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RE: Steel Connections

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Bill,

I can speak to the issue of the UBC with any real knowledge.

The IBC refers to the 1997 AISC Seismic provisions plus the 1999
Supplement No. 1 to the Seismic provisions.  It is my understanding that
the modified seismic provisions begin to incorporate some of the findings
from the Northridge earthquake and the resulting research.

Besides, as someone pointed out to me, just because the code says to do it
one way doesn't mean that you would be covered from lawsuits, etc., if the
design proved to be insufficient _IF_ there was evidence that the code
method was known to be insufficient.  The response was in reference to
dealing with OMFs and the new "detailing" requirements.  The latest
seismic provisions have some basic detailing requirements for OMFs that
make some of the standard moment connections used here is non-seismic (or
at least minimal) areas no longer able to be used without
modification...that is unless we want to use an R of 3 or less instead of
the code level R of 4.5 for OMF (BOCA code).

FEMA 267 (and 350??) are basically the reports on the findings and
suggested modifications to detailing requirements for moment connections
based upon the research that resulted from the Northridge earthquake.
Those documents will likely not be "adopted" by model codes, but will be
used to modify the AISC Seismic provisions that IS reference by IBC and
BOCA (and maybe SBC).  I seem to recall that some parts of California
might have adopted part or all the AISC Seismic provisions, but I could be
wrong on that.

Hope that helps some, but I realize that it doesn't do much with your
dilemma.

Scott Maxwell, PE, SE


On Fri, 18 Aug 2000, Bill Allen wrote:

> Thanks, Ron for your clarification.
> 
> Still more comments and questions.
> 
> If one designs the connection based on R=1, I would HOPE it would be
> adequate since it would be designed for 4.5 (in the case of OMFs) times the
> member design forces instead of a paultry 2.8.
> 
> Is FEMA-267 (or it's successor, FEMA-350) officially part of the UBC or is
> it just considered prudent to use it for the design of moment connections? I
> don't seem to see a reference to this document in the UBC. Based on reading
> the UBC *only* (without being familiar with FEMA-267 or FEMA-350), I hope
> you can see how one could use the section of the UBC I referenced then go to
> the AISC (ASD, of course) and design for Omega-sub-naught times the frame
> design forces. I'm not sure if this issue has been clarified in the IBC 2000
> or not.
> 
> And, finally, what about the exceptions the SEAOC Seismology Committee has
> taken to FEMA-350 (see:
> http://www.seaint.org/seaosc/ftp/research/Interim_FEMA_350.PDF )? Will this
> report generate a new publication by FEMA or addendum by SEAOC?
> 
> Without sounding cynical (intentionally), everything published to date
> appears to be expert witness fodder unless one succumbs to proprietary
> connections.
> 
> How much information on this topic will be covered in the Seismic Design
> Manual, Volume 3?
> 
> For those interested in the SAC seminar, you can download an application by
> clicking on:
> 
> http://www.seaoc.org/pdfs/SACSeminar.pdf
> 
> Regards,
> 
> Bill Allen, S.E. (CA #2607)
> ALLEN DESIGNS
> Consulting Structural Engineers
> Laguna Niguel, CA
> http://www.AllenDesigns.com
> V (949) 365-5696
> F (949) 249-2297
> 
> ||-----Original Message-----
> ||From: Ron O. Hamburger [mailto:ROH(--nospam--at)eqe.com]
> ||Sent: Friday, August 18, 2000 8:14 AM
> ||To: seaint(--nospam--at)seaint.org
> ||Subject: Re: Steel Connections
> ||
> ||
> ||
> ||
> ||Bill-
> ||
> ||Here's why you can't just design a connection for 3/8Rw or
> ||(Omega-0) loads and
> ||call it quits:
> ||
> ||1- The unanticipated fracture damage that occurred in the
> ||Northridge earthquake
> ||often occured at elastic or near-elastic response levels.
> ||
> ||2- The Omega-0 (and 3/8Rw) overstrength factors provide an
> ||esimate of the
> ||maximum strength demands on a structure, presuming that it is behaving
> ||inelastically.
> ||
> ||3- Thus, use of the 3/8Rw or Omega-0 overstrength modifiers
> ||might not give you
> ||adequate connections strength to assure that such fractures
> ||do not occur.
> ||
> ||You can however, design a connection using an R of 1; and
> ||ignore the testing
> ||requirement, as indicated in FEMA-267.
> ||
> ||FEMA-350, the replacement for FEMA-267, and  which is
> ||currently in publication
> ||includes a catalog of prequalified connections.  These
> ||connections have been
> ||subjected to sufficient testing and analytical evaluation
> ||that SAC feels
> ||comfortable recommending their use for general application,
> ||without further
> ||testing, as long as the connection detail is used in framing
> ||that complies with
> ||the limits of the prequalificaiton.  The prequalifications
> ||include connection
> ||details for OMF as well as SMF applications.  Both welded and
> ||bolted connection
> ||types are included.  Also included, for OMF service, is a
> ||connection that is
> ||similar, although not identical to, the pre-Northridge connection.
> ||
> ||SAC will be holding a series of seminars in September in Los
> ||Angeles, San
> ||Francisco and Seattle.  FEMA-350 and its companion
> ||publications will be
> ||distributed at the workshops.  Those who can not attend the
> ||workshops will be
> ||able to obtain copies, free, from FEMA.
> ||
> ||
> 
> 
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