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Re: Alternatives to Post-Tensioning Construction

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www.post-tensioning.com


----- Original Message -----
From: "Juan C. Gray" <juangray(--nospam--at)col2.telecom.com.co>
To: <seaint(--nospam--at)seaint.org>
Sent: Thursday, May 17, 2001 8:33 PM
Subject: Re: Alternatives to Post-Tensioning Construction


> Do you by any chance have the web address for PT-Data?
>
> Juan C. Gray
>
> Paul Feather wrote:
> >
> > Nicholas,
> >
> > I could not have stated it better.  As far as the software is concerned
we
> > use PT-Data typically (Always current version), have older versions of
ADAPT
> > and are looking closely at upgrading soon.
> >
> > Paul Feather
> >
> > ----- Original Message -----
> > From: "Nicholas Blackburn" <nblackburn(--nospam--at)fdgoak.com>
> > To: <seaint(--nospam--at)seaint.org>
> > Sent: Wednesday, May 09, 2001 11:57 AM
> > Subject: RE: Alternatives to Post-Tensioning Construction
> >
> > > Post tensioning systems have come a long way since the 70's.  A
typical
> > > modern system includes complete factory-encasement of the strands in a
> > > waterproof grease and then an extruded plastic sheath and either of
the
> > two
> > > main types of anchorage available:
> > >
> > > 1) standard anchors which are bare castings and provide minimum
protection
> > > to the gripper zone and the transition between the anchor and the
strand.
> > >
> > > 2) fully encapsulated, electrically isolated anchors that are
completely
> > > covered in a thick plastic coat, have a grease cap over the gripper
pocket
> > > and a plastic trumpet that fully engages and seals the strand
sheathing to
> > > the anchor sheathing.
> > >
> > > A properly detailed PT system will provide excellent performance over
the
> > > life span of the structure.  In areas where salt exposure is a problem
the
> > > typical system recommended is the fully encapsulated one.  Further
> > > protection can be provided with proper specification of low-shrinkage,
> > > high-density concrete containing fly ash and/or silica fume.
> > >
> > > The durability of any concrete structure, PT reinforced or otherwise,
is
> > > predicated on proper and timely maintenance coupled with good
detailing
> > and
> > > construction practices.  The reasons previously stated by others on
the
> > list
> > > note the benefits of PT.  I would however try to locate penetrations
early
> > > on in the design process and only locate conduit parallel with and in
the
> > > slab. Plumbing should be kept out of the decks for maintenance reasons
if
> > > nothing else.
> > >
> > >
> > > Nicholas Blackburn, PE
> > >
> > > ps: On a related note what software does the List use for PT design.
We
> > use
> > > PT Data typically but I am familiar with Floor and ADAPT PT.
> > >
> > > -----Original Message-----
> > > From: h.d.richardson(--nospam--at)home.com [mailto:h.d.richardson(--nospam--at)home.com]
> > > Sent: Wednesday, May 09, 2001 10:23 AM
> > > To: seaint(--nospam--at)seaint.org
> > > Subject: Re: Alternatives to Post-Tensioning Construction
> > >
> > >
> > > Fellow engineers,
> > >
> > > I am astonished by what I am reading!
> > >
> > > In Calgary during the late 1970s, up to 1981, most residential and
> > > office buildings being built were of post-tensioning construction.
> > > There were literally a few hundred of them built.  Serious structural
> > > problems have since developed with these buildings.  Breaking of the
> > > cables as a result of corrosion/oxidation is the culprit.  Water
> > > infiltration of the system seems to be a major contributing factor.
> > >
> > > Fortunately for me, during that period of time I was working for
> > > Fluor
> > > and similar employers, hence, I have no personal involvement in the
> > > problem at the design stage.
> > >
> > > Presently, there are engineers doing a good "bread and butter"
> > > business
> > > doing annual structural inspections locating broken cables; and there
> > > are contractors specializing in replacing broken cables.  It's a lot
> > > like replacing light bulbs or, as one mechanic I used to know years
ago
> > > would say "like fixing Fords".  It's difficult to sell a
post-tensioned
> > > building in Calgary at the present time; most buyers are aware of the
> > > high cost of maintaining the structure.  I doubt if there has been a
> > > post-tensioned building built in Calgary in the last 20 years.
> > >
> > > I am curious to know how the corrosion problem is being dealt with
> > > in
> > > other locations at the present time.  Moisture infiltration has to be
a
> > > problem, especially in coastal climates like Seattle.  I hope the
thread
> > > of the present discussion will extend to that topic.
> > >
> > > Regards to all
> > >
> > >
> > > H. Daryl Richardson
> > >
> > > Paul Crocker wrote:
> > > >
> > > > Of the several dozen residential project I am aware of having been
done
> > in
> > > > the last few years in the Seattle area, any that were too tall to be
> > wood
> > > > were P.T. flat plates.  P.T. typically allows a shallower floor
system
> > > than
> > > > steel framing or mild steel slabs.  The P.T. also tends to reduce
> > > deflection
> > > > problems that can occur in mild steel slabs.  Ducts and conduits can
be
> > > > burried in the slab, which is an advantage overall even if it is not
> > > > something I enjoy as an engineer.  Openings are not very hard to
deal
> > with
> > > > if placed *before* the slab is poured.  It becomes more difficult to
> > place
> > > > openings afterwards, however, as it is not a great idea to hit
cables,
> > > > although a few will get broken by careless plumbers from time to
time.
> > > Jobs
> > > > that anticipate cutting a large number of openings in the slab
> > throughout
> > > > the building's life are typically not P.T.
> > > >
> > > > Paul Crocker, P.E.
> > >
> >
>
>
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