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RE: Twist off bolts (was:Bolt retightening)[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: RE: Twist off bolts (was:Bolt retightening)
- From: "Harold Sprague" <spraguehope(--nospam--at)hotmail.com>
- Date: Wed, 28 Sep 2005 22:03:36 +0000
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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