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Shear Wall Rho

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I am designing strengthening of an old multistory wood-framed building with several unreinforced masonry chimneys.  My system for seismic bracing of the building is to install new masonry walls aligned with each chimney in each direction so that the bracing system has enough rigidity to protect the chimneys against seismic loads.  The old building has flexible diaphragms so that each wall acts to brace its tributary area of building; no two walls are aligned.  The lengths of the masonry walls are necessarily as short as practical.  I've determined rho for each wall per equation 30-3, UBC Section 1630.1. 
 
In determining E [per equation 30-1] should a single value of rho, the highest, to be used for all of the walls in a direction, or should each wall be assigned its own rho value?  Since each wall acts independently of the others in a flexible-diaphragm system, it seems that each wall should be designed on the basis of its own value of rho, but the Code seems to imply use of a single value: the maximum.
 
Nels Roselund
Structural Engineer
South San Gabriel, CA
njineer(--nospam--at)att.net