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Re: 10/lw term in calculation of rho

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The two guys that ran the S.F seminar didn't know wood very well at all.
As Bill Allen correctly pointed out in previous comments on this subject, rho
doesn't "penalize" short walls at all.  What this provision really does is set
a limit on the the maximum shear in any wall at each level.  Set rho = 1 you'll
find that Vmax = 2 x story load/square root of the base area.
It actually works very well for design purposes. Once you know the story loads
and base area, find Vmax, add up the total length of shearwalls for each floor
and find Vave. at each level, if it exceeds Vmax. you're going to add some more
wall length on that floor to keep rho under 1. As long as you don't mix long
and short walls (under 6') and keep the eccentricity down, you'll find this
works very accurately.  If you let rho exceed 1, then the wall loads go up and
rho goes up again--it usually takes several iterations to converge (or hit
1.5).  You almost have to set up spreadsheets to do lateral analysis now.
Chuck Utzman, P.E.