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RE: Shear Wall Rhos

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Nels:
Ditto.  The code requires the redundancy to apply to the building not the bracing line or element.   The idea is for the whole system to be stronger to pick up the slack if the component fails, not for the component to be stronger by itself.
 

Scott M Haan P.E.
Plan Review Engineer
Building Safety Division
Development Services Department
Municipality of Anchorage
http://www.muni.org/building
phone:907-343-8183 
fax:907-249-7399
mailto:haansm(--nospam--at)ci.anchorage.ak.us

-----Original Message-----
From: Yousefi, Ben [mailto:Ben.Yousefi(--nospam--at)ci.sj.ca.us]
Sent: Tuesday, August 13, 2002 7:54 AM
To: 'seaint(--nospam--at)seaint.org'
Subject: RE: Shear Wall Rhos

Nels
 
The redundancy factor is applied to the entire building not each line of resistance. Even along the height of the structure, if you notice, the UBC, in calculating the "r max" factor, considers the highest "r" for lower two third of the height of the building. In the IBC, even this was eliminated and the highest r along the entire height of the building should be used in calculating Rho for all levels. The only break is given when you determine the force level in each direction. In that case, you may have different rhos for each direction of loading.
 
Ben Yousefi, SE
San Jose, CA
-----Original Message-----
From: Nels Roselund, SE [mailto:njineer(--nospam--at)att.net]
Sent: Tuesday, August 13, 2002 8:12 AM
To: seaint(--nospam--at)seaint.org
Subject: Shear Wall Rho

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