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RE: Bolt Tension

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Ed

Hope I am wrong but it seams to me the total force needed to flatten two
domed washers would be the same as the force to flatten one domed washer.
Two springs in a series have an equivalent stiffness of one half the
stiffness of one spring. As you moved the nut through twice the distance you
still only got the force of one domed washer. If you see this differently or
the manufacture or testing lab indicated you can double up on the washers
and get twice the force let me know.

Acie Chance

> ----------
> From: 	Ed Marshall[SMTP:elmarshall(--nospam--at)HASimons.com]
> Sent: 	Thursday, April 30, 1998 12:28 PM
> To: 	'seaoc(--nospam--at)seaoc.org'
> Subject: 	RE: Bolt Tension
> Importance: 	High
> 
> We have used domed washers made of spring steel under pretensioned
> anchor bolt nuts to help ensure that most of the pretension was
> retained.  These washers are cupped and flatten out under a given load.
> The ones we 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.  We used double washers to get double these pretension
> loads.  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.
> 
> Ed Marshall, PE
> Simons Engineering
> Atlanta
> 
> > -----Original Message-----
> > From:	Paul McEntee [SMTP:pmcentee(--nospam--at)home.com]
> > Sent:	Thursday, April 30, 1998 1:30 AM
> > To:	seaoc(--nospam--at)seaoc.org
> > Subject:	RE: Bolt Tension
> > 
> > While were on te subject of bolt tensioning...
> > 
> > We were having this debate over whether or not to tension high
> > strength threaded rods in a fixed base connection for a moment frame.
> > Some argue that you must tension the bolts, otherwise you'll get large
> > rotations of the base plate before it starts taking moment.  Others
> > were of the opinion that pre-tensioning the rods loads the concrete,
> > causes it to creep, and the bolt tension will relax anyway.  I'm kind
> > of with the creepy group myself (couldn't resist).  The issue of it
> > being difficult and expensive to tension the rods came up.  In one
> > particular case, our detail calls for 1.25" diameter A449 Rods
> > tensioned to 48 kips, and we are now in the process of getting the
> > inspection company to take samples of the rods into their lab (rods
> > are too big and too strong to use a skidmore on site) to measure the
> > torque required to get that tension using the contractors wrench.  I
> > don't sympathize with the difficulties this causes the contractor too
> > much if the pre-tensioning of the bolts truly increases the fixity of
> > the connection, but if the tension is going to relax in a few months
> > anyway, I'd hate to have the owner paying extra for this.  Not to
> > mention the fact that there is a risk of breaking the bolts while
> > doing this.
> > 
> > Appreciate any fresh (ie, not from my coworkers) opinions on this.
> > 
> > Paul
> > 
> > A self proclaimed lurker
> 
> 
>