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RE: Another question on Rho

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UBC 1997 1630.1.1 specifies that rho is to be applied to the earthquake load
due to the base shear, V, from 1630.2 or the componenet force, Fp, from
1632.  It does not mention the diaphragm force from 1633.  The UBC does not
explicitly state that rho does not apply to diaphragms but the SEAOC blue
book does (see

IBC 2003 1617.2.1 explicitly states that rho may be taken equal to 1.0 for
diaphragms forces given by ASCE-7 

Jason Emoto

-----Original Message-----
From: Doug Mayer [mailto:dougm(--nospam--at)] 
Sent: Friday, July 28, 2006 11:00 AM
To: seaint(--nospam--at)
Subject: Another question on Rho

Hi all,


Does rho apply to design forces for diaphragms, chords and/or collectors
(specifically in timber construction)?  A younger engineer asked me about
this today and I have always thought that it does not apply for these items.
I believe a mentor of mine stated as much in the past, but otherwise there
doesn't seem to be code evidence to back this up.  Obviously, most
collectors are designed using the special seismic load combinations (when
seismic governs), so that rules out rho right there.  Any help clearing up
this question would be appreciated.I certainly hope I haven't been laboring
under a false assumption this whole time.  Oh, I'm working with the 2001
California Building Code (UBC 97) for this.




Doug Mayer, P.E.

Project Engineer


teter a+e, LLP

Architects & Engineers

p: 559.437.0887

f:  559.438.7554

e: dougm(--nospam--at) <mailto:dougm(--nospam--at)> 

w: <> 


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