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

RE: RE: Washers for A490 Bolts

[Subject Prev][Subject Next][Thread Prev][Thread Next]
Tom-

You and Charlie are both correct on this one. Washers do prevent galling
during bolt installation, but this has more to do with the smooth hardened
surface of the washer than the washer thickness. Washers with a greater
thickness (5/16 in. vs. standard 5/32 in.) are required to prevent dishing
of the washers used with bolts which have high minimum installed
pretensions.  If the higher thickness were a galling consideration, there
would be no need for the RCSC to exclude using 2 standard thickness washers
to comply with the 5/16 in. requirement. The single washer requirement is
there to assure that the washer has sufficient stiffness to prevent loss of
bolt elongation at high pretensions.

-Heath

 -----Original Message-----
From: 	Tom Higgins [mailto:thiggins(--nospam--at)grpmack.com]
Sent:	Tuesday, April 17, 2001 8:48 PM
To:	seaint(--nospam--at)seaint.org
Subject:	Re: RE: Washers for A490 Bolts

Charlie,

The washers prevent galling.  Without the washers you may not achieve the
required installation tension.  If you really needed a slip-critical
installation, you probably needed the washers.  However, read all the fine
print.  High strength bolts may be used in "bearing" connections with
snug-tight installation only.  The washers really shouldn't matter much.
The character of the load is important.  t's got to be essentially static in
a "bearing" connection.  The direction of the force is also important.  It's
got to be normal to the slot within plus or minus x degrees.  Direct tension
is not allowed.  See the specification for high-strength bolts in the back
of your steel manual for details.  Use a recent edition.  They are always
fiddling with this document.

For after the fact justification, you could try a Skidmore-Wilhelm test to
show that the tension is achievable without washers.  Not likely with short
490s, though.

Tom Higgins

>>> Charlie Carter <carter(--nospam--at)aiscmail.com> 04/16 5:37 AM >>>
>On one of our projects,  1-1/2" dia. A490N bolts were specified for shear
>tab beam connection.  Because of fit-up, the contractor made the connection
>using short slotted holes in the beam web.  However, the requirements for
>minimum 5/16" thick washers were overlooked.  The beam is in place now and
>because of the existing conditions, the connection can not be accessed to
>replace the bolts and the washers. What is the reason for requiring 5/16
inch
>washers?

Thicker washers are required for pretensioned applications with A490s of
diameter greater than 1 in.because of the tendency of standard F436 washers
to dish into the hole, thereby reducing the clamping force induced using an
otherwise acceptable installation procedure.

>Can one use some reduced capacity when standard thickness washers are used
>instead of 5/16 inch washers?

One possible solution is to consider whether pretension is actually required
in the first place. If the bolts are in shear, snug-tightened installation
of A490s is often acceptable (pretension is often not required). And per
RCSC Specification Section 6.1.2, for snug-tightened bolts in slotted holes
in exterior plies, a standard ASTM F436 washer is suitable.

Hope this helps.

Charlie

P.S. If you don;t already have it, you can get the 2000 RCSC Specification
as a free download from http://www.boltcouncil.org.


*
*   This email was sent to you via Structural Engineers
*   Association of Southern California (SEAOSC) server. To
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
*   send to the list is public domain and may be re-posted
*   without your permission. Make sure you visit our web
*   site at: http://www.seaint.org


* 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org