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RE: Bolt retightening

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Kevin,

 

I doubt that there is any lubrication left on the bolts, so retightening “as is” may be difficult because of high torques if these are larger bolts (say 7/8” or more). They’d need to remove the bolts to relubricate. If the head markings do not make it obvious what was installed, replace them with new bolts. If these were black A325 bolts, have them run the nuts all the way up the threads, and if they go, reuse should be permitted (after relubrication). If A490 or galvanized, replace.

 

I’d suggest re-installation using the turn-of-nut method (when using either existing or new bolts), or twist-off bolts as an alternative if you replace the bolts. I’d avoid anything that requires wrench calibration (calibrated wrench).

 

Download the 2004 RCSC Spec at www.boltcouncil.org.

 

Bob Shaw

SSTC

 


From: Kevin Below [mailto:kevinbelow(--nospam--at)videotron.ca]
Sent: Monday, September 26, 2005 10:48 PM
To: seaint(--nospam--at)seaint.org
Subject: Bolt retightening

 

I am in need of some guidance on the right technique for retightening bolts on a 40-year-old steel structure.

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 columns

have 4 bolts in the connection. These bolts are almost all loose.  You can unscrew them by hand.

The original 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 bolts.

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., Ph.D.

 

 


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