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Concrete shear walls with floor openings on each side

Concrete shear walls with floor openings on each side

Concrete shear walls with floor openings on each side

(OP)
We have received a proposed shear wall layout from our architect that puts elevators on both sides of a concrete shear wall for a 15 story building (see attached image).

Is anyone familiar with analysis of this condition, that sets up a long length of wall that is partially braced at each story?

When i look at it, i see buckling effects that i wont be able to account for in my analysis and we try to steer our architects away from this condition. I want to make sure that im not being too conservative by telling them they cant go with this layout.

Thanks for the help!

RE: Concrete shear walls with floor openings on each side

Since no one else is biting.

I think you have a good point/concern - but this layout is very typical so if you say this can't work you will likely get some push back. On your sketch it doesn't look like you ever have a wall fully unbraced over it's length, i.e no slab on both sides, and it looks like you always have a return wall.

For lateral your compression block will be relatively small and near the wall end (at least in theory by strength design) so that compressive force I would say is likely well braced. More mid wall (away from ends) you may have a concern with gravity. By calc 15 stories unbraced isn't going to be good for much so you'd need to look at the horizontal spanning stiffness (between slabs/return walls etc), the wall isn't ever truly unbraced in the way that a column is. I think you'd find that the horizontal force isn't that great and that your wall can span horizontally to take it. I've never run the numbers on this - but in practice this is very common and for much taller buildings so I think you're ok.

Between each elevator is your divider beam and wall, if you're worried you could increase this dimension and put a small beam (say 10" wide) in there - that's better than nixing their layout, although maybe not necessary.

A different concern that I have with these layouts is getting your diaphragm force into the wall at each level. You need to drag all your force in through a few discrete areas.

RE: Concrete shear walls with floor openings on each side

Neat. My thoughts.

- for bending about a horizontal axis, the entire north wall of the three bank shaft may be in compression. Kinda depends on the story that you've chosen to tell regarding the composite nature of the shaft assemblies.

- The concrete text by MacGregor and Wight has an example of calculating the buckling strength of a compressed shear wall. That's the only reference, off of the top of my head, that covers it at all.

- Like Bookowski, I suspect that you can find some way to justify sufficient buckling restraint treating the unbraced chunk of wall as horizontally spanning.

- Similar to Bookowski's divider beam concept, perhaps you could replace the divider beam with a CIP dividing wall to stiffen the north wall of the three bank shaft. I've never done this myself so I'm not sure if there's some compelling elevator reason why this couldn't be done.


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: Concrete shear walls with floor openings on each side

Hi Boiler,


You could perhaps add beams between the lift shaft on the left side, but on the right side where you have three shaft it may not be possible due to space constraints.

I think you should aim to have a fair amount of gravity axial stress on the shear wall; with voids on both side this wall may not respond well with the building deformation...

How about moving the wall to the fourth vertical grid on your sketch if it doesn't affect the building torsional rigidity, layout etc..?


HTH

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