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RE: OMF Design in Seismic Zone 4

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This is the methodology I have used....

If you use ASD, the UBC 2213.5.1 has an exception which says that if fa is
less than .3Fy, the load combinations including omega need not apply if you
comply with formula 13-3-1 and 13-3-2.

13-3-1 & 13-3-2 ===> check strong column - weak beam formulas

13-1 & FEMA 267===> check panel zone shear

Provide continuity and cover plates.

Whether or not you use ASD or LRFD you have to use the load combinations in
1630.2.1 to check drift per 1630.9.

Joseph M. Otto
Ireland Engineering
Fremont, CA

-----Original Message-----
From: Bill Allen [mailto:Bill(--nospam--at)]
Sent: Thursday, December 09, 1999 11:20 AM
To: seaint(--nospam--at)
Subject: OMF Design in Seismic Zone 4

For those of you more current in steel frame design than I, please confirm
deny based on latest technology and building department reactions for me

I would like to design an OMF in seismic zone 4. I will multiply the lateral
force by Omega sub naught (2.8) and will not take the 1/3 stress increase. I
will use the forces resulting from this analysis to design the moment
connection in accordance with the example shown in the AISC manual, p.4-106,
type 1 (rigid-frame)

As a side bar, the example on p. 4-106 has no cover plates whereas the
example on page 4-109 has cover plates bolted to the beam flange. Is either

I would like to use the more typical forces to design the members
themselves. Namely 1.0 * lateral force then take 1/3 stress increase using

I would appreciate any comments whether the above approach is either
acceptable or not acceptable by the building officials you have encountered
as well as if you feel this is an unconservative or conservative design

If there is another methodology, I would appreciate that too. I am somewhat
familiar with FEMA 273, but that document appears to be an interim doc and
not yet developed into a design tool (based on what I've read so far).


Bill Allen, S.E.
Laguna Niguel, CA