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Re: Diaphragms

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-----Original Message-----
From: Mark Baker <shake4bake(--nospam--at)>
To: seaoc <seaoc(--nospam--at)>
Date: Monday, August 18, 1997 3:33 PM
Subject: Diaphragms

>1. Do any of you use formula 31-1, section 1631.2.9 for calculating
>diaphragm load in single story buildings?
>2. When figuring diaphragm load do any of you use the weight of
>diaphragm + weight of walls tributary to diaphragm which are
>perpendicular to seismic load?
>3. When figuring diaphragm load do any of you use all four walls
>tributary to diaphragm?
>Consider this as my survey of the week :)
>Mark D. Baker
>Baker Engineering

I use the weight of the diaphragm + the tributary weight of the walls
perpendicular (normal) to the load. I disregard the end walls until I do the
shearwall analysis and then I take 0.183* the weight of the all and add it
in to the shear. Formula 31-1 would be used to distribute load into multiple
diaphragms in a mult-story builidng. I would assume (without actually having
run the numbers) that 31-1 would (or should) yield 0.75ZIwpx or 0.35ZIWpx -
depending upon the Rw that you choose.
I have also met an engineer online that considers the weight of interior
partitions into the lateral analysis for diaphragm and shear walls.
Theoretically, interior walls are not connected to the diaphrgm and
therefore would not contribute load into the diaprhragm, however I can't
fault him for taking a conservative approach - especially if he starts with
the assumption that the Rw is 8.

Dennis Wish PE