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Re: Alternatives to Post-Tensioning Construction

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Daryl ,

Use bonded post-tensioning tendons.

At 11:23 AM 9/05/01 -0600, you wrote:
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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Regards  Gil Brock
Prestressed Concrete Design Consultants Pty. Ltd.
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