Is IMF/SMF in both directions possible?

[hemiv]

Howdy all. Is it at all possible to do an IMF or SMF in two direction with WF beams and WF columns? No prequalified connections into WF column webs exist in AISC 358. It seems the only options are:
[ol 1]
[li]Make all the columns cruciform[/li]
[li]Use the Conxtech connection in chapter 10 with square columns[/li]
[li]Do the moment frame in one direction and braces or shear walls in the other direction.[/li]
[/ol]

Any thoughts from those well versed in seismic design?

 

[JoshPlumSE]

Hemiv -

You it's possible to have your corner columns as gravity only columns that don't participate in the lateral resisting system, right? Or, to have your corner columns only part of a lateral frame in one direction.

I'd say in the majority of buildings I've worked on (which is relatively few), MOST of the columns are gravity only columns that are not part of lateral frame at all. It's just that you have some pinned beams or a diaphragm connecting them the the lateral frames.

 

[hemiv]

JP

I should have clarified that constraining my question is the fact that all columns would be oriented in the same direction with respect to strong/weak axis.

I'm working in an existing building doing a mezzanine which is planned to use the existing columns exclusively. All of these columns are oriented in the same direction. Limiting which columns are part of my lateral frame doesn't help, because I'm still going to have to have the lateral system interacting with columns in the weak axis. Existing mezzanines at this location (some of them are of very recent construction) do utilize moment frames into both column axes. (e.g. AISC 360 14th, 12-4 & 5). The client wants moment frames, because that's what's been delivered in the past by others. I want to make sure I'm interpreting things correctly; i.e. that moment connections into column weak axis is not allowed for IMF/SMF

 

[JoshPlumSE]

I'm working in an existing building doing a mezzanine which is planned to use the existing columns exclusively. All of these columns are oriented in the same direction.

Well, that definitely explains the question! In that case, I think you have the summary about right. You can build up a cruciform section for sure. But, ConexTech might be problematic for an existing structure.

 

[hemiv]

That cruciform section would have to be extended the full length from connection to base of the existing columns, correct? Otherwise I'm still getting that moment back into the weak axis. Maybe not, though, since as I understand it the focus of the prequalified connections is primarily the local performance of the connection configuration itself.

Also, adding the cruciforms means doing a whole lot of CJP welding on existing load-bearing columns.

 

[JoshPlumSE]

That cruciform section would have to be extended the full length from connection to base of the existing columns, correct?

Yes, I think so. The R value and such is not just related to ductility of the connection, but to the ductility of the entire frame. The most important part of that is the connections. But, I think the Cruciform has to go all the way down.

The only way, I would terminate it early is if we're talking about multiple levels where we use cruciform on the upper levels and braces on the lower levels. Or, something along those lines. In that case, you'd have to extend the cruciform all the way down to where the frame change takes place.

 

[HTURKAK]

Yes possible.. You may choose the orientation of WF columns so , the moment resisting frames in both direction could be set up..but keep symmetry..


4. Choose the MRF 's in both directions keeping symmetry and locate the column strong axis orientation as necessary..

I understand that you are working in an existing building to add a mezzanine which is planned to use the existing columns ..
Just for curious; why you can not use gravity only beams connected to exisitng column weak axis for mezzanine ?

You may post some descriptive plans , sketches etc. to get more valuable responds..