ASCE 7 Design wind pressures to wind load used in MWFRS design

[bdub97103]

Hi,

Im having a difficult time understanding how you convert ASCE 7 design wind pressures to just 1 design wind pressure, that is shown in most textbook/examples. When you use ASCE 7 (chapter 28 in my case) you end up with a table of design wind pressures that vary. But when you look through all the MWFRS examples, they just give you one wind load value. Do you guys have any recommendations on where I can learn about how to go from ASCE 7 design pressures to actual apploed loads on my building?

For example, on one face of a building you're given wind pressures 1 & 1E, then on the opposite face, you have wind pressures 4 & 4E. How am I supposed to convert those to one pressure? Is that specified in the code somewhere or is there a textbook that I can read this in?

Thanks!

 

[driftLimiter]

I don't think your supposed to convert them to one pressure. I would suggest that the textbook example is too simplified. If I have end zones regions of the diaphragm with higher wind loads, I model them as such and calculate the peak shear and moment in the diaphragm based on a beam model with more than one distributed load magnitude on it.

Someone might be able to work out the relationship between end zone pressure, building width, and peak bending moment/shear of diaphragm and come up with a nifty conversion to a single uniform pressure. But I haven't seen this done much in practice.

There are other wind methods in ASCE that use consistent pressure magnitudes across the building that would result in a diaphragm load diagram like the one in the textbook.

 

[milkshakelake]

I think that example is just showing the basic idea of how a diaphragm is loaded, and not the real wind load. I would apply the ASCE 7 loads.

In my area (New York City), the building code allows you to use uniform 20 psf (times exposure factor) up to a certain height of building, and higher uniform psf up to another height. I haven't seen that anywhere else. I still do the more complicated ASCE 7 calculation because I have so many spreadsheets set up that way, and the software I use (ETABS) also does the full ASCE 7 calculation. About driftLimiter's point about a conversion to a single uniform pressure, the building code value of 20 psf ends up being very close to the real value most of the time for 98 MPH wind (ASD ASCE 7-05, not the new code; we're stuck in the past here). Your mileage may vary.

 

[JedClampett]

If you're trying to convert all the wind pressures into one case, you might be making a unconservative mistake. I doubt you'll have a problem, but Bill LeMessurier had a bit of an issue with the Citicorp Center. And he checked at least two cases, just not the diagonal ones.

 

[Whiffle404]

Alam Williams' book Seismic and Wind Forces provides easy to follow examples of what you're looking for:

https://www.amazon.com/Seismic-Forces-Structural-Design-Examples/dp/1609833961