Wood Hoist Beam

[phamENG]

Working on a low rise (3 story) multifamily project, and the elevator shaft is to be all wood framed with shaftwall, etc. Doing some reading to refresh myself on the topic, I came across this gem from WoodWorks.

In it, they float the idea (and provide a picture to prove it's been done before) of using a wood hoist beam. Neat idea - makes the connections easier and eliminates a trade from the project (it's the ONLY piece of steel needed). What are the downsides?

I can think of one - if a steel cable is used, it could create some very high localized stresses on the beam that the wood might not like. Anybody agree, or would this not be as much of a problem as I'm thinking? Anything other reasons this should be avoided other than it's not the normal way of doing things?

 

[jayrod12]

Get confirmation from the AHJ. Locally here I did a solid stud (i.e. 2x6@1.5" o/c) shaft for a 1 storey lift. They made them cover the inside with type X drywall and mandated that the hoist beam be wrapped as well. Even though the lift stayed within the same fire compartment of the building. In the end they went ahead with drywalling everything just so the AHJ would get off their back. The client wanted the look of the solid studs on the outside of the shaft so they were pleased in the end. But the drywall on the hoist beam got destroyed when the lift was installed, and I doubt it was ever repaired.

 

[phamENG]

Thanks, jayrod. Good lesson learned there. Got the preliminary elevator cut sheets and noticed that Otis specifically says "steel hoist beam" in their notes, so it may be a moot point. Even so, it's an interesting idea and I could see it coming up again if wood prices ever come back down.

 

[Enable]

I wouldn't necessarily be adverse to the idea though I don't think a steel hoist beam is all that much additional work. It's simple enough that any miscellaneous fabricator could handle it.

Off the top of my head things I would want to think about specific to a wood hoist beam:
1. Fire rating requirements (as Jayrod points out this well depend on local building authority)
2. Creep and deflection. Confirm with elevator manufacturer allowable tolerances (matching floor elevations may be an issue if too much creep)
3. Local stress concentrations as you note. May want to add a reinforcing plate around hoist location to mitigate this
4. Rotational restraint at connections may be hard to provide depending on shaft wall / ceiling configuration

Can't really think of anything else.

 

[phamENG]

Thanks, Enable.

To clarify, this is a hoist beam in a shaft for a low rise hydraulic elevator. So creep and deflection aren't too critical, unlike traction sheave beams with the peculiar deflection limit of L/1666. It gets used to install the elevator, and then pull out the car and put a new one in if it ever has to be replaced.