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Wood frame building over concrete tilt up

Wood frame building over concrete tilt up

Wood frame building over concrete tilt up

(OP)
I have an architect who wants to put a one story wood frame building over a one story (20' high)concrete tilt up building. Three of the exterior wood shear walls would set on the tilt up walls, the fourth would be over a truss girder. The difference in textures and appearance is appealing to the architect.

Has anyone ever hear of this being done? I can't find any prohibitions to it in the code and think the only issue might be high seismic forces in the wood frame portion. This would also be an essential facility building.

Any thoughts?

RE: Wood frame building over concrete tilt up

Neat. I've never seen it but it could be fun. Some thoughts:

1) I imagine that all of your wood to concrete anchorage would be via post installed anchors.
2) Bringing two distinctly different trades on will add cost. It might be a steep price to pay for some texture.
3) The wood diaphragm installed at the top of the tilt up may wind up being a transfer diaphragm for lateral loads.
4) You'll be inventing a lot of unconventional new details which always introduces some risk. Tread carefully.

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.

RE: Wood frame building over concrete tilt up

I have not seen this done either.

Depending on the year of the tilt-up design and reinforcing pattern, this could be a problem, particularly if it was designed using the PCA Slender Wall design procedure.

Mike McCann, PE, SE (WA)


RE: Wood frame building over concrete tilt up

Why not make the tilt-up walls 2 stories and put a wood facade on the upper story?

RE: Wood frame building over concrete tilt up

My guess is this is probably a police department and they are using the tilt up walls as the hardened area of the structure. What's the use of the wood portion? If it's not residential, you are probably in the clear in regards to the IBC. You may get nailed on using a lower R value for seismic forces, but if the wood is only one floor, then it might not be that big of a deal. I'd be worried about the load path of the wood to the tilt up, but I'm sure it can be done. Sounds like a fun challenge.

RE: Wood frame building over concrete tilt up

(OP)
It will be new construction. The top story wood framed portion will be sleeping quarters with a deck, maybe an R-2 occupancy. Is there a problem with residential on the top floor?

RE: Wood frame building over concrete tilt up

So the tilt-up portion will be new too?

Mike McCann, PE, SE (WA)


RE: Wood frame building over concrete tilt up

(OP)
Yes, it's all new construction so the walls can be designed to fit the demands. And the architect is very creative and wants one story wood over one story tilt up so that's what I try to give them. If it's a new and unique concept, they'd love it even more.

I'm only doing the feasibility study on this, so I thought I get input from other engineers. A tilt up specialist will probably get the design in the end.

RE: Wood frame building over concrete tilt up

There's some height limitations based on the use between the podium level and the wood levels above, but I think you may be okay if it's just sleeping quarters and not apartments or condos and is part of the main use of the building.

RE: Wood frame building over concrete tilt up

You may also want to look at ASCE 7-10 Sec 12.2.3 and it subsections, which has some limitations on combined framing systems such as this.

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