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Re: Shear-off bolted connection

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The "official" name for this product is a twist-off-type tension-control
bolt assembly. I call them TC bolts for short. Many manufacturers make
them as you can see just by looking through the ads in any issue of
Modern Steel Construction.

This product is an assembly that consists of a bolt with a splined end
and nut. The bolt head is usually a button head that is sized to
eliminate any need for a washer, but some manufacturers make this
product with a hex head. A washer is normally included in the assembly
under the nut. The splined end is specially designed by the manufacturer
to shear (twist) off at a defined torque. Because the installed
pretension can vary significantly for a torque due to the condition and
match-up of the assembly, the TC bolt assembly must be purchased and
supplied as an assembly with lubrication by the manufacturer.

The Research Council on Structural Connections, which writes the
Specification for Structural Bolts Using ASTM A325 or A490 Bolts,
currently addresses this product as an alternative design fastener. That
is, it is included as a special assembly that meets the basic intent of
ASTM A325 (or A490), primarily because there hasn't been an ASTM
specification that covers the product. However, ASTM is about to publish
a specification F1852 that covers twist-off-type tension-control bolt
assemblies that are the strength equivalent of conventional ASTM A325
bolts. The marking system on the head of the product is still A325 to
simplify things. The next revision of the RCSC Specification will most
likely include them in this form, rather than as alternative design

Per the RCSC Specification, TC bolts are suitable for use in snug-tight
joints and pretensioned joints (bearing and slip-critical). Note: TC
bolts can be used in snug-tight joints even if the splined end is
sheared off (i.e., with pretension in the installed bolt) because the
whole point of a snug-tightened joint is that it doesn't matter what the
installed pretension is in the bolts in a snug-tightened joint. But
that's another subject.


Robert Rollo wrote:
> does bethlehem still mfr the LIB system, with the ingersol rand tool ?
> are they compatible ?
>      -----Original Message-----
>      From:   Harold Sprague [SMTP:harold.sprague(--nospam--at)]
>      Sent:   Thursday, January 14, 1999 12:40 PM
>      To:     'seaint(--nospam--at)'
>      Subject:        RE: Shear-off bolted connection
>      Contact the LeJeune Bolt Co. in Minnesota @ 800-872-2658.  They
>      handle the
>      bolts and the installation tools.
>      Regards,
>      Harold Sprague, P.E.
>      The Neenan Company
>      harold.sprague(--nospam--at) <mailto:harold.sprague(--nospam--at)>
>      -----Original Message-----
>      From: Maria I. Falconi [mailto:maisabel(--nospam--at)]
>      Sent: Thursday, January 14, 1999 11:56 AM
>      To: seaint(--nospam--at)
>      Subject: Shear-off bolted connection
>      Dear Colleagues,
>        I need to find information about a type of bolted construction
>      that
>      involves bolts that have a spigot at the end of the thread which
>      shears off
>      at tightening when the required torque is reached.
>        Special power drivers are used to install bolts in this
>      fashion.  I need
>      to find out about purchasing and/or renting these machines.
>        I got a hold of a brochure from RTB Tooling (Rapid Tension
>      Bolts) which
>      talks about these tools but I don't have enough information (no
>      phone
>      number, etc).
>        The description of how the RTB works is as follows:
>      "After the connection is fitted, the outer socket of the tool
>      applies a
>      clockwise rotational force to the nut as the inner socket applies
>      a counter
>      clockwise force to the spline.  When the fastener exceeds the
>      required
>      tension, the spline end will shear".
>        I would greatly appreciate any information on where to get a
>      hold of
>      suppliers of this type of equipment, in the States or in South
>      America.  I'm
>      looking at erecting a 10-story steel building with this system
>      (1200 tonnes
>      of steel involved) and I urgently need to price the purchase or
>      lease of 13
>      of these power drivers.
>      Regards
>      Maria I. Falconi
>      Guayaquil, Ecuador