Response to a reader question regarding using the NSCP for estimating wind loads on irregular shapes

A reader asked:
How would you evaluate the pressure coefficients for structures with irregular polygon shapes. An example would be those structures with a plan shape resembling the letters "W" or "K." Most of the pressure coefficients in the code are for uniform cross-sections such as circle, rectangle, square, and so on. I have my own approach on this (mostly based on engineering judgement), but I would like to hear first on a wind load aficionado, such as yourself.
Aficionado = sigh. Anyway, he is right, codes usually do not provide for such rather uncommonly used building shapes. You can of course use engineering judgment based on the coefficients for shapes given in the code, which are based on wind tunnel tests on those specific "regular" shapes. That said, the more accurate and most rational method is to use the wind tunnel approach (i.e. Method 3 in NSCP 2010, or ASCE7). Unless it is a shape that has been tested before and is published in literature, you might not be accounting for unexpected wind flow patterns that could increase wind pressures at specific locations, or you might not be realizing cost savings by using a more accurate approach. If you are dealing with tall buildings, it is easy to justify the relative low cost of doing a wind tunnel test.

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