Steel column to CMU considerations

[Bammer25]

Seems pretty straight forward but I just want to make sure I’m not overlooking anything. Have some pretty heavy reactions (100 Kip) coming down through tube steel columns and due to grade falling off I will need to land on 12” cmu stem walls (more likely I’ll make pilasters at load points).

I’ll check the cmu for concentrated loads and design the anchorage and base plate. This is residential and the loads are coming from a roof top pool in case you were wondering how they were so high. Anyway I have the stability worked out just wasn’t sure if I should avoid anchoring to the CMU. If I bring the columns to grade they will be nearly 45 feet long on the steep end

 

[XR250]

Well, there is no free lunch. Are you sure you have the stability worked out? Even a small eccentricity @ 100k can be a problem for a stem wall.
Likely cheaper, easier and more reliable to increase the column size and run it to grade

 

[Bammer25]

Well the columns will be hidden inside the exterior stud walls so I can’t really do any diagonal bracing unless you have a cool idea there.

I had planned on moment connections for stability.

The pool will be cast on decking so I don’t really see the need for plan bracing in the upper beams but that would be easy to install.

 

[XR250]

I thought you meant stability of the stem wall.

 

[Bammer25]

I just figured if I did a 24x24 pilaster that wouod cut it. I haven’t ran any numbers down there yet. Just sized the beams and columns

 

[phamENG]

How tall is the stem wall? The pilaster would have to cantilever up from the ground to a pin at the column base. You could do a moment base for the column into the CMU, but if it's hidden in an exterior wall the eccentricity is going to make that a challenge.

I'm with XR - run the steel all the way to the footing.

 

[Bammer25]

Looks like worst case the wall will be 26 feet tall. Ouch. Can I pick another lot?

 

[XR250]

"I bring the columns to grade they will be nearly 45 feet long on the steep end"
"Looks like worst case the wall will be 26 feet tall. Ouch. Can I pick another lot?"
How does that work?

 

[Bammer25]

Not sure what you mean. Stem wall up to basement level. Grade falling off toward the back. 12 feet between floors

 

[XR250]

Well your original post did not go into that much detail for us to know that.
Is your stem wall braced by the basement floor system?
If so, it ain't a stem wall.

 

[Bammer25]

No…it’s a stem wall

 

[phamENG]

Can you give us a section through this thing?