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Re: How Can Force in "All Thread" be Det

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The strand chucks that I have specified are as you described.  And, yes, they 
rely on wedges to grip the strand.  However, the wedges in the strand chuck 
are contained within the chuck and held in place with a spring and removable 
cap.  The wedges that were supplied by the P/T supplier on the first GLB 
prestressing that I did were loose, and had to be hand-placed in the 
supplier's donut with great difficulty.  (Bear in mind that this advice to 
not use "wedges" was given to me in about 1985, so I don't recall the exact 
words.  I do, however, recall the results of not carefully following that 

The P/S strand that I specified is A 416, Grade 270, Low Relaxation, and the
threaded rods that I specified were to conform to A 36.

The steel sub-contractor has not yet specified exactly what he proposes to 
use as a substitute for the P/S strand except that he wants to use "all 
thread."  Once "we" find an acceptable method of measuring the force in "all 
thread" and he submits the exact material that he proposes to use, I will 
review it carefully and keep in mind many of the things that have been 
brought to my attention on this list.

Thanks very much for your contribution to my query.

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

GSKWY(--nospam--at) wrote:

. > Out of curiosity,  what are you calling a strand chuck?  As in the 
. > statement below:

. > >  "Use strand chucks to anchor the strands --- don't use wedges."  
. > Strand chucks are multi-use chucks (with wedges) that are used to anchor 
. > pre-tensioning strand against the bulkheads.   They are also used to do 
. > things like pull out strand in repairs, to anchor strand for testing, 
. > etc.  About the only way to anchor a strand without using wedges is a 
. > compression fitting, also referred to as a mechanically attached anchor 
. > or a swedge.

. > You also should probably be clear on what you are specifying and/or the 
. > contractor is proposing for bar.  Williams `All-Thread-Bar' is in fact a 
. > 150 ksi prestressing bar,  so is the Dywidag `Threadbar'.   

. > Note also that prestressing bar (ASTM A722) is not low-relaxation,  it is 
. > stress-relieved.  The relaxation is much higher than low-relaxation 
. > strand.  If the bars are stressed to 0.8fpu,  0.6fpu is tyipcally used as 
. > the final effective stress in concrete   I think it would be lower when 
. > prestressing wood though.

and added:

. > Another thought:

. > Use Dywidag bars.  I have used them on permanent tieback applications w/ 
. > the tension close to 0.6Fy.  There is a special rig that turns the nut and
. > stresses the bar.  I don't recall exactly how the rig works to give you a
. > tension force.

. > Don Carroll

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