huangyhg

determining snow drift load in 1984
what was the predominant code used to determine snow drift in the '80's
the old nys code only says to include drift but not how to calculate it.
thanks

a familiar problem. my career didn't start until the 90's, but most of my time has been spent with the non-ibc based nys code. each of the different firms that i worked with using the old code calculated snow drift a different way.
the following way was the predominant way we calculated snow drift: because the code gave roof snow, we divided roof snow by .7 to get a ground snow load to be consistent with asce 7 and ansi a58. then we would take this derived ground snow load an plug it into the equations for drift height and snow density. there were many other engineers who did not take the roof snow load and divide by .7 to get a ground snow load. many used the roof snow load in the equations for snow density and drift height. i think that dividing the roof snow of the old code by .7 was the correct approach, because that's what the state did when they converted to the ibc. the drift loads were often huge because of how conservative the ny snow loads are.
before the u. s. codes starting giving procedures for drifted snow loads, engineers were essentially on their on. i have seen engineers ignore it or take a wild guess at it. we regularly refered to the canadian code which had provisions. if i recall the canadian provisions were pretty close to what we still use today.
most western states used ubc, eastern boca and southern, sbc, with others the nbc. wisconsin (from 1975 on) required a simple formula for snow drifting, which just last year switched over to ibc.
i hope this helps!
thanks for your input.
it seems the original engineer ignored the snow drift...
i'm not surpised by that. i have frequently found that snow drift was ignored in older buildings in ny, but this is not always the case. i am currently working on a building from 1980 that did unclude snow drift. good luck.

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