Elevator in 3-story Wood

[Guastavino]

Folks,

This is my first rodeo with an elevator in a multi-story all wood framed building (Endura 3500# model by Thyssen Krupp). A few questions:

1. In the past with steel structures I didn't care about the hoist beam reaction in terms of how often it is utilized. The steel was good whether it was a constant load or a onetime thing. Somewhere I think I heard that the hoist load is a one time deal (or rarely needed). I'm thinking wood creep, etc. Am I imagining hearing that?
2. Arch has the 2.5" steel stud shaft walls that I'm surrounding with multiply LVLs at the floor levels. The rail forces seem small (3500# elevator) based on the submittal I have. Is this what is typically done?
3. Does anyone do the hoist beam out of wood, or just do steel? Im considering running steel tubes in the walls the entire structure height with a steel beam and moving on. (Of course, bracing the steel column at each floor level too.
4. Any other things I need to be thinking through?

Thanks,

Nick

 

[TehMightyEngineer]

Did a design of a 5 story one recently.

Short answer; don't do it. Long answer is you can do this but it's likely easier to just use concrete or a masonry shaft. Mostly for fire protection reasons but structural as well. Check out my topic here: [URL unfurl="true"]http://www.eng-tips.com/viewthread.cfm?qid=378935[/url]

A google search can turn up a lot as well.

1. I would consider it infrequent enough to not worry about creep.

2. I used a multi-ply LVL built-up using SDS screws. The biggest issue I faced was not strength but deflection, make sure the rail supports are sufficient. My elevator was one of the ones without a machine room so you may have some different loads than I did. However, I remember my rail loads weren't that large either. Definitely check those deflection limits though, they're really small. The elevator manufacturer can provide a lot of design help.

3. I would only try this with a steel hoist beam. Trying to do that out of wood seems like a recipe for disaster. Steel beams for the rail supports would be better but as I found you can do it with wood for the rail supports.

4. FIRE! Fire protection is critical. The shaft must be fire rated per the code and this typically will be an unbroken fire barrier on the roof, walls, etc. This is very hard to detail with plywood and gypsum wallboard but can be done.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[Guastavino]

Thank TehMighty.

1. Thanks for the google/eng tips links. I actually looked up some of those and my main question is in regards to the frequency of the hoist beam load which I couldn't find.
2. So the arch (see below pic) is showing those 2.5" steel shaft wall studs. I plan to put a 2-ply LVL right behind that. Do they attach the rails to through that wall to the LVLs on either side? I'm not sure how that all works, but I want to have something for them to attach to. The stud walls are outside of my scope (IE archs).
3. How do you calculate the deflection you mention? If they connect to my LVL's at the floor, it won't be any more than the story drift because it's all tied to the diaphragm, which it will be anyway. Maybe I'm missing something?
4. Fire protection is architect's baby. I want to be accommodating though.

Attached is the arch plan.

Thanks!!!!!

 

[TehMightyEngineer]

Nothing attached.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[Guastavino]

Sorry about that. Try this

 

[TehMightyEngineer]

1. My understanding was the hoistbeam is typically only used for initial install and then any major equipment changes after that.

2. I had them attach the elevator to the LVLs through a steel plate (which was provided by the elevator manufacturer) and a wood squash block with SDS screws.

3. I used the NDS deflection equations for a wood member. However, the issue I found is there is no research (or at least none I found) on nail/screw slip between plys which will add to the deflection. To hopefully remove this ply-slip deflection I had them glue the plys together as well as screw them.

4. Yeah, as long as the arch can provide the fire rating needed you can get an acceptable elevator shaft. About the biggest problem will be the penetrations where the rails go through the firewall to bolt onto your LVLs. This can be an issue which I never 100% resolved (I also wasn't in charge of the fire protection design).

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[Brad805]

The biggest problem with a wood shaft is keeping the lift in spec. We have one supplier that refuses to install their elevators in a wood shaft because of the problems in the first years as the wood shrinks.

 

[TehMightyEngineer]

That's a good point brad and why I used LVLs for the structure in my project. Also, it was installed in an existing building being renovated so the existing floor structures were already at their "shrunken" locations.

Thankfully njlutzwe is going to use LVLs and metal studs so hopefully his shrinkage effects will also be minimized.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[Brad805]

Did you use LVL for all the top/bottom plates in the walls? Most never want to do that, and that is where the shrinkage problems occur. LVL around the shaft is pretty much standard because we all use engineered floor products.

 

[TehMightyEngineer]

I did not and you're probably right that I should have. However, I would suspect that sill plate shrinkage would be within the elevator rail tolerances as it should only cause the rail to move vertically.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[mike20793]

I've done wood stair shafts out of solid sawn lumber without any problems. All the elevator shafts I've seen had all engineered wood assemblies because of the shrinkage concerns Brad expressed. I agree, it is pretty much standard.

 

[Brad805]

LVL top/bottom plates would add quite a lot to the wood package because it would only make sense if all the walls were built this way. One would need a unique client before specifying this. I am not a fan of wood shafts, but I too have seen many built with wood shafts.

 

[Guastavino]

Just to clarify. The arch has specified steel stud walls that run the full height of the shaft. They are NOT structural studs, or at least I don't think they are. I'm not sure if additional rails are needed midway between floors yet. If so, I'll have to provide LVL "columns" to take that load. I plan to let them attach through the 2.5" steel stud wall to the LVL's on the other side. I don't know how they are going to do that yet. The arch is just showing the plans as I posted above. they don't have any details showing anything else. But ultimately, their 2.5" steel stud shaft walls will be tied off at the floor levels somehow. That detail is not in my scope, but may impact me, because I'm guessing that they can't tie the rails to those shaft studs. I'm guessing they are going to have to extend their support THRU their 2.5" steel stud shaft wall.

Here's what I have shown now. A floor opening equal to the elevator shaft + width of the steel shaft wall studs. LVLs installed tight to that. I don't know how they will connect through the shaft wall yet. I'm sure it's possible, otherwise no one would manufacturer these shaft wall studs. I need to keep digging.

 

[Brad805]

Is this the unit?

https://www.thyssenkruppelevator.com/drawings/PDF/S35COTWIN1.PDF

 

[mike20793]

I think you could get by doing just the shafts out of engineered lumber. The elevator openings can be oversized and grouted after the fact and the sills can be adjusted after adjacent shrinkage has occurred. This is how we handle shrinkage around masonry shafts.

 

[Guastavino]

@Brad805,

Yes I think that's it. I don't have project specific info yet. Just general info.

 

[XR250]

The arch has specified steel stud walls that run the full height of the shaft. They are NOT structural studs, or at least I don't think they are.

Never seen shaftwall studs that were structural.

 

[Guastavino]

@XR250, Yea, I think the attachment has to happen at the floors (and if they need an intermediate location, I'll have to figure that out as I go).

Also, they want a CMU pit instead of concrete. I don't see why not (grouted solid and reinforced of course), other than the waterproofing/waterstop detail. But then again, I've never seen a pit out of CMU. Anyone done a PIT out of CMU?

Thanks,

Nick

 

[TehMightyEngineer]

I don't see how it will be any different than a CMU residential basement.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[Guastavino]

Good point Teh. I googled CMU elevator pit and looked around and didn't find anything. I hate reinventing the wheel on things, because I often can realize later I have blind spots. And I don't want in two months to say "OH that's why no one uses CMU. Frankly, my guess, is because it's odd dimensions and involves multiple trades. But this contractor is adamant about CMU.