Column of Special Reinforced Concrete Frame 3

[BONILL]

A column part of a special reinforced concrete column is supported at the top by a two way concrete waffle slab with special reinforced concrete beams on both directions, and at the bottom by a two way concrete slab consisting of ordinary reinforced concrete frames (since in that floor special reinforced concrete shearwalls are being used as the lateral force resisting system).

My question is the following:

Do the special detailing requirements (i.e. closer stirrup spacing/no splicing @ hinge locations) for the the special reinforced concrete column start at the top of the bottom floor up, or is the part of the column within the slab (between the top of the bottom floor and the bottom of the bottom floor)also subject to those requirements?

In other words, can I splice the column reinforcement of the ordinary reinforced column and the special reinforced column at the joint and/or do I need to provide stirrups in this location?

Hope this is clear enough.

 

[a2mfk]

You'll get better and more help with a sketch or two.

 

[BONILL]

Please see attached sketch.

 

[ble31980]

In my opinion you should reinforce the joint as a special moment frame joint. My reasoning for this is because the column has to be able to transfer the lateral forces into the diaphragm before they can be transferred to the special shear walls, hence the special moment frame ends at the bottom of the diaphragm. To insure that this is going to happen, the joint needs to be per 21.5 of ACI 318.

 

[PUEngineer]

I agree with ble, but might even go as far to say that I would detail the reinforcement for the column in the level below and the adjacent beams as if they were part of a special moment frame. If that upper column is fixed at the transition, then all those elements have to be ductile enough to transfer those forces and go through those special moment frame rotations.

 

[sandman21]

I am not exactly sure where the building is, however OMF's are no permitted in seismic design category C-F.

 

[ble31980]

That confused me at first, too, sandman, but I think the SFRS will be special shear walls on the level below the special moment frame. He probably shouldn't call them ordinary concrete frames in his sketch. I think he meant that the frame system transitions to a gravity only frame with special shear walls.

 

[BONILL]

Yes. I should have called it a gravity only frame instead of an ordinary moment frame. I do think that the joint should be a moment resisting one as well.

 

[sandman21]

I would say that I would meet any SMF requirements at that joint, you have an in-plane offset transferring load to the shear wall, the moment and shears need to transfer into the beams to go to the shear wall. In-plane or out-plane offsets have been shown to have a major detrimental effect on building performance during seismic they are one area I would be extra conservative on.

 

[wannabeSE]

The special moment resisting frame detailing may need to continue to the foundation. See ASCE 7-05 section 12.2.5.5 and ACI 318-05 section 21.2.2.3