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RE: Snow Load + Seismic

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-----Original Message-----
From: Reza Dashti Asl [mailto:rezadashti(--nospam--at)] 
Sent: Tuesday, July 25, 2006 12:31 PM
To: seaint(--nospam--at)
Subject: Re: Snow Load + Seismic

So the question is what percentage of the mass can move freely and 
how much of it will rest on the structure to add to the W.

-----/Original Message/-----

I think that snow on the roof has got to be considered an active mass
for seismic analysis. It just seems to me that the calculation of the
roof snow load defined by the code(s) takes into account the probability
of its presence, and therefore what would need to be accounted for would
be the probability of its presence in a seismic event.

Thirty-three percent might be too simplistic--but I keep going back to
the idea that you've already accounted for all the other probabilities,
except perhaps a "risk/importance factor" (i.e. by how much does the
danger of exceeding the allowable response increase if you DO happen to
hit on a seismic event with lots of lovely wet stuff on top of your

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