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RE: Subject: Calculations of Base Shear

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I agree with Mark's approach. I usually use the full wall weights in the
diaphragm design for simplification; but I recently separated the parallel
and perpendicular wall weights according to seismic direction for a design
with tall, fully grouted 12-inch masonry walls. In any case, the total
weight of walls must be accounted for in calculating total base shear. 

William C. Sherman, PE
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)

> -----Original Message-----
> From: Mark Gilligan [mailto:MarkKGilligan(--nospam--at)]
> Sent: Monday, February 24, 2003 3:10 PM
> To: seaint(--nospam--at)
> Subject: Subject: Calculations of Base Shear
> Bobby
> There are two approaches:
> In both approaches you must consider all building weight above that is
> tributary to the level above the found floor when calculating 
> the total
> base shear.
> When distributing the forces to the shear walls you can 
> ignore the weight
> of the shear walls at that level when the shear walls are 
> parallel to the
> direction of the earthquake motion.  This ignored weight 
> times the proper
> coefficient should then be applied directly to the shear 
> wall.   This can
> be worthwhile if you have a particularly heavy wall or when 
> you want the
> absolute minimum force in the diaphragm.  This is more 
> difficult when you
> are using a computer program to analyze the structure as 
> opposed to a hand
> analysis.
> The more common approach is to assume all of the wall weight 
> tributary to
> the diaphragm is lumped together.  This is quickier and less prone to
> mistakes. 
> Mark Gilligan

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