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RE: Ceiling Lateral Bracing

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Medi,

I have done design work all seismic zones.  The code is not specific in what
to do for seismic zone 1 (as it should be), but if there is no applied force
prescribed in the code, the practice is to not provide the bracing.

Kansas City in older codes, was a seismic zone 1, and the ceilings were not
braced.  From the early 80's Kansas City went to a seismic zone 2A, and some
of the firms started to require braced ceilings.  When the 2000 IBC comes
out we will show that the braced ceilings in the 80's and 90's were not
required for Kansas City.  Such is the progress of our code development.

By the way, the most effective system for bracing ceilings is the Chicago
Metallic Dyna Strut system (a rigid system), which may have died from
neglect.  In actual earthquakes the UBC system has not been as effective as
assumed (it takes a lot of movement to tighten the wires).  The UBC system
is not too effective, but it is cheap, and "we've always done it that way"
(I hate that statement).

There was some research on this topic that I dug into a few years ago.

My advice would be to look at the 1997 NEHRP and see if the requirements
might be kicked in with the 2000 IBC.  If it looks like they aren't required
now, and they won't be required in the foreseeable future, save your client
some money and delete them.

Regards,
Harold Sprague
The Neenan Company


-----Original Message-----
From: Medi Givechian [mailto:GIVECHM(--nospam--at)sverdrup.com]
Sent: Friday, July 23, 1999 11:17 AM
To: harold.spraque(--nospam--at)neenan.com; seaint(--nospam--at)seaint.org
Subject: Ceiling Lateral Barcing


Harold:
Thank you for your response to my question in the seaint list server. You
stated that lateral bracing and compression struts are not required in zone
one (1). Is this your opinion or you may have a reference?  Is your company
involved in ceiling installations? Basically I need some good reasoning to
convince an owner that we don't need bracing, since it was not included in
our construction budget. Please reply. 

Thanks again
Medi Givechian, P.E.