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RE: base plates subject to uplift

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Paul,

I've been there and solved that issue.  Hardened washers are not effective
in transferring large tension forces in an oversized hole.  I have pictures
to illustrate this one.  Go ahead and use the oversized hole in the base
plate, use a 1/4" or 3/8" plate washer with the standard oversized (plus
1/16") hole in the plate washer.  If you are using an F 1554, 105 ksi anchor
bolt with preload, use a standard hardened washer on top of the plate
washer.

Also specify a gage metal setting template supplied by the structural steel
fabricator.  I even require the grids and north arrow to be put on with a
paint stick by the fabricator.  It is one less place to have a screw up.
The fabricator has to provide the anchor bolt setting plan and the anchor
bolts, the setting template is a natural, tiny extension.  On large projects
with big name fabricators, this has been routine for years.  

When I see wood setting templates fabricated by a carpenter, 9 times out of
8 there will be a mistake.  The superintendent hands the plans to a foreman,
the foreman draws paper sketches of the templates and gives them to a
carpenter, the carpenter makes the templates out of scrap plywood from the
sketches, the carpenter gives the plywood templates to the laborer, the
laborer leaves the plywood templates in the rain for as long as possible,
and truck tires routinely use the templates for traction.  The engineer
prays that the anchor bolts are in the right county with tolerance measured
in latitude and longitude.  This system is nuts!!!

Regarding preload.  How many of us would ever not preload a seismic frame
bolt that is in tension, yet that is the routine for anchor bolts.  Here we
have the connection that makes the entire frame work putting cyclic seismic
load in an anchor bolt that has a notch effect due to the net tension area
reduction at the threads.  I like to preload the anchor bolts.  By the way,
that is routine in tank structures, and high seismic structures that I work
on.

Regards,
Harold Sprague


> -----Original Message-----
> From:	PFFEI(--nospam--at)aol.com [SMTP:PFFEI(--nospam--at)aol.com]
> Sent:	Friday, June 16, 2000 1:41 PM
> To:	seaint(--nospam--at)seaint.org
> Subject:	base plates subject to uplift
> 
> What is the maximum oversize bolt hole diameter for a base plate subject
> to 
> uplift? AISC allows 1-5/16" diameter holes for a 3/4" diameter bolt.  This
> is 
> larger than the dimension  across the flat of  a 3/4" diameter bolt of 
> 1-1/8", and would seem to have a significant impact on the capacity of the
> 
> connection.  Limiting hole diameter to 1/16" oversize seems overly 
> restrictive for field fit up with anchor bolts.  How effective are
> hardened 
> washers to transfer upfilt forces?
> Thanks 
> Paul Franceschi, S.E.
>