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Re: Alternatives to Post-Tensioning Construction

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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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