Steel Frame with infill CMU Walls

[RareBugTX]

I am designing a three story building with a steel frame (columns and beams) for gravity loads, and want to know if lateral resistance can be provided for drift by CMU infill walls at the three facade walls in all levels except one. Do you consider full bracing is provided to the steel frame by the infill CMU walls and if so, can these walls be unreinforced (minimal reinforcing 48" o.c.h. and ladder type vertical reinforcement)
Wind controls for lateral. Your feedback is appreciated.

 

[msquared48]

You'd have to check out the shear stresses on the CMU and provide adequate anchorage to the steel beam and columns. I have seen similarconstruction done in the Caribbean, but with concrete columns and beams, where the seismic risk is low to non-existant, but not in the Pacific Northwest.

Plus, after you add the CMU, wind may no longer control - re-check your seismic with the shear walls.

What kind of floor diaphragm structure do you have to transmit the lateral forces to the CMU?

Mike McCann
MMC Engineering

 

[csd72]

If you build it up solid against the frame then the CMU starts acting as a diagonal compresion strut betwwen the corners of the frame. You need to check the diagonal compressions capacity of the CMU for this.

I also agree with all that mike said above.

 

[RareBugTX]

msquared48: Thanks for replying. I am using precast hollow core concrete planks (rigid diaphragm). Here in the Chicago there is bunch of concrete frame buildings with infill clay masonry walls.

csd72:
Thanks for your input,Please let me know if I am understanding your concept, because I think your are using a more refined term for what for me is in-plane masonry shear (parallelogram type of deformation in the infill cmu wall).

Merging your concepts from msquared and csd72 I am coming to my solution. Verify proper anchorage from beam and vertical reinforcement for cmu wall, and in-plane shear capacity of infill cmu wall. I would provide reinforced fully grouted top, bottom courses next to beams.

Let me know what you guys think.

RareBug

 

[msquared48]

Personally, I would provide reinforcing at 24, with all cells grouted, but maybe that's my location talking too.

Mike McCann
MMC Engineering

 

[hokie66]

My vote with Mike on this. I don't much like to use ungrouted CMU for shear walls or bending out of plane. When you build a CMU wall, you have already bought the formwork, so why not fill it up?

 

[Structures33]

I don't know anything about the seismic in that area but there are minimum r/f requirements for anything in cat. C and worse. You might want to check ACI 530 for the seismic design requirements thay may apply. These apply regardless of whether or not seismic controls.