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Re: Open Building with Gable using ASCE

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Paul Ransom wrote:

. > It would act a lot more like an airfoil if the underside was flat or
. > nearly flat relative to the exterior profile. Typically, with open gable
. > sheds, the interior roof is open with the same profile as the exterior
. > roof.

. > Also, the windward slope uplift is a result of wind blocked by a wall at
. > the windward face and forced with a vertical component past the eave.
. > This condition does not exist with an open structure so the transition
. > slope is different.

It is my understanding that an airfoil (uplift) is created by the wind flow 
over the top moving faster than the wind flow under the bottom.  Since there 
is nothing to force the underside wind up against the bottom of a gabled 
roof, the underside wind will travel an essentially level path.

It is also my understanding that the upward suction created by a vertical 
wall is the localized pressure at the eave, not the overall suction/pressure 
on a sloped roof.

It was described that the shed will be used to store equipment, therefore 
flow under the roof will be obstructed, adding to the uplift condition.

The ASCE wind tests at the Akron airship hanger showed where and how much 
wind pressure is changed by the slope of the surface (Ref: Grinter's "Design 
of Modern Steel Structures," Vol. 1, page 87.)

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

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