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Re: Alternatives to Post-Tensioning Construction

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To Nicholas Blackburn,

	Thank you for your informative response to my earlier writing on this
subject.  As Paul Feather wrote, it was very well stated, very well
stated indeed.

	Since receiving your response I have had the opportunity to view some
of the hardware which you have described first hand in an engineering
office.  It is very impressive when compared with similar hardware from
the 70s.  Never-the-less, it is in the office and not on the job site
where it would better serve.  And with the present market rejection it
will probably be some time before PT systems return to Calgary job
sites.

	Thank you again for your response.

				Best regards,


				H. Daryl Richardson

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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