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Re: moment frame conn. per FEMA

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We design many small OMRF frames here in LA City and use the following
guidelines to get around the fancy connection design.

The City lets you use a Rw= 2.67 for connection design in OMRF's with flexible
diaphragms.  This is equivalent to Rw / (3Rw/8) when Rw=6 for OMRF.  To
accomodate this requirement, we run our frames in the computer using a scaling
factor of 2.25 (3Rw/8) times the seismic forces on the members.  We check the
members with a 1.33 increase as allowed per Code.  If the entire member works
for this greatly increased force, we then assume that a typical, pre-
Northridge flange-welded, web-bolted connection is adequate without cover
plates, etc.

We then check the frame for drift without the 2.25 scaling factor.  Since
drift governs anyway in many cases, we are not paying any premium in the steel
cost and are saving in the connection cost.  Plus it greatly simplifies the
analysis for a small frame.

Good luck,

Bruce Resnick, SE
Parker Resnick Str. Eng.