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RE: Post-tensioned slab on grade

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Byron,

I have not come across a maximum elongation limitation. This is one of those
things that you need an experienced guy on the torch.  A torch can cut or it
can add heat.  

You can calculate the elongation due to the stress in the strand and the
length.  This is important for the older PT, because you might not have
totally relieved the tension when you see X inches of strand go back into
the sheath.

On the newer systems the heat needs to be applied over a length of strand to
provide as long an area as possible for the elongation to occur.  At the
same time you do not want any of the heated strand to be in the section that
must be retensioned.

In addition to Structural Preservation Systems, Inc. as suggested by Roger
Turk, some other suggested contractors are:
VSL 408-866-677 
PostTech Construction Technologies 416-490-0575
Tech Research 612-292-9638

Regards,
Harold Sprague, P.E.
The Neenan Company
harold.sprague(--nospam--at)neenan.com


-----Original Message-----
From: Byron Benson [mailto:bbenson(--nospam--at)uzuncase.com]
Sent: Thursday, November 05, 1998 11:06 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Post-tensioned slab on grade



Yes, it does sound like the voice of experience.  Harold, have you
encountered a maximum elongation for which heating the strand is still an
effective and safe way of relieving the stress?
Byron


>If it is unbonded. (Which it probably is)
>1.  Chip out a window exposing the strand.
>2.  Heat the strand in the middle to relieve the tension.
>3.  Cut the strand after the stress is relieved.
>4.  Re-tension and re-anchor the strand at the edge of the new opening.
>5.  Dress out the cut at the perimeter.
>
>Harold Sprague
>The Neenan Company
>harold.sprague(--nospam--at)neenan.com