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RE: 2007 CBC special seismic load combinations

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This is a good question. I am also kind of puzzled by the language in the IBC/CBC requiring that both the LRFD and ASD design be based on the same load combination! I personally hope this is an oversight and not a deliberate attempt at superseding ASCE 7. Substantial time an effort was put in creating section 12.4 of the ASCE in order to consolidate and simplify the load combinations involving seismic loads. Equations 5, 6 and 8 along with section of the ASCE 7 make a lot more sense to me than the IBC provision.


Ben Yousefi, SE, CBO

Chief Building Official

City of Mountain View, CA

(650) 526-7007


From: Mark D. Baker [mailto:shake4bake(--nospam--at)]
Sent: Saturday, May 24, 2008 11:12 AM
To: seaint(--nospam--at)
Subject: 2007 cbc special seismic load combinations


I’ve been away from the list for quite some time, I have looked through the archives for messages on this topic and found none.


Should we be using the CBC Equations 16-22 & 16-23 or ASCE 7-05  section Equations 6 & 8?


I do not find any reference in the CBC which requires the use of the ASCE equations. My confusion comes from the Seismic Design Manual Volume 2, Ex. 2 using the ASCE equations for the uplift of shear panel on a beam.






Mark D. Baker

Baker Engineering