Mike,

New FEMA reports are out and perhaps that is the first time that the lay
people have heard of this.  Those in the business, I'm a structural
engineer, have known about this shortly after the Northridge quake.

Buildings, of course, were inspected as part of the normal process with
FEMA, ATC (220 and 221) and at one particular building where some
retrofitting or rehab was underway a crack was found in the connection which
propagated through the column apparently originating in or around the welded
joint.  This, of course, not only leaves the column vulnerable but
undermines the vertical load system - bad news.  In buildings its better to
place a fuse (localized yielding - damage) in the beams.  Thus all
post-Northridge special moment resistant frames (SMRF) were based on this
idea.

The areas are hard to find as you might imagine...there is wall board,
sheathing, and fire protection on the steel frame.  They only reason the
cracks were found was because of a rehab job already underway where all that
material was ripped out.

New connections make use of a number of methods.  Too many to list here.
One method however, is to "neck" down the beam near the column so that the
beam is weaker due to lack of section properties.  The damage will manifest
there rather than in the column.

Hope this helps.  If not and you would like some reading check out any steel
magazine or log onto www.EERI.org and search through some old SPECTRA
articles.

-----Original Message-----
From: Mike Price [mailto:mprice@.........
Sent: Friday, April 20, 2001 1:50 PM
To: PSN
Subject: FEMA report on steel buildings


Yesterday CNN reviewed a FEMA report that steel frame buildings,
especially those built prior to 1994, contained a design
flaw that concentrated temblor stresses at weld points between
beams. New designs move stresses into the beams themselves
for increased strength. Apparently this failure mode was
observed in Kobe.

Can anyone point to more in-depth information about this?
If design changes were introduced in 1994, why is this news
now? Have there been analyses of high-rise, steel frame
buildings in LA or San Francisco that indicate they are
more likely to be damaged than was previously thought?
What design changes were introduced?

Thanks,
Mike Price
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