currently analyzing. Then divide by the moment arm and subtract the
appropriate portion of dead load (60%) to obtain my uplift load. Gets pretty
high on three story buildings on the West coast. I have seen other engineers
ignore the laws of statics and nature and often wonder what will happen to
their designs.
Mark E. Deardorff, SE
R & S Tavares Associates, Inc
9815 Carroll Canyon Road
Suite 206
San Diego, CA 92131
Phone: 858-444-3344
Phone: 209-863-8928
mark@rstavares.com
www.rstavares.com
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> -----Original Message-----
> From: Haan, Scott M POA [mailto:Scott.M.Haan@poa02.usace.army.mil]
> Sent: Tuesday, November 06, 2007 12:42 PM
> To: seaint@seaint.org
> Subject: October Structural Engineer " Resisting Lateral
> Forces Cumulative overturning design"
>
> Last night I finally pulled the October 2007 Structural
> Engineer magazine off the flush tank and read the "
> Resisting Lateral Forces Cumulative overturning design..."
>
> The author says that wood shear wall overturning forces
> should be based on the moment arm from the center of the
> compression chord to the center of the anchor rod, fine...
> The article says that the only way to get accurate
> overturning forces for a multistory wood shear wall is to
> calculate the overturning moments and draw a free body
> diagram of the multi-story wall.
>
> The article says that using the unit shear times height
> method understates the uplift for multistory walls and is
> only for preliminary approximations, uh. uh. if you do it right.
>
> The unit shear times height method is derived with a free
> body diagram and summing moments. It assumes forces are
> distributed to walls proportional to their lengths. If you
> add the tension from the wall above to the tension to the
> wall chord below and use the full floor to floor heights and
> subtract out the tributary resisting loads you get the exact
> same result. If the problem is the moment arm is too long,
> you would be conservative by either designing with the wall
> lengths as the moment arm length to calculate your unit shear
> or dividing your tension by the ratio of the moment arm
> length to wall panel length. I say to anyone who disagrees
> with this to draw a free body diagram and sum the moments.
>
> I think that this article is going to cause a bunch of
> needless permitting hassles for design engineers.
>
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