Pressure Coefficient for Cladding (Wind Load - National Building Code of Canada)

[StrucPEng]

I am working on analyzing windows in a low rise structure in Canada. My building meets all the requirements of the National Building Code of Canada wind loading code to use the combined CpCg values determined in figure I-8 of the commentary (Fig. 4.1.7.6-B of NBCC). My question arises in using the graph to determine the coefficients. The X axis of the graph is "Tributary Area" and I am not able to determine if it is the Tributary area of the section denoted by "e" or "w" or is it the tributary area of the element I am interested in, namely the area of the window in the "e" or "w" region of the building. This obviously makes a difference as my end section tributary area is ~50 sq. meters but my window is ~5 sq. meters.

I have attempted to look up worked examples but it appears that the tributary area decision is not a really well defined quantity and some examples will use 1 sq. meter to be conservative which i can do but want to avoid if possible.

Lastly, I know this this is very specific to the NBCC and the noted figures, for the Americans this is similar to Figure 30.4-1 of the ASCE 7 code.

Thanks for the help!

 

[jayrod12]

It's the tribe area of the thing you are designing. If you're designing glass is the tribe area of the glass lite you have. I generally just defer to 1m^2 unless it's a girt or column supporting a significant area.

 

[StrucPEng]

So the area of the element that falls in the "e" or "w" region. Thanks Jayrod. I would like if they made that explicitly clear, but maybe its just my bad interpretation of it.

 

[jayrod12]

Oh no, you aren't the only one confused.

Check out jabacus.com. It will do the dinky little calcs for you and is more precise than reading it off a chart.

 

[StrucPEng]

Wow, that site is pretty great, took about 10 seconds to get the values I spent the last hour working out in MathCAD. Thanks for the info Jayrod.