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RE: 1997 UBC EQ Requirements

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1. Regarding the Near Source factor, Footnote 1 to Tables 16-S and 16-T
allows linear interpolation between the 2 km and the 5 km distance, so you
shouldn't have a step function as you go across a street.  

2. For the OMRF designs, remember to consider the loading conditions in
Section 2211.4 No. 3.1  (Equations 3-7 and 3-8) for LRFD or 2213.6 No. 2 for
ASD.  These provisions establish a pretty healthy penalty for OMRF

Bill Cain, SE
Oakland, CA

	-----Original Message-----
	From:	Parkerres(--nospam--at) [SMTP:Parkerres(--nospam--at)]
	Sent:	Wednesday, June 30, 1999 22:54 PM
	To:	seaint(--nospam--at)
	Subject:	1997 UBC EQ Requirements

	To all:

	As you all know, the local Building Dept's here in Southern
California (LA, 
	etc.) are enforcing the 1997 UBC starting tomorrow (7/1).  We are a
firm that 
	does primarily Type V (wood) structures with OMRF steel frames.  I
have been 
	trying to get some feel from the local Cities as to what guidelines
	follow, but they do not seem as well informed as one might like.

	Currently, we are going to go with the following approach.  I would 
	appreciate the comments of others before we head too far down the

	1.  Use "Simplified Static Design" per 1630.2.3 so that we can
ignore all the 
	fancy deflection checks, etc., required for regular "Static Design".
	gives an equation of V = (3.0 Ca / R) / 1.4 W.

	2.  Assume Ca = 0.44 Na for worst case soil, Sd, without a soils
report in 
	seismic zone 4.

	3.  Assume Na = 1.3 for ALL of the LA area which assumes <2km from a
	Source Type B fault.  We bought the special seismic zone map book,
but it is 
	hard for us to justify that some areas of LA need the 1.3 factor,
but areas 
	across the street can use Na = 1.0 since they are more than 2 km
from a 
	"known fault".  Ironically, Northridge is squarely in one of the 1.0

	4.  Use R = 4.5 for light framed buildings or OMRF Steel Frames.

	5.  This yields: V = 3.0 * 0.44 * 1.3 / 4.5 / 1.4 = 0.272 W
	     The 1994 UBC gave V = 0.183 W for similar worst case scenarios.
This is 
	     49% increase in my loads!

	Comments? What is everyone else doing?

	Thanks for your input.

	Bruce Resnick, SE
	Parker Resnick Str. Eng.