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RE: FEMA-350 and 2001 CBC

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Gary,

Technically there are no provisions in the code that prescribe a
particular methodology for moment frame design.  Most Jurisdictions will
add the FEMA requirement or a similar locally adopted mandate.  The 2001
CBC is after all just the 1998 CBC republished with virtually no
changes.

Depending on the project, pre-Northridge OMF connections are still valid
and have a place in steel design.  This is recognized in FEMA-350,
basically this is a WUF-B.  This application is viable for smaller
redundant buildings and FEMA 350 provides a series of pre-qualification
parameters where use of this type of design is acceptable.

Under FEMA, it is recognized that the improved quality control measures
and material requirements do, in fact, justify this connection.

When you look at past performance, and why the failures in the
Northridge earthquake occurred, I believe this is consistent.  (I am
delving to totally personal opinion at this point).  The original Popov
pre-Northridge connections have performed well over time.  Along with
all the material and construction quality related issues that were
revealed by Northridge, you cannot discount the change in approach and
construction the design community evolved to during the pre-Northridge
period.  Frame buildings were traditionally highly redundant with
smaller size frame members that fit within the original testing
parameters.  In response to high labor costs designers started limiting
frames and frame connections to the minimum possible.  The result is
ridiculously large frames with very little redundancy and material
thicknesses and properties that far exceeded anything Popov et. al.
considered.  A lot of the "through thickness" and weld issues are a
direct result of the complications of creating frames with 300 pound per
foot characteristics rather than utilizing more frames of much thinner
and controlled materials that were consistent with the original testing.
Designers were extrapolating the pre-Northridge condition beyond the
pale, to where other undesirable behaviors and conditions developed that
were not manifest in the testing programs.

I believe this was an underlying concern during the development of the
rho factor, and the 1.25 maximum on frame structures as an effort to
force increased frame redundancy.



Paul Feather PE, SE
pfeather(--nospam--at)SE-Solutions.net
www.SE-Solutions.net
 
-----Original Message-----
From: Gary Grinstead [mailto:Gary.Grinstead(--nospam--at)ci.stockton.ca.us] 
Sent: Friday, July 21, 2006 10:41 AM
To: SEAINT List Server
Subject: FEMA-350 and 2001 CBC

A question for those practicing in California.  Is there anything within
the California Building Code that would require the engineer to design
his moment frame connections using the FEMA-350 guidelines?  I'm
reviewing a project where the engineer has OMF frames that he basically
has designed as pre-Northridge.  I typically use RBS connections for my
frames but I cannot find backing for not permitting his design.

Gary Grinstead
Plancheck Engineer
City of Stockton
(209) 937-5097
Gary.Grinstead(--nospam--at)ci.stockton.ca.us

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