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Re: Repost...TC Bolts

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A rose by any other name is still a rose.  An ASTM A325 Bolt is still an
ASTM A325 Bolt, regardless of whether it's designed with "N", "X", or "SC"
shear strength; pretensioned, snug-tight, or left without any nut attached
(not suggested or recommended).  As for "bolt banging", that is a phenomenom
that occurs when the bolts are left snug-tight and then slip into bearing
under service load, it is less likely with ASTM F1852 Bolt (a.k.a. TC, LIB,
twist-off, etc.).  Truely "slip-critical" connections rarely occur in normal
buildings, whereas there are some connections that require pretensioned
bolts.  There is no reason why pretensioned bolts can not be used where
snug-tight bolts would be acceptable.  The real issue for the designer is to
properly indicate on the drawings where pretensioned bolts are actualy
required so that there isn't the chance of a disagreement in the field
between the erector and the inspector over bolts that don't need to have the
pretension verified.

I strongly recommend that all engineers invloved in the design of steel
structures obtain and read a copy of the latest AISC Design Guide #17 -
"High Strength Bolts / A Primer for Structural Engineers".  In my 30 years
in the steel business, this is one of the least understood subjects, right
up there with welding (but that's understandable - welding involves
electricity & everybody knows thats ain to voodoo).

HTH,
Scott A. Dunham, PE
Dunham Engineering Services
Dothan, AL
334-678-6948

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