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Seismic Design in the Pacific Northwest

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I have been looking at seismic design criteria in the UBC (and some other
documents) for Washington and Oregon to get preliminary information on
possible earthquake performance of buildings in the Pacific Northwest.  

Since 1967, UBC seismic zonation of Oregon and Washington has changed
radically.  I'm trying to get some sense of whether and when seismic
considerations have been incorporated in the design of buildings in the
Pacific Northwest.   

Some of what I have been able to glean from the UBC and other sources
follows, as does some general questions regarding seismic design in Oregon
and Washington.  I'd appreciate any insights those of you with experience in
the Pacific Northwest have regarding seismic design in this area.

Thanks in advance for your help.

=======================================================
Chris Deneff
E-mail: deneff(--nospam--at)allendale.com
=======================================================

Oregon
My understanding based on some literature I have read is that:
1.  Since 1974, all buildings in Oregon have been required to conform to the
Uniform Building Code.
2.  In April, 1996 the state code was based on the 1991 UBC.
3.  The Oregon State Building Code Agency assigned western Oregon to Seismic
Zone 3 in 1991.
4.  The UBC Seismic Zone in western Oregon is currently Zone 3, but was Zone
2B in 1988 and 1991 and was either Zone 1 or 2 from 1970 to 1985.  The UBC
Seismic Zone in eastern Oregon has been Zone 2B (in general) since 1988 but
was either Zone 1 or 2 from 1970 to 1985.  

Questions:
1.  The 1991 UBC puts most of Oregon in UBC Zone 2B with a small area of
Zone 3 in Lake County.  Western Oregon was changed to Zone 3 in the 1994
UBC.  Has design in western Oregon been based on Seismic Zone 3 since 1991
based on the Oregon State Building Code Agency requirements? If not, Seismic
Zone 3 has been used for design in western Oregon since what date?

2.  Prior to 1974, was it typical to consider seismic design?  How about
after 1974 - was there lag time in incorporating seismic design or were
requirements enforced?

3.  On a broad brush basis, are there dates of construction that would
indicate that seismic design has or has not been incorporated?  For example,
for western Oregon, would it be reasonable to say that if the building was
built after 1991, it most likely was designed for Zone 3 forces and 1991 (or
1988, or 1985 etc.) UBC design practices?  How about for eastern Oregon?

Washington
My understanding based on some literature I have read is that:
1.  Since 1975, all buildings in Washington have been required to conform to
the provisions of the most recently adopted Uniform Building Code.  
2.  In April, 1996 the state code was based on the 1994 UBC.
3.  The area near Puget Sound has been UBC Zone 3 for many years (at least
since 1952).  However, the area of Zone 3 was extended considerably east and
south in the 1970 UBC and again in the 1988 UBC, and was extended south and
west in the 1994 UBC.  

Questions:
1.  Has design in the Puget Sound area been based on Seismic Zone 3 since
1975 when the UBC was adopted or was seismic design generally incorporated
prior to that date?

2.  Has seismic design in western Washington, which is now all in Seismic
Zone 3, been incorporated since 1975 (although maybe to the code applicable
at the time)?  Have Zone 3 requirements been enforced in western Washington
as those areas have been rezoned in the UBC or has there been lag time?  

3.  How has seismic design been handled in eastern Washington (the area that
is now Zone 2B)?  

4.  On a broad brush basis, are there dates of construction that would
indicate that seismic design has or has not been incorporated?  Are these
different for different regions (for example, the area surrounding Puget
Sound, other areas of western Washington, and eastern Washington)?