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Re: Structural Bolt Torquing Question

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Eric,

One area where you may have seen a 'specified torque' value is as a maximum
permitted value during 'Rotational Capacity Testing'.  Such tests are
conducted without regard to the intended method of tightening in the actual
structure.

These tests, which are a regular requirement for Bridgework, test structural
bolt assemblies for compatibility ---- usually but not always ---- after
plating.  During this test, fastener sets are subjected to a modified
turn-of-nut procedure which is essentially twice that used to install the
fasteners in an SC joint.  Among other things, the test verifies that any
over-tapping of the nuts to accommodate plating doesn't result in stripping
under normal or reasonably anticipated circumstances.

During this test, there is a maximum torque value that must not be exceeded.
The rationale behind the torque maximum is that  excessive torque is
correlated with inability to fully tighten a structural fastener before
fracture.  Naturally, this is due to the fact that fracture during bolt
tightening is an event resulting from the cumulative sum of torsional and
tensile stresses.  Thus, high torsional stresses diminishes our ability to
attain the beneficial and necessary high tensile stresses of an SC
connection.

Although this 'maximum torque' will vary by diameter and grade, it is based
on this criteria: Torque must be less than or equal to 0.25 PD.  (P=preload
measured tension, D= bolt diameter)

Other than this fundamental relationship, torque is a rather imprecise means
to establish anything usefully related to fasteners.


David Sharp
TurnaSure LLC


----- Original Message -----
From: "Eric Green" <EGreen(--nospam--at)walterpmoore.com>
To: <seaint(--nospam--at)seaint.org>
Sent: Thursday, October 10, 2002 4:00 PM
Subject: RE: Structural Bolt Torquing Question


This is where the question came about. The specification gives torque
information when using the turn of the nut method (Table 8.2), but gives
no information for torque when using torque control.

I realize the specification does state that the minimum tension should
be equal to 70 percent of yield and I certainly understand how to
calculate pre-stress from torque. I guess my question more accurately
stated would be:

Who specifies K so that the relationship between torque and tension can
be determined? Surely one does not depend on the contractor for this
information? Is it determined by the testing lab for each type of bolt,
nut and thread compound (if used)?

Eric Green
- Fighting my ignorance since 1964.

-----Original Message-----
From: LaCount, Curt [mailto:Curt.LaCount(--nospam--at)jacobs.com]
Sent: Thursday, October 10, 2002 1:33 PM
To: Seaint (E-mail)
Subject: FW: Structural Bolt Torquing Question

Eric,

The answer is that nobody specifies torque.  The engineer should however
specify the tension by referencing the "Specification for Structural
Joints Using ASTM A325 or A490 Bolts".  This is commonly done from the
structural notes or in the specifications.  The installation is also
subject to special inspection.

Curt La Count
Jacobs Engineering
Portland, OR

-----Original Message-----
From: Eric Green [mailto:EGreen(--nospam--at)walterpmoore.com]
Sent: Thursday, October 10, 2002 8:59 AM
To: seaint(--nospam--at)seaint.org
Subject: Structural Bolt Torquing Question



Excuse me for what is probably an obvious question for those of you who
deal with these connections on a regular basis:

Who normally specifies the required bolt torque for a slip-critical
connection? The bolt supplier, steel fabricator or the engineer? Or is
it some other party?

Eric Green
- my ignorance is my own, not my employers.



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