I know what you're saying..... I respect your point of view and it's true
that lab and actual field work sometimes aren't quite simpatico..... and
yes, I've had the displeasure of stopping a job until they could locate a
Skidmore unit (which they did from a local rental.... who hadn't properly
calibrated the unit as requested by the manufacturer)and it was all they
could do with about a ~4' (or maybe it was a little longer) length torque
wrench to get what the designer had asked them to achieve in terms of
pretension..... I was not a popular guy at the job site that day........
Use of an alternate method (tension indicating washer or snap-offs) is
obviously the simplest from a field implementation standpoint...... I don't
believe that research has fully established a relationship between torque
and tension due to the many variables that affect the torque as it relates
to tension..... I think there are some general guidelines but if one truly
chooses to use the turn of the nut method I think you're obligated to follow
the RCSC Code....... if you don't you're assuming a liability.......
And yes.... I missed your joke..... I'm not the most observant dude at
times......or maybe I thought you truly came up with a method where the
washer "swells" (starts off flat) until the proper pretension is
achieved.... yeah..... that's it..........
Robert C. Rogers, PE
From: c2 [ mailto:jimmycccccc(--nospam--at)email.msn.com
Sent: Monday, January 22, 2001 2:42 PM
Subject: Re: Bolt Tightening
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>
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