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RE: California's new Emergency Structural Amendments

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Please see my reply below:

>>> SWidmayer(--nospam--at) 12/05/03 12:15PM >>>
Ben...two intersting points re these revisions (only for applicable Calif
Bldg Standards Comm./BSC projects):

	1) Sec. 1630.2.3.4-Horiz. Dist'n (Simplified Static):  "Diaphragms
constructed of ... wood structural panels ... are permitted to be considered
FLEXIBLE".  So much for the rigidity issue.  Was this the thinking of the
local ICBO structural committees?

BY: This is actually only applicable when you area using the Simplified design provisions. Simplified method has limitations on type of construction and height of the building, and the base shear is 20% higher than the regular method. The thinking is that with those limitations, the rigidities that were not considered in design can be compensated by the higher base shear, and the ramification would not be as severe due to the low height of the building. This is actually now the defacto language in all codes, IBC, ASCE and NFPA (which references that ASCE)

	2) Table 16.1-N, Footnotes 6.1 & 6.2:

	6.1:  The use of IMRF has an exception for single family dwellings
if the design uses R/Omega=3.0/2.2.  This same wording is used in Footnote
6.1 (IMRF) in the LA County Code, but this wording is used in Footnote 6.2
(OMRF)in the LA City Code.  Do you know why there is a difference?  
	This seems to be done to incourage/allow the use of welded moment
frames in SFD's only if the design is IMRF with R/Omega=3.0/2.2 (instead of
4.5/2.8).  The use of OMRF in 2-story SFD's (with restrictions to 15 psf
each for roof, walls or floors) would require the use of bolted end plates.
Is this how you read this?  Thanks,  Steve Widmayer, PE

BY: correct. This table went through many cycles of refinement! with the end product as you see in the provisions. So, if you deal with jurisdictions that have had their own amendments, you need to carefully review what they have adopted and design/review accordingly. In regard to OMF, you are correct, if your floor or roof exceeds 15 PSF, your only choice is IMF or SMF.

Ben Yousefi, SE
Santa Monica, CA

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