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October Structural Engineer " Resisting Lateral Forces Cumulative overturning design"

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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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