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Re: Post-tensioned slab on grade

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Thanks to everyone for yourkind advice !

I forgot to mention that the strand is sheated in smooth plastic pipe ,
and grouted after tensioning. It is not a true bonded type , neither an
unbonded type. There is no way to detension the strand from the bearing
plates , as the projecting length is too short to allow gripping by any
jack or chuck barrel assembly.


Juan C. Gray 

Harold Sprague wrote:
> 
> 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
>