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RE: Bolt Tightening

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Title: RE: Bolt Tightening

The value of 0.0167 given in the formula is actually not a constant. The Structural Bolting Handbook by SSTC reports that this value can range from 0.01 for well lubricated, to over 0.25 for poorly lubricated or rusty bolts. So, this gives a torque range from 200 to 500 ft-lbs for 3/4 in. A325 bolts. The relationship between torque and tension in high-strength bolts is highly variable. That is why the RCSC Specification does not allow standard torque values to be used, but rather requires that the wrench be calibrated using a skidmore.

        Actually, verification testing is required by the RCSC Spec. for all four installation methods (turn-of-nut, calibrated wrench, tension control bolt, and direct tension indicator). For more information, you can check out the new 2000 bolt spec at
If it is not currently available for download, it should be soon and you can request to be notified via email when it does become available.


 -----Original Message-----
From:   Evan Jorgensen [mailto:EJorgensen(--nospam--at)]
Sent:   Tuesday, January 23, 2001 11:05 AM
To:     seaint(--nospam--at)
Subject:        Re: Bolt Tightening

The formula that I have seen, for the relationship between torque and tension,

T = (0.20*F*D)/12 = 0.167*F*D

where:  T=torque (ft-lb)
        F=tension (lb)
        D=diameter (in)

However, I agree that DTI's are the best method for tensioning bolts.

 "c2" <jimmycccccc(--nospam--at)> wrote:

>I am well aware of the requiments of RCSC pertaining to the proper
>tensioning of A325/490 bolts.  I found it prudent to read the same materials
>that field inspectors do a long time ago.  It would have been like a battle
>of wits with an unarmed man if I did not.
>It is my understanding that research has established a direct relationship
>between bolt tension and torque values.  As a matter of fact there is a
>formula (which I wish I could recall) reliabily predicting approximate bolt
>tension based upon thread pitch, bolt diameter and applied torque.  If I
>remember correctly the proper torque value for a 3/4 inch A325 bolt is 225
>foot pounds.  This WILL induce the correct amount of bolt tension when the
>bolt is installed with a hardened washer under the turned element.
>Likewise, so will the practice of turning the nut from a snug tight
>condition some 1/3 to 1/2 turn more.  As a practial matter in the field the
>bolt is usually turned somewhat less than a full turn..
>My considerable experience with Skidmore calibrated wrenches, obstinate
>ironworkers and incompetent field inspectors leads me to say that this
>method is somewhat less than satisfactory under any circumstances less than
>near laboratory conditions.  That which works well in the lab often fails
>miserably under field conditions.  I have previously enumerated some of the
>many variables that affect the desirability of utilizing this method, the
>paramount one being the lack of inspector confidence level and mutual
>satisfaction that the bolts have been uniformly correctly tensioned.
>Direct tension indictors have the unique characteristic of being the only
>method by which an ironworker and a inspector have the same simple tools by
>which to gauge the quality of work being performed.  One can furnish an
>ironworker with a feeler gauge to check his work with as he goes along and
>he soon develops the "hang" of the operation without having to recalibrate
>his tool every two hours.  When the worker gets through he knows that the
>inspector will be using the same thickness of feeler gauge that he used.
>This aside from the fact that an inspector can check a far greater quanity
>of bolts in a given period of time than by any other method.  The confidence
>level on both ends just soars.
>The name of the game is to produce a properly tensioned connection with
>maximum efficiency to the mutual satisfaction of all parties.  As I have
>said "a tensioned bolt is a tensioned bolt".
>I see you missed my attempted humor in offering pre-flattened tension
>indicating washers to the steel industry. <g>
>Jimmy  C.......(hisself)

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