Moment Connection to Concrete Wall???

[shuff213]

Working on a project using Insulated Concrete Forms for the exterior wall system. Steel framing will be used at the building interior.

We have conditions where horizontal beams are framed to (as well as bearing) the ICF walls and are considered moment frames.

I'm thinking a moment connection could work where an embedded, vertical plate with headed studs is cast into the concrete wall, and then top and bottom plates are bolted to the wide flange beam. These top and bottom plates can then be welded to the embedded plate, similar to a typical moment connection.

Any thoughts on a moment connection where the beam bears on the concrete wall (bearing required due to the magnitude of the gravity load)? There will not be any concrete above the beam's top flange for any sort of connection.

Our concrete wall thickness is 6.25".

Thank you.

 

[connectegr]

I would not recommend bolted paddle plates to an embed plate. Embeds and concrete walls are rarely located exactly, so the connection needs field adjustment. I don't recommend welding to the embed in the field, because this can generate a lot of heat.

I am not aware of any bearing connection that can transfer moment through the bottom flange only.

I hope the moments are very small. Because the embeds must be designed for moment with tension in the anchors. 6.25" wall thickness may be a little thin, especially if the embeds are located near an edge.

Sorry for the lack of suggestions. We rarely see concrete walls included in moment frames. Typically moment frames are contained within the steel structure. Concrete shear walls maybe used orthogonally, but the moment connections will stop at the last steel column. Beams connections to the concrete wall are for shear only.

http://www.FerrellEngineering.com

 

[iponom]

Something like this maybe?

Not sure though looks like a lot of welding.. and need to cut a pocket for this one...
anyone have comments about this detail (other than that its not 100% complete)?

 

[connectegr]

iponom
Nice detail

But, a mentor once told me "a moment is not smart enough to turn a corner". Therefore, I always look for the couple forces and transfer the moments as axial forces in a single plane.

Will the tension in the top flange translate to the vertical end plate? And then vertically through the bearing plate?

And the results, is a lot of forces that concrete does not like. Tension, moment, shear...

http://www.FerrellEngineering.com

 

[iponom]

Well, I assumed the wall was designed for moment bending.
As to a corner.. I think the moments are smart enough to turn a corner.. at least that's what I've been taught in school with simple moment frame design...

In this case I see the couple distributed along the ~6.25" (wall thickness) lever arm... no?

 

[iponom]

That's a tough one.. wonder what shuff213 will come up with in the end..

 

[iponom]

Connectegr,

I think I might have applied to work within your company couple months ago... How are you guys doing in this economy, are you hiring or firing?

 

[JAE]

iponom,

Your moment connection is feasible but keep this in mind...the stiffness of your wide flange vs. a 6" wall is drastically different such that the beam will almost certainly behave as a simply supported beam no matter what you do at the end.

If you fix your very stiff beam to a wet noodle, it still behaves as a simple end.

The wall will crack so your stiffness will be more like a percentage of the I_gross of the wall for a fairly limited width (4t wide?).

Why spend all that money for no gain?

 

[iponom]

JAE,

Well I am not sure what you mean when you talk about stiffness differences. What failure mode do you have in mind?

What I was thinking about is restraining the rotation at the end of the beam.

 

[JAE]

Restraining it with what? The wall is only 6 inches thick - it has very little stiffness to restrain the beam at all.

Force follows stiffness. Per my analogy above - if the wall was a flexural wet noodle, the moment in the wall would be ZERO.

In your case, the wall is only a 6" thick, cracked wall with a transformed, cracked, effective I = 20 in^4 compared with your beam with perhaps an Ix = 2200 in^4.

 

[iponom]

Restraint for really really really really small moments

I agree 6in is nothing - but who know what kind of beams and moments we are dealing with here....

 

[iponom]

why even bother connecting it, maybe just have the beam cantilever over it...with a beam pocket and leave it at that...

 

[JAE]

Yes. I agree: why restrain it?

And you (in your first post) seemed to indicate that the wall/beam connections were part of a moment frame. This may not be stable if all you have are 6.25" walls with essentially "pinned" connections.

 

[connectegr]

iponom,
My comment concerning the moment "turning a corner" was intended as a connection design concern.

Regarding our workload...
I think it is slow everywhere. We have work, but primarily because of the number of clients we service. We have not seen any big projects in a while, mostly small projects and miscellaneous. We are not hiring at this time, but luckily we are not firing either.

http://www.FerrellEngineering.com

 

[iponom]

Well I didn't start the topic.. and in my original post I assumed that the wall was stiffer than your typical 6in wall...

I've never seen steel moment connections to 6in conc. walls, but I do think there are some to 4ft thick conc. walls out there...

aren't there monolithic concrete frames that sustain moments- maybe replacing the steel beam with series of concrete beams would work out better, more costly?