Wind on a U-Shaped Building

[phamENG]

A search of the forum and the internet in general failed to provide a very good answer, so hopefully somebody here has a good reference. I'm designing a 5 story, u-shaped building. Overall dimensions are about 180ftx180ft with a 60' "thickness" - pretty standard apartment building. Standard, that is, so long as you're not looking at ASCE 7-10. It sadly falls outside of the realm of regularly shaped buildings and into the need for "approved literature" or "wind tunnel testing." Well I can tell you we can't afford to rent the local wind tunnel, so I'm hoping for some good literature to apply. My gut tells me that the orthogonal wind loads should be roughly those calculated for a rectangular building (a slight increase when considering the sides of the U, and perhaps a bit of eccentricity from the unbalanced internal pressures in the courtyard), but a quartering wind has me concerned. A side note, this is on the east coast and wind will more than likely control most of the lateral design (with the possible exception of an amplified collector load on the first floor here or there).

I found this presentation from NCSEA, but the resolution is bad and I can't find it replicated anywhere with the actual explanations that were probably given by the presenter.

Thanks for any help you can provide.

 

[racookpe1978]

Hmmmn.

Seems like a quartering wind would have less pressure (over the whole wall + wings structure) than any other direction.

You have a natural bracing effect of the two wings of the U adding stiffness, regardless of wind direction - except for the single case of the U catching the wind dead in. And, even then, then two wings add a bracing coefficient not seen on a tall, wide, skinny single surface perpendicular to the wind..

 

[phamENG]

I should also mention that this is a wood building (the first floor is....interesting). Therefore, the diaphragms are flexible. I agree the wings will give me lots of bracing, but right now I'm concerned with load analysis based on the irregular geometry so I can figure out just what load to put into those shear walls. The quartering wind is somewhat less, but it also introduces an additional torsional load on the overall structure. It's easy to determine for a regular building, but I'm hoping to find some well respected guidance on application of those eccentricities for this shape (a modification to ASCE 7-10, Figure 27.4-8, for example). Thanks for the input, though.

 

[WARose]

You probably wouldn't get anything dramatically different than the code (i.e. a coefficient of about "2"). Attached is the a reference from Canada that contains some wind coefficients based on testing. When you think about it, what you are describing is kind of like a scaled version of an ordinary steel shape (not considering any dynamic effects).

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1527018235/tips/HandbookOfPressureCoefficientsForWindLoads_1965_oatalu.pdf[/url]

 

[SAIL3]

It is an opportunity to use some engineering judgement. At first glance, there are two wind conditions that could give the highest overall wind loads on portions of the bldg...

A/..wind directly into the U-shape(say North)..what overall drag coeff to use?...WaRose's suggestion of using "2" and comparing it to a scaled-up steel shape is a good place to start...absence any testing data, I might consider using "2.5" at least for the inner portion of the U....the difficult part is what Cp to use locally for cladding etc....if I use 0.6 for the leeward, then I have 2.5-0.6= 1.9 for the windward on the inside of the U....

B/...South wind.....0.8 windward....2.5-0.8 = 1.7 leeward on inside of U.....

C/...quartering wind...keep it simple......0.707NS + 0.707EW...etc

The portion that would require my greatest attention is on the inside of the U..call it a courtyard, where wind from the North gets trapped resulting in high turbulence and wind from the South causing high suction/separation...

above is just a first cut at this...when I have no test data and have an unusual case, I have no qualms in going conservative....

A sketch would help in getting more informed input

 

[dik]

Attached is the a reference from Canada

The data was based on Swiss Engineering data predating it by 20 years.

Dik

 

[WARose]

The data was based on Swiss Engineering data predating it by 20 years.

And? It has shapes in it that ASCE still doesn't.

 

[TLHS]

When you're firing wind into the U, it seems like it would be pretty comparable to the case where you have internal pressures from a large door opening. That might be somewhere to start for literature.