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RE: Re[2]: Pretensioning Of Anchor Bolts

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Rick,
Domed washers made of spring steel were specified under the pretensioned
anchor bolt nuts at the column bases for the Newark Airport Monorail
structures (see September 1998 issue of Modern Steel Construction:
http://www.modernsteel.com/ ).  Their use had been suggested by the Swiss
firm that did the original guideway design.  The use of pretension reduces
fatigue load on the anchor bolts and the domed washers help ensure that most
of the pretension was retained.  These washers are cupped and flatten out
under a given load.  The ones specified were made by the Rolex Company - a
single washer for a 1 1/2" diameter bolt would flatten fully at 20 kips, one
for a 2" bolt at 32 kips. Double washers were used to get double these
pretension loads (see note below).  One benefit of these washers is they act
like load indicator washers (you do not need to measure installation
torque).  I would use plate washer anchors at the bottom of such anchor
bolts and coat the upper shank so that they are free to elongate when
pretensioned.

Note:
If you turned the concave surfaces towards each other (or away from each
other) you load the washers in series and the total force to flatten two is
the same as one (the reaction from the top washer is the load on the bottom
washer). If you nest the washers so they are loaded in parallel (the load
required to flatten the top washer can be thought of as reacting through the
perimeter of the lower washer into the foundation with additional load
required to flatten the lower washer) you can double the prestensioning
force.

Ed Marshall, PE
Simons Engineering
Atlanta


> -----Original Message-----
> From:	Rick.Drake(--nospam--at)fluordaniel.com [SMTP:Rick.Drake(--nospam--at)fluordaniel.com]
> Sent:	Tuesday, October 27, 1998 11:15 AM
> To:	seaint(--nospam--at)seaint.org
> Subject:	Re[2]: Pretensioning Of Anchor Bolts
> 
>      As the person who started the thread on the pretensioning of anchor 
>      bolts, I have been very interested in all the comments, especially 
>      those by Harold and Charlie, who have grasped the reason for raising 
>      the issue in the first place.
>      
>      The petrochemical industry (and others) have used pretensioning of 
>      anchor bolts for many "nonbuilding" strcutures for years.  In fact in
> 
>      the recently published "Anchor Bolt Design For Petrochemical 
>      Facilities", 1997, ASCE uses 5 pages to talk about pretensioning of 
>      anchor bolt procedures, including applications, methods, and 
>      tightening sequences.  That is why I was curious about another 
>      reputable engineering organization, AISC recommending against it in 
>      the LRFD Commentary.
>      
>      As a member of both AISC and ASCE (as well as SEAOSC and EERI), I am 
>      trying to resolve the conflicting viewpoints.
>      
>      Rick Drake, SE
>      Fluor Daniel, Inc.
>      Member ASCE, AISC, EERI, SEAOSC
> 
>