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Re: 1997 UBC Seismic

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On 4/27, Geroge Barclay indicated confusion over the use of the 
"omega sub 0" factor and the load combinations utilizing this factor 
in the 1997 code.


Equation 30-2, using the "omega sub 0" factor is used only for the 
design of certain elements, that can fail in a catastrophic manner 
when subjected to larger forces than required for design of the 
structure as a whole.  Specifically, this includes:

1- chords and collectors
2- members beneath discontinuous  elements of the lateral force 
resisting system. e.g. if a shear wall terminates above the first 
story, and is supported by columns, the design of those columns would 
be goverened by Eq. 30-2.
3- the axial strength of steel columns must be designed using Eq. 
4- Eq. 30-2 must be used when buildings with certain types of 
irregularities are used.

Other than the above cases (and where noted elsewhere in the code0 
the Eq. 30-1 governs.
Ronald O. Hamburger, SE
Regional Manager
EQE International, Inc.
San Francisco, California