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RE: Bolt Tension

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Look at the losses that are typically experienced with prestressing strand 
due to elastic shortening, creep, temperature, etc., (20ksi - 35ksi).  All of 
these are a function of the concrete and environment, not the steel.  This 
should give you a good idea of what losses you might experience in tensioning 
the A449 anchor bolts.

One of the things that hindered development of prestressing was that the 
steels available at the turn of the century (the last century, not the 
upcoming one) did not have sufficient strength to provide residual stress 
after all losses.

Just one man's opinion.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

. > 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
. >