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Re: OMF Connection Design

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Bill,
I think that the best example of the logic of this provision is for a reinforced concrete SMRF. After you have computed the minimum reinforcing steel in the connections, you then compute the plastic moment Mp for the frame based on the actual rebar selected. You then multiply the calculated moment capacity times a 1.25 multiplier to account for material overstrength to get the Mp. Then you use the plastic moment to calculate the shears induced into the system, and you design the stirrups/hoops to resist the shears due to the frame's plastic moment. There can be no more shear than what the plastic moment can deliver. That is the concept intended by the authors of the steel provisions. Perhaps it could have been written more clearly.

The next generation ASCE 7-05 of seismic code should help. As usual, the ASCE 7 seismic section will be largely based on the preceding NEHRP Provisions. In this case the 2003 NEHRP Provisions.
The 2003 NEHRP is now available on line at http://www.bssconline.org/.

I like to read the NEHRP Provisions to my kids when I tuck them in at night. When they ask why, I read them the Commentary. They look up at me and say, "...Dad, get a life!"

Regards,
Harold Sprague

From: BCainse(--nospam--at)aol.com
Reply-To: <seaint(--nospam--at)seaint.org>
To: seaint(--nospam--at)seaint.org
Subject: Re: OMF Connection Design
Date: Sat, 3 Jul 2004 00:24:01 EDT

Maybe I'm missing something but it seems that "the frame" is the "lateral
resisting element." "The frame" consists of columns, one or more beams and the
joints connecting them.  Now the code limits the design of the "lateral
resisting element" to the maximum force that can be delivered "to" it not "within" it. It would seem, then, that the force used for design of "the frame" might be limited by a collector attached to the frame but not something integral to
the frame.
Regards,
Bill Cain, S.E.
Berkeley  CA

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