Tension and shear force at top of foundation wall from braced frame

[Shotzie]

Hello,

I'm wondering how people typically deal with large tension and shear values at the top of a foundation wall from a braced frame. It appears that following Annex D Anchorage from CSA A23.3 concrete failure will occur unless I put a pilaster in the wall. I have read the Design of Anchor Reinforcement in Concrete Pedestals LINK and that method seems promising. Does anyone have any comments or typical methods to deal with these forces?

Thanks

 

[jayrod12]

That's why we usually put pilasters unless the loads are extremely low.

 

[Shotzie]

I agree jayrod12, unfortunately this is a residential project with NBCC Part 4 elements so architecturally pilasters may not work.

 

[jayrod12]

I've had a few houses that go this route. I've always told them up front, if this is the look you want, it gets designed as a commercial building, including commercial type elements.

I'm assuming the loads are actually significant? What about providing enough reinforcement and detailing accordingly that app D doesn't apply?

 

[Shotzie]

The loads are significant enough that typical heavy hex anchor bolts without extra wall reinforcing will see failures in the concrete. I like the idea of providing enough reinforcement and detailing to bypass Annex D but I'd be concerned about fitting everything in an 8" wall, therefore I feel that it would require a bump out in wall thickness there to accommodate the steel (which is essentially a pilaster I guess).

I wonder if there isn't some sort of sort of additional framing that could be done to transfer the shear and uplift at the base of the brace into a longer portion of wall or into the floor diaphragm (and subsequently into a longer portion of wall).

 

[jayrod12]

Hence my comment about commercial building. 10" wall minimum on these crazy expensive houses. It lets me do what I need in terms of reinforcement. If they can afford 10 bucks a square foot for floor finishes then they can afford the increased wall thickness.

 

[mike20793]

Can you embed the post in the wall and anchor it to foundation wall footing? I've never done it quite like that before, so I'm not quite sure how it will fit up in an 8" wall with horizontal reinforcing on either side.

 

[KootK]

It's a tough sell to residential contractors but this is the route that I go.

1) Use threaded rebar or deformed bar anchors instead of anchor bolts and position the bars in the center of the wall. This is pretty much the only way that I know of to deal with anchor side face blowout in an 8" wall. This should cover you for tension.

2) If shear capacity becomes and issue. Embed a steel plate with studs in the top of the wall on the brace side of the column and connect your brace gusset plate to that.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Shotzie]

Great comments jayrod12, mike20793, and KootK. Thank you very much for your input! I'll look into these options to determine which is best suited for my situation.

 

[mike20793]

I tend to prefer Koot's method. It seems easiest to construct and easiest to resolve the forces. I'm not sure I'd trust a residential contractor to properly embed a column that's half the wall the depth.

 

[KootK]

The Achilles heel in my detail tends to be the need for field welding. If you introduce it in a project that would otherwise have no field welding, you'll hear about it.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[gwynn]

I agree, introducing field welding where there was none before generally doesn't make people happy. You could have drilled and tapped holes in the embedded plate, but then you would need to have a site survey after pouring the slab and prior to fabrication of the brace assembly.