Does wind uplift occur along the long axis?

EngineerofSteel · Jun 13, 2005

I rethink this often. When wind hits the facade of a gabled roof building, and flows along the ridge line, parallel to it (the Z direction, lets say), the wind is not really taking a longer route. So, since uplift occurs from the Bernoulli effect, is wind uplift calculated equal to wind in the X direction (perpendicular to the ridge line)?

My gut tells me the uplift force is reduced. How are others calculating uplift in the Z axis, if at all?

Also, when using "equivalent lateral pressure" to calculate the seismic force, is there an uplift component? I'm considering that a seismic ripple has both a horizontal and vertical component.

Thanks for any & all info.

Dairy Designer, California

JAE · Jun 14, 2005

Much of the roof wind uplift is due to the upward flow of air when it hits the windward face of the building. The upward pressure is higher in the near-zone areas of the windward roof and may diminish toward the leeward sides, but this is not always true. So with a gable roof, the uplift is somewhat independent of the ridge configuration - both have windward walls.

EngineerofSteel · Jun 17, 2005

Thanks, JAE, for the response. I think I read an online article which attributed uplift to the accelerated air passing over the roof. The redirected air coming from the face can push on the eves, I see that.

Also, I found in the 97 UBC that the uplift component of the seismic wave is neglected is ASD. For Strength Design, it is calculated, and the equation is in 1630.1.1

I thought I'd include that for anyone searching for that answer.
-Dairy Designer

unclesyd · Jun 18, 2005

Here is a software program/demo (Archon Win 98) that calculates the wind pressure on buildings.

They have several other programs that I use regularly.

http://www.archoneng.com/

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Does wind uplift occur along the long axis?

EngineerofSteel

Structural

JAE

Structural

EngineerofSteel

Structural

unclesyd

Materials

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