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# Internal Wind Pressure for Partially Enc

• To: seaint(--nospam--at)seaint.org
• Subject: Internal Wind Pressure for Partially Enc
• From: Roger Turk <73527.1356(--nospam--at)compuserve.com>
• Date: Wed, 19 Nov 2003 16:37:48 -0500

```Rich,

Your rear wall is both a windward wall and a lee wall so you would add the
windward wall pressure and the lee wall suction.  From ASCE Transactions,
Part II, Volume 126, 1961, page 1156, Table 4(b), (I) One long wall open,
shows a building just as you describe it.  The inside pressure coefficient is
0.8, and the external suction coefficient is -0.5.

The figure in the table is for a roof slope of 30 deg., however, assuming
that the internal pressure and external suction for the leeward roof would
be the same for a windward low slope roof, the internal pressure coefficient
is 0.8 and the external suction coefficient is -0.4.  However, if the wind is
skewed 45 deg., the internal pressure coefficient on the roof is 0.7, but the
external suction coefficient is now -0.7.

HTH

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Rich Lewis wrote:

. > I am designing a steel framed shed that is 40'x60'.  One side is open on
. > the 60' length.  The other 60' wall is sheathed as well as the two 40'
. > side walls.  It is obviously a partially enclosed building.  ASCE 7-95
. > has an internal pressure coefficient of +0.8 and -0.3.  A windward wall
. > coefficient Cp is also 0.8.  My question has to do whether these are
. > additive.  If I have wind blowing on the open face it passes through
. > until it hits the back wall.  There it is windward and has a 0.8
. > coefficient.  This means the windward pressure coefficient is 0.8.  If I
. > add an internal pressure coefficient then this must be equal and opposite
. > in nature and not only presses against the back wall and uplifts the roof
. > but then blows back out the front of the buildingwhere there is no wall,
. > therefore negating the windward pressure.  So it seems to me the correct
. > way to do this is to say the inside pressure and the windward pressure
. > are one in the same.  It does put uplift pressure on the underside of the
. > roof which is additive to the top side uplift, but doesn't add extra
. > pressure in the horizontal direction.

. > Am I looking at this correctly?

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