Free-Standing Masonry Elevator

[SteelPE]

Just doing a sanity check with this one.

I have a client who is looking to add an elevator outside of an existing wood framed building. The elevator shaft is to be constructed using 8” cmu on all 4 sides with dimensions of 8’-2” x 9’-7” (I know this is not coursing, but it’s what is required by the elevator manufacturer) and be approximately 25’-0” tall. Code is IBC 2015 with Vult=131 mph

Because of the nature of the existing structure, this new elevator shaft will need to be free-standing. I have checked each wall to act independently from the other as shear walls, that is, I am not relying on the shaft to act as a continuous cantilever tube but rather 4 shear wall elements. Everything seems to be working easily. I know the walls will want to span horizontally rather than vertically, so I will more than likely add some additional horizontal bond beams to the structure.

Is there anything I am missing here? Can’t say I have ever done a free-standing masonry elevator shaft before; we usually clip them off to the support structure for stability purposes.

 

[Celt83]

Be mindful of how much wall you'll lose for the doors. In my experience they will also want the base level left completely open for the cab install and the top floor may have a larger opening requirement to accommodate the control box.

 

[SteelPE]

I did reduce the length of my wall where the elevator doors are. I do plan on having them use masonry masonry lintels for continuity of the reinforcing (no steel lintels).

Good point about getting things installed properly. However, they will need to fill in the section of wall that they leave open for installation, so I am not overly worried about that little bit.

 

[JAE]

I am not relying on the shaft to act as a continuous cantilever tube but rather 4 shear wall elements.

I think looking at the individual walls as shear walls is fine but the overall shaft will indeed act as a cantilevered tube with overall moment, axial and shear (in its respective side walls).

 

[SteelPE]

I think looking at the individual walls as shear walls is fine but the overall shaft will indeed act as a cantilevered tube with overall moment, axial and shear (in its respective side walls).

I know it will like to act as a cantilever tube in the end, but getting the walls to work individually would be a more of a "worst case scenario" as the cantilever tube should be much better overall.

 

[KootK]

I typically assume that the walls at the elevator doors will have to be entirely open. No piers at the sides. That creates a weird condition where you've kind of got a three sided building thing going on where the open side usually switches sides with not much of a diaphragm available between levels. I'd not lose much sleep over that for something of this scale except, possibly to ensure that things are reasonably stable during construction.

The largest challenge that I've had with these situations is just the lateral movement joint required at the threshold to the new building. No doubt you and your architect are already all over that aspect though.

I would do the same thing regarding the non-composite behavior. Not so much because it's true but, rather:

1) It's easy and generally conservative unless you're doing over strength plastic hinges etc. And, obviously, you're not.

2) The aspect ratio of this thing (2.5) is such that you're unlikely to develop anything resembling Bernoulli flexure anyhow. Given the proportions, the whole thing is basically one big disturbed region ala strut ant tie. So long as you can resist OT at the base, I doubt that much else will be of consequence.

 

[lexpatrie]

Something like this ---- ?

 

[SteelPE]

If what you are referring to is the white structure with the name City Hall on top.... then yes, something like that.... but no where near as fancy. Completely masonry enclosed with no windows, and the exiting structure is wood framed.

 

[phamENG]

I've done a few of these for Navy facilities. They are always on piles - the size of the footing to resist overturning isn't possible when you're right up against an existing structure. I always specified helical piles.

 

[Rusty Beam]

I know it will like to act as a cantilever tube in the end, but getting the walls to work individually would be a more of a "worst case scenario" as the cantilever tube should be much better overall.

this makes sense. but you may still want to check torsion that may arise due to tube behavior rather than individual walls.

 

[lexpatrie]

The masonry on that one is a veneer, as I recall, there's a steel moment frame inside in both directions and it's on some kind of special foundation, pit depth probably undermined the existing foundation a bit as well. Naturally when you show a 4' pit they want a 5' pit and when you show a 5' pit...... it's possible there's some kind of slide connection between the new and the existing, but when one considers the two-sided "box" and potential settlement you're trying to adjust for like four different movements.

 

[haynewp]

Check the gap between the shaft and main building meets the separation required by ASCE 7 if this is a seismic area.