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Re: Snow Drift Load

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Wontae Kim,

        The French have no monopoly on this system of building support.
My first exposure to the system came in about 1973 when I reviewed a
Russian made documentary regarding construction on permafrost in The
Soviet Union for a class I was teaching.  The reason that the Russians
were using this system was to prevent heat from the buildings from melting
the permafrost and, hence, destroying the foundation integrity.

        About three years after that I was involved as Lead
Civil/Structural Engineer on a major gas development project in the
Canadian Arctic (on the north coast "just off the beach," we used to refer
to it).  We investigated many elaborate schemes for protecting permafrost
and, in virtually every case, setting the buildings high up on piles was a
fundamental part of the scheme.

        The primary question became not whether we would set the buildings
on piles but "how high?"

        The western Arctic doesn't get a lot of snow, only several inches
to a foot or more.  It does, however, get a lot of wind and there are no
trees or other natural obstacles to provide shelter so gigantic snow
drifts are the norm wherever buildings or other obstacles are
constructed.  It was important to maintain free air flow under the
buildings; therefore, it was deemed important (by others, not by me; I was
one of the sceptics) to conduct a model study to assess the extent of snow
drifting and the interaction between the drifts and our raised buildings.

        We got a lot of useful results specific to our project plus I
developed a much more open mind regarding snow drifts and the extent to
which they could occur; I was no longer a sceptic.

        Let me try to describe at least some of the results of the study
that I think may be of use to you as I remember them.  Keep in mind that
a) all this was about 30 years ago and my memory is probably less than
perfect; b) my former employer is very secretive; and c) the original
client is secretive to the point of paranoia.  In my opinion there is no
possibility that they would agree to release or even sell you the complete
information.  Furthermore, nothing was ever built; the project was
cancelled; it turned out to be nothing more than a two year research
project involving about a hundred people!

1.    The site was a river delta about 5 feet above mean sea level. there
were no trees or other obstacles to wind for miles in any direction.

2.    The buildings containing all equipment were to be build off site and
transported by barge to the site where they were to be off loaded by
special transporters and and set on the pre constructed pile foundations.
The building module sizes were restricted to 50' by 100' by about 80' or
90' tall.  For reasons of fire safety the modules were well separated but
interconnected by enclosed walkways.

3.    For studies with the buildings flat on the ground (no raised piles)
snow drifts maxed out at about 30' and were tight against the building.
It would be extremely difficult to enter or exit the building through
doors OR windows and there would be NO airflow under the buildings.

4.    For studies with the buildings 4" above ground snow drifts maxed out
at about 25' but were 4' to 6' clear of the buildings.  Entering or
exiting the buildings was no problem but air flow under the buildings not
sufficient to maintain the permafrost in a frozen state.

5.  For studies with the buildings 8' above ground snow drifts maxed out
at about 20' and were back 10' or 15' from the buildings.  Exits were well
clear of snow and airflow under the buildings was adequate.

6.    As I recall we did study higher placements but the results did not
improve significantly.  Both the types of transporters available and the
snow drift study indicated that our optimum height would be about 8' above
grade.

7.    Snow drift slopes (and this is just a guess) would be about 20 to 30
degrees from the horizontal for the side of the drift away from the
building and (+-) 60 degrees from the horizontal on the side of the drift
facing the building.  I would expect the ground near the building to be
clear of snow for a distance of  1 to 1.5 times the elevation of the
building above grade if air may pass freely under the billing.

8.    I have no idea how high your drifts could be.  This would depend on
the amount of snow available and the geometry of your structures. You may
consider doing your own model study to find this out if you really need
it.  Our site had 500 square miles of unobstructed snow in any direction
but but there was still a limit to the height of drift that could occur.
The amount of snow may be limited for your drifts.  Perhaps 10' or 12'
would be your maximum drift and even that might be improbable; but it is
possible for it to be a lot worse.

        I hope this major dissertation is of some help to you.

Regards,

H. Daryl Richardson

Wontae Kim wrote:

> About Snow Drift Load:
> If a building has pilotis on the ground level, which means this
> building is separated from the ground using columns, how should I
> consider snow drift load on the ground level?
> Is there triangular shape surcharge snow drift?
> If there is, what shape of triangle?
> (How wide its bottom W is?)
> In my opinion, there is no snow drift for the turbulent wind effect?
> May I hear your opinions?
>
> ("Piloti" is a French term for a series of columns which support a
> building above an open ground level. Villa Savoye, constructed in 1928
> by Le Corbusier, is a classic example of their use)
>
> ****Wontae Kim****
>
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