R Factor and Moment Frame Detailing

[sturr]

I haven't designed many moment frames, but I am working on a rather simple one that is part of a "canopy". The structure is only 15 feet tall and is very light. Snow loading generates the highest moments in the frame, not seismic. It is in SDC=D.

I would like to simply "lock up" the joints by welding/bolting with standard "old-fationed" details and beam over column joints. My question is: can I avoid the detailing requirements of the AISC 341 in any way? I seem to remember reading somewhere that if you use a Response Mod. Factor = 1.0, some of the requirements may go away.

Thanks for any guidance you can provide.

 

[rrmiv]

I haven't heard of using an R of 1. I have used R=3 to avoid the AISC 341 requirements as allowed by item #8 of IBC Table 1617.6.2. However, if you are in SDC D, E, or F, this is not permitted, regardless of the controlling load case. The seismic provisions must be used.

 

[sturr]

Thanks rrmiv.

The main thing I am trying to simplify is the column to beam connection. I have no problem meeting the strength requirements of the provisions, but I would like to avoid the weld access holes, weld backing treatment, etc. Reading the provisions for an OMF, I notice it states things such as "when steel backing is provided", or "where weld access holes are provided". It does not imply that these things "shall" be provided. Would I be in violation if I don't provide those details?

 

[sundale]

rrmiv is correct. SDC D requires a SMRF which entails using the pre-qualified connections, probable plastic moment capacity, strong column/weak beam, etc. All this seismic strength detailing stuff would be easy to satify for a one story canopy and your only issue (probably) would be having to use a pre-qualified rigid connection.

 

[sturr]

I believe I can use an OMF in this case based on ASCE 7-02 table 9.5.2.2, footnote i.

 

[rrmiv]

Of the prequalified connections (FEMA 350 and AISC 358), some have weld access holes, some have backing bars, etc. Not all of these items are used in each connection. I believe what is intended is that when you choose a connection with one of those items, you have to do it a certain way. The prequalification requires that the stipulated details of a connection must be complied with - they are not optional. Otherwise they are no longer pre-qualified.