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RE: Post-tensioned slab on grade

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Dick,

As the expression says, "Been there, done that".  Unbonded PT should raise
warning flags, but it can be done safely and effectively by an experienced
crew.

I also had to do the forensic analysis on some PT construction that went
wrong.  One parking garage constructed in the mid 1970's (one of the first
in the US), unbonded greased kraft paper, design problems, pulls that were
too long, construction problems, erupted strands, angry owner, etc.  This
was the OSHA poster child that resulted in the warning that construction
workers were not to stand behind the jacks while tensioning the strand.  The
jacks reportedly jumped off the anchors about 3 feet.  The strand was not as
unbonded as it was supposed to be.  The repairs were about $750,000 in 1992,
well short of the 50 year life expectancy. One cut strand during a previous
repair launched a strand through the precast spandrel, and kept going for
about a block.

I was also consulted on a delaminate slab that almost killed the inspecting
engineer.  It delaminated at a corner during inspection.  Resulted in
revised anchorage designs.

After seeing all of the problems, I have become a fan of the bonded
encapsulated systems (corrugated plastic sheaths grouted after tensioning).


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


-----Original Message-----
From: Horning, Dick/CVO [mailto:dhorning(--nospam--at)CH2M.com]
Sent: Thursday, November 05, 1998 10:24 AM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: Post-tensioned slab on grade


Sounds like the voice of someone who's had to do this before.

	-----Original Message-----
	From:	Harold Sprague [SMTP:harold.sprague(--nospam--at)neenan.com]
	Sent:	Thursday, November 05, 1998 8:47 AM
	To:	'seaint(--nospam--at)seaint.org'
	Subject:	RE: Post-tensioned slab on grade

	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