Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Twist off bolts (was:Bolt retightening)

[Subject Prev][Subject Next][Thread Prev][Thread Next]
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....