (than those shear tabs with standard
holes). It seems that it may be possible to overstress some welds and plates
if those connections were installed with highly torqued slip critical bolts
instead of bearing bolts. Also, we have some connections to the existing
building where we have slotted connections for expansion where we definitely
do not want TC bolts (because of the unintended restraint that could be
provided).

Any thoughts or comments would be appreciated.

Jim K.


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