2006 IBC OMF analysis procedure 1

[ampersand]

I am flummoxed. I'm in California; we just switched from UBC to IBC. I cannot, for the life of me, nail down just how to design an OMF. I frequently design one-story steel OMFs supporting wood-frame structures (homes, small apartments), but the new code has me confused.
I don't want to design IMFs or SMFs- too time-intensive. UBC used to make you design OMFs by using the scaled-up-by-omega load combinations, and then use full-penetration welds for the connections, and not have to get involved with the FEMA 350 design procedure (ugh!) It appears that IBC says that the required flexural strength must equal "the maximum moment that can be developed by the system", or (1.1/1.5)RyMp, whichever is less.
I want to understand this. I am looking for two answers, and I will be enormously indebted to anyone who can make me understand either answer. First, what does "the maximum moment..." mean? How do I determine the maximum moment. Do I then take this maximum moment, and design the connection according to ASD methods, using the ASD load combinations? Second, if I use the (1,1/1.5) equation, it seems that (1.1/1.5)RyMp=0.8*max. plastic moment. Is Mp equal to Zx times the ultimate steel stress? If so, it doesn't seem like this method increase the required strength very much, since the goal of OMF design is to ensure minimal inelastic deformations...
I have called some big, established firms in the SF Bay Area, and although everyone is very friendly and willing to discuss this matter, their answers are all, "We don't know either. We're all trying to figure it out." I will do anything to understand this. I will fly to your office, anywhere in the country, to consult with you... Help!

 

[prsconsultant]

What R value "Building response modification factor" are you using?

What is the seismic design category?

Do you have AISC seismic design manual? If you don't I can scan an example and post it.

 

[ampersand]

Hi PRS, thanks for the quick response. The project is in SDC E, and I am using R=3.5. I do not have the book you mentioned.

I have the 2006 ICBO Structural/Seismic Design Manual, Vol. 3, but it only designs a SMF.

A scanned example would be much appreciated.

 

[ampersand]

Just thought I should mention that I do have, and have read through, ASCE 360 and ASCE 341. But there aren't any example designs in these publications.

 

[prsconsultant]

ampersand:

Look at the attached example. Let me know if you need any more info.

 

[MarkAJohn]

I'm also in the SF Bay area, but I haven't had to do one of these yet. However, there are a couple of FEMA 350 pre-aualified connections that don't look too bad. Not to mention that SMRF can be used in more situations.

my $0.02
MJ