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Re: Alternatives to Post-Tensioning Construction

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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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