Need a book?
Engineering books recommendations...
Return to index:
- To: seaint(--nospam--at)seaint.org
- Subject: Bolt retightening
- From: Kevin Below <kevinbelow(--nospam--at)videotron.ca>
- Date: Mon, 26 Sep 2005 22:48:26 -0400
I am in need of some
guidance on the right technique for retightening bolts on a 40-year-old steel
One of my clients,
suspecting that the bolts in one of their many buildings were loose, asked me to
check. Surprisingly, we found that his suspicions were founded.
The roof structure
of this warehouse type building is the Gerber type (cantilevered beams
alternating with suspended spans), and the beams that pass over the
have 4 bolts in the
connection. These bolts are almost all loose. You can unscrew them by
drawings call out hi-tensile bolts in non-slip connections, which is obviously
not what they got.
There is no bracing
in the building, and no concentric masonry walls, so I presume the lateral
resistance comes from the non-slip joints of the beams over the columns, forming
rigid connections. In this case, the beam-column connections should
rightly be non-slip, and not bearing type.
So now I have to
prepare plans and specs for tenders for the job of tightening the
My search of the
steel manuals and text books and web sites leads me to conclude that it is not
simply a case of applying a torque wrench to these bolts. In the old
Canadian steel code (oh yeah, this job is in Canada), the required torque
was specified, but now it appears that a predetremined torque does not
always produce the required bolt pretension. So each shift, the guy using
the torque wrench should calibrate his torque wrench with the type of bolt
to be installed, on a machine that measures the pretension.
My first question is
whether I should require new bolts, since I have no control or knowledge of the
existing bolts. It seems like a good idea, especially if I need to
calibrate the torque wrench.
Also, the idea of a
machine to calibrate the torque wrench each day seems overkill to me, when this
building doesn't seem to have suffered in its loose state for so long, surviving
mild earthquakes and strong winds with no sign of distress, despite its lack of
tightened bracing. Would the turn of the nut be sufficient, or is this
really only for bearing type connections ?
What do the steel gurus think
Kevin Below, ing.,
No virus found in this outgoing message.
Checked by AVG Anti-Virus.
Version: 7.0.344 / Virus Database: 267.11.7/112 - Release Date: 2005-09-26