Elevator Openings In Concrete Core Walls

[ProbingStructuralEng_03]

I have recently worked on a project where there was not much insight between the architect or other structural engineers on how required elevator openings are handled for concrete core walls acting as lateral shear walls for the building. The elevator manufacturer's, which have unique requirements, have a rough opening required at each floor and occasionally these openings are are almost the entire width of the wall face giving access to the elevator. The final elevator doors require much smaller openings and it seems overtly excessive to just allow the rough opening to punch an entire hole in your lateral system. I am trying to see how others commonly handle this issue. Is it common to just allow the full width of the wall be removed for construction purposes or is it common to require the wall reinforcement to have continuity for filling back in the wall once the need for the larger rough opening is done?

 

[Aesur]

I haven't needed to use a concrete core elevator to date, but for masonry ones we tend to leave one entire side open with a lintel spanning across, if they end up infilling a portion with CMU after, it's just infill.

 

[dik]

I've done the same with concrete... just treated the core as a 'U'. I've designed shear walls as 'coupled'... but that's about it. I've not done any 'real' highrises... limited to about 30 stories.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[KootK]

X3. The returns are nice to have in terms of bracing the side walls a bit but planning for the returns seems to be a project management nightmare. When you plan to have them, you have to:

a) Coordinate them.

b) Potentially fight for them.

c) Potentially have to accept losing a fight for them.

Even if you get the returns, they often have control crap built into them anyhow.

 

[dik]

They often have slight returns... I've generally ignored them, other than including them as part of the section properties.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[EZBuilding]

Note that the elevator cab themselves are placed inside of the shaft after the structure is built. In a single elevator shaft - there is a physical need for the wall leave-outs.

 

[ggcdn]

Its common in North America to not include the returns and just design a three-sided / C-shaped wall. Usually they need the largest opening at or near the ground floor for installing the cabs.

 

[ProbingStructuralEng_03]

Thanks for the replies everyone. I think I am on board with just sticking with a C shaped core. Too much of a pain to rely on the punched portion of wall.

 

[WesternJeb]

I would like to piggyback off of this. For special concrete shear walls (high seismic), I have a hard time seeing how the wall with openings isn't going to take significant load unless there are expansion joints detailed. Structures act how we detail them, not how we design them.

If the wall with openings begins to take load and is not detailed for ductility (i.e. wall piers, coupling beams, etc.), then wouldn't it fail prematurely compared to the rest of the structure? So should we be ignoring it for capacity, but still detailing it for the ductility? At that point, it makes sense just to include it in our design to myself.

Thoughts from others on how to detail that portion of wall?

 

[ggcdn]

I normally make the returns/ that side a nonstructural wall. It’s both designed and built as a c shape wall.

 

[bones206]

WesternJeb - this question has come up before: thread507-485941

There are links to other threads on the topic within that thread as well.

 

[WesternJeb]

Thank you Bones206!

 

[bones206]

My take on the elevator opening thing is that any structural element that ties into the designated lateral walls should be detailed to ensure it won't cause damage to the shear wall boundary elements in an earthquake. Whether something is deemed sacrificial or not I guess depends on the target performance level of the building, but we should still consider the potential interaction effects that could occur between lateral and non-lateral elements. Also if the coupling beam is functioning as a gravity header, I wouldn't want that failing and so the detailing should ensure ductility.

 

[WesternJeb]

Those match my thoughts as well, just wanting to make sure I wasn't being excessive. Thank you.

 

[KootK]

If the wall with openings begins to take load and is not detailed for ductility (i.e. wall piers, coupling beams, etc.), then wouldn't it fail prematurely compared to the rest of the structure?

You raise an interesting point. I don't feel that the collapse of the return walls represents any meaningful danger with respect to the overall structural stability of the building. However, one could argue that excessive damage to those return walls might jamb the elevator door and/or render the controls inoperable. That might be undesirable in a building that folks are trying to get out of in a hurry. I've not yet seen anyone pay any explicit attention to this aspect of elevator design.

Thoughts from others on how to detail that portion of wall?

I feel that a good, general approach would be to design those wall piers to survive the anticipated drift of the building as we are allowed to do with "gravity" columns in shear wall towers. And I could see this being difficult to accomplish for a "general notes" sort of masonry infill wall with, perhaps, some controls embedded into it.

Those match my thoughts as well, just wanting to make sure I wasn't being excessive.

That depends on what kind of sacrificial / non-structural return wall you're contemplating (it's not clear to me from your post);

1) If you are thinking of the return walls as concrete elements cast contiguously with the rest of the core wall then I would say that most designers probably would detail those elements for ductility similar to typical shear wall zones.

2) If you are thinking of the return walls as CMU infill etc, then it is my experience that nobody is really paying any attention to their seismic survivability at all.

For the front walls of most elevator shafts, coupling beams will be pointless / impossible:

a) The wall piers will usually be too narrow to be able to produce any meaningful coupling behavior.

b) The wall piers will usually be too narrow to be able to accommodate the rebar detailing required for proper coupling (X-bars developed 2 x Ld etc).

 

[WesternJeb]

Thanks for the thorough reply, Koot.

I see your point but disagree with your first comment IF the coupling beam has structure bearing on it (as mentioned above).

I don't feel that the collapse of the return walls represents any meaningful danger

I appreciate the rest of the comments, I think they all make sense to be used on a case by case basis.

 

[KootK]

I see your point but disagree with your first comment IF the coupling beam has structure bearing on it (as mentioned above).

That's just an ordinary gravity beam and not a coupling beam then, right? Yes, the beam's connections to the piers ought to survive anticipated drift and all that jazz but that still does not make the beams coupling beams. Obviously, I agree that loads coming in from above ought to have support below...

 

[WesternJeb]

I see what you are saying now. Thanks for clarifying!

 

[jayrod12]

However, one could argue that excessive damage to those return walls might jamb the elevator door and/or render the controls inoperable. That might be undesirable in a building that folks are trying to get out of in a hurry. I've not yet seen anyone pay any explicit attention to this aspect of elevator design.

I've never done a super tall building, hell not even a tall building. But, are elevators expected to remain operable in a design level seismic event?

 

[KootK]

I, also, am no expert on big money vertical transportation systems. And I'm not sure that it's yet a standardized thing for the supertalls. My general understanding is this:

1) Plan for the elevator service to be disrupted. Do have stairs and take them if you're able.

2) If one were in an elevator cab during and earthquake, it would be nice if one were able to get out of that cab.

3) Elevator cabs should progress to the nearest floor where maintenance folks can, ideally, deem them safe for use.

4) It's tough to fully separate earthquake risk from fire risk. So it would be great if limited mobility folks on the upper floors didn't have to traverse 90 flights of stairs to safety.