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Design Ground Accelerations

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I can't help with the interpretation or incorporation of your geotech's
recommendations, but I can help clarify the requirements for you:  The
California Building Standards Adminstrative Code (Part 1, Title 24 CCR)is
the governing code for all public schools, hospitals, state-owned
facilities, and city and county owned essential services buildings in CA.
But, the enforcement agency for the city and county owned facilities is the
local agency, not DSA or OSHPD.

The title 24 CCR says that, for the structural design of a city or
county-owned essential facility, you would use either the locally adopted
model code (probably '97 UBC) or the local building standards and
regulations, whichever is more stringent.

Title 24 CCR requires that an earthquake hazards report be prepared (with
data about local active faults, liquifaction, slope stability, and other
seismic hazards)but this code does not mandate designs based on
site-specific or other specific ground accelerations; however, your local
building standards may require this, or it may be desired by the user, who
is probably just a different branch of the same government agency as the
building official.  The CCR also says: "All or parts of the geologic and
earthquake hazard investigation and report may be waived by the enforcement
agency when in the judgement of the enforcement agency, those requirements
are unnecessary and would not be beneficial to public safety".  (Hey, it
could happen....)

So it's the judgement of your local building official that governs your
minimum legal design.  Sounds like you, your client, the geotech, and the
building official all need to talk to each other.

Around here, loud flashing alarms start going off whenever the geotech
report even mentions ground accelerations above .6g.

Karen Casano
DSA Structural Safety Section
San Diego Regional Office





From: "Sherman, William" <ShermanWC(--nospam--at)cdm.com>
To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
Subject: RE: Design ground accelerations

There are 3 primary questions which need to be resolved:

1. Does the California Building Standards Administrative Code supersede the
local code, i.e. the 1997 UBC, for this application. 

2. What constitutes an acceptable "Geologic Hazards Evaluation"?

3. What seismic probability requirements are there? 

I can't answer these questions for you, but I have performed designs of
public utility structures which are based on such geotechnical parameters in
excess of minimum code requirements. This is usually sorted out with the
Owner before seismic analysis is performed. Were you "told" to design per
the 1997 UBC or did you "assume" that it was the "governing code"? 


William C. Sherman, PE
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com

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