Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

1997 UBC EQ Requirements

[Subject Prev][Subject Next][Thread Prev][Thread Next]
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 to 
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 path.

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".  This 
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 Seismic 
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 zones.

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 
a 
     49% increase in my loads!

Comments? What is everyone else doing?

Thanks for your input.

Bruce Resnick, SE
Parker Resnick Str. Eng.