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# Internal Wind Pressure for Partially Enclosed Bldg.

• To: seaint(--nospam--at)seaint.org
• Subject: Internal Wind Pressure for Partially Enclosed Bldg.
• From: richard lewis <rlewistx(--nospam--at)juno.com>
• Date: Wed, 19 Nov 2003 14:29:03 -0600

```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?

Thanks.

Rich

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