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coefficient of friction

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List,
 
What would be a good reliable source of information on the static coefficient of friction for DF-L (wet, per ASTM C1028)?
 
TIA
 
Steve Gordin SE
Irvine CA
 
----- Original Message -----
Sent: Wednesday, September 28, 2005 3:03 PM
Subject: RE: Twist off bolts (was:Bolt retightening)

Tom,
That is correct.  That is why the twist off manufacturers are conservative
in the torque it takes to twist off the bolt.  Another critical factor is
the lubricant.  If you have a large complicated structure and the steel is
erected and plumbed.  Then you take a couple of weeks off because of the
rainstorms that blew through.  You need to pull a pretty good sampling of
bolts, load them into the Skidmore and verify if you are getting the
tension.  If not, you need to pull the bolts and relubricate them.  If the
bolts have surface rust, you can be off on the tension by a factor of 2.

That is why special inspection by a QUALIFIED inspector is important.  You
can make it fool proof and require the DTI washers plus the DTI bolts.  That
way you can see on each and every bolt if you have the proper tension.  When
the washer squirts, you have the tension.  And you have the ease of
installation offered by the twist off bolts which use electric wrenches and
are light and easy to operate.

I think it would be fun to take some engineers out on a site, and have them
install bolts using the various techniques.  It is also entertaining to
remove the lubricant from a few bolts and even have some with light surface
rust.  Then put them into the Skidmore and see how much tension you are
getting.  Or you can keep your clothes clean and attend one of Bob Shaw's
highly educational presentations on bolt installation.

I have done both.  I am a slow learner due to too much suds sucking as an
iron worker back in my bullet proof days of youth.

Regards,
Harold Sprague





>From: "Tom Skaggs" <tom.skaggs(--nospam--at)apawood.org>
>Reply-To: <seaint(--nospam--at)seaint.org>
>To: <seaint(--nospam--at)seaint.org>
>Subject: Twist off bolts (was:Bolt retightening)
>Date: Wed, 28 Sep 2005 14:06:16 -0700
>
>The problems with relating bolt tension with torque (i.e. calibrated
>torque wrench) were well documented in this thread.  I also understand
>DTIs are a direct measurement of bolt tension, but aren't the twist off
>bolts just another torque based method and not measuring direct tension.
>I've briefly looked at the NUCOR website, perhaps I don't understand the
>twist-off mechanism.  Please explain?
>
>Tom
>
>________________________________
>
>From: Michael Hemstad [mailto:mhemstad(--nospam--at)mbjeng.com]
>Sent: Wednesday, September 28, 2005 13:36
>To: seaint(--nospam--at)seaint.org
>Subject: Bolt retightening
>
>
>Kevin,
>
>I concur with Harold (I'm sure he's relieved to hear that).  One of the
>huge and seldom-quoted advantages of twist-off bolts is that they can be
>inspected with certainty, from the ground, with very little effort on
>your part.  If the spline is twisted off, it's done.  Therefore it is
>entirely feasible to inspect every bolt on a project.  It really adds to
>everybody's peace of mind.  And, as Harold notes, it's also probably the
>cheapest solution.
>
>I've never had to spec these bolts into a project, because they're
>universally used around here; but if I saw ironworkers using the
>old-style bolts and spud wrenches, I'd start asking a lot of questions.
>
>Mike Hemstad, P.E.
>
>Meyer Borgman Johnson
>
>Minneapolis, MN
>
>------------------------------------------------------------------------
>--
>
>From: "Harold Sprague" <spraguehope(--nospam--at)hotmail.com>
>
>To: seaint(--nospam--at)seaint.org
>
>Subject: RE: Bolt retightening
>
>Kevin,
>
>Torque wrenches are only supposed to be used in arbitration in the
>
>installation of A325 or A490 bolts according to the RCSC. Torque is a
>very
>
>poor indicator of tension in a bolt. The tension is what you are trying
>to
>
>achieve.
>
>Getting a Skidmore on the project site (hydraulic tension indicating
>device)
>
>is not a big deal for most iron workers, and is fairly routine.
>
>Because of the variability, I would NEVER allow calibrated wrench bolt
>
>tightening.
>
>When you boil it all down, the best and probably cheapest solution is to
>
>replace all of the bolts with the tension indicating bolts using the
>
>splines. The installation wrench rotates the nut while holding the bolt.
>
>The spline snaps off when the appropriate tension is achieved. You still
>
>have to install the bolts to "snug tight" with the faying surfaces in
>full
>
>contact. And you still need the Skidmore on the site to verify the
>
>appropriate tension for the tightening procedure you select. The
>
>installation is a lot easier using the twist offs as opposed to using a
>
>pneumatic wrench or a spud wrench with a cheater (for turn of the nut).
>The
>
>labor is where you will save the money over other installation methods.
>And
>
>the QC is better.
>
>If you want the ultimate in reliability, ease of installation, and 100%
>QC,
>
>use the DTI "Squirter" washers with "twist off" bolts. You get the ease
>of
>
>installation with the "twist off" wrench and you get the tension
>indication
>
>that the "squirter" washers provide.
>
>If you decide to go against my incredibly sage advice and use turn of
>the
>
>nut, use match marking with a paint stick. And never tighten bolts
>without
>
>a Skidmore.
>
>Regards,
>
>Harold Sprague
>
>
>
> >From: Kevin Below <kevinbelow(--nospam--at)videotron.ca>
>
> >Reply-To: <seaint(--nospam--at)seaint.org>
>
> >To: seaint(--nospam--at)seaint.org
>
> >Subject: Bolt retightening
>
> >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 structure....
>
>
>

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