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Re: Is SMRSF permitted in Seismic Zone 2?

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In a message dated 97-02-08 10:19:02 EST, you write:

<< In a message dated 97-02-08 07:44:44 EST, you write:
 > I feel that it is not the intent of the Uniform Building Code (UBC), 1994 
 > Edition, that SMRSF be used for buildings located in the zone of moderate 
 > seismic-risk (Zone 2). Is my view correct? I rely ... :
 The Uniform Building Code is a MINIMUM set of requirements that a structure
 MUST meet.  The Structural Engineer responsible for the design must make his
 own evaluation as to the appropriate structural system for a given set of
 circumstances.  The UBC certainly does not PREVENT ductility detailing for
 buildings in any region, it simply ALLOWS less ductility in areas where the
 seismic risk is less.
 Bill Cain, SE
 Albany, CA

I agree with Bill,  my understanding of the UBC is that either a concrete
SMRF or Intermediate moment resisting frame is allowed in seismic zone 2 .
 If you choose to use a SMRF then you must check all framing members to meet
the increased ductility,lateral displacement and reinforcing requirements of
a SMRF system.  Otherwise, if the gravity members can not handle the
displacements, then you will have failures. 

As was mentioned in the original posted question,  because of the increased
displacements that are likely to occur in using a SMRF,  there is likely to
be more nonstructural damage and cracking of concrete members which can be a
serviceability question.  The design philosophy of the UBC is to prevent loss
of life and not property damage.  In your design you may want to use the
ductility requirements of a SMRF and use a lower Rw factor than 12 to help
reduce the potential earthquake damage and increase serviceability.  You may
also want to consider what is the appropriate return period ( 70 years, 500
years, 1000 years, 2000 years, etc.) for a given earthquake magnitude to use
in determining the seismic risk to help determine if the additional detailing
for a SMRF is worth the additional cost compared to a IMRF.  In areas of low
seismicity, you should probably consider longer return periods (2000 years)
for the maximum capable earthquake (MCE) as opposed to areas of high
seismicity (1000 year return period for MCE).

Michael Cochran
Brian L. Cochran Associates
Los Angeles, CA