Elevator support design forces

[Taro]

In my experience, elevator support design forces (hoist beam, guide rail, pit slab, etc.) are sometimes difficult to obtain during the design phase. Some elevator suppliers do not want to give out this information before they have a contract to supply the elevator. That leaves the structural engineer with the option of making these items bidder-designed, deferred submittal, or using assumed forces that are verified during the construction phase (possibly necessitating redesign). Have others encountered this situation? Are there resources available for determining reasonably accurate design forces without relying on the elevator supplier?

 

[LPPE]

Typical hoist beams only span 6 or 7 feet, and the service load is usually 5 to 6 kips, and the hoist beam doesnt see nearly that loading for the one-time shot. You can probably get a W8x15 to work, plus it fits into masonry coursing.

 

[Taro]

OK, that's a pretty simple case. But what about sheave beams that might span 30 feet or more with impact loads, allowable design stresses reduced 20%, deflections less than 1/1666 of the span, etc? Not to mention all the other design requirements for the guide rails and pits.

 

[ishvaaag]

Some indefinition exists as well in Spain. Fortunately most cases fall closer to what pylko tells than the big spans of your last post. Here a mat is placed atop the lift hole, and on this motors and pulleys on which the lift hangs. For these "simple" cases, direct design is provided for such flat plates (with a significant number of small holes) in the NTE ITA Ascensores.

The spanish code for Aparatos Elevadores

ITC-MIE-AEM-1

has specifications for minimum loads in slabs at bottom that protect underlying visitable sites (~500 kgf/m2), plus evaluation of vertical forces when breaking a free fall, both in the guides and springs under the counterweight.

There's also a book, I think by

Arizmendi

specially dedicated to lift issues.

Stein & Reynolds indicate that the vendors give the data for structural calculations. Anyway some information there is in their manual on elevators but scarce on this.

see argenitinian link

http://www.construir.com/Edifica/document/cirsoc.htm#Sobrecargas

 

[LPPE]

The guide rails are just that - rails to guide the elevator. They shouldn't be taking any gravity loads. The piston for the elevator (assuming only a few story high elevator) usually is supported by 2 C's which rest on your pit slab. Therefore your pit slab should be designed for the elevator loads.

 

[Taro]

Yes, I know that the guide rails do not take gravity loads. However, if you have tall story heights (say over 14 feet) the manufacturer's standard guide rails may be insufficient and require structural support for lateral forces.

And I know that the pit slab should be designed for the forces. There are also buffer reactions and many other design considerations. That's my point--- sometimes you don't know what the reactions are because the elevator manufacturer won't give the information before they have a contract in hand. Does anyone have any helpful suggestions?

 

[JAE]

Taro: no helpful suggestions but I've never really had a problem getting info from elevator mfr's as they are always too happy to get in on the project before its out for bids. Have you tried many others in your area? They usually put together a quick, approximate cut-sheet showing the rail and sheave beam forces. These are usually pretty close for your design. As in pre-engineered building column loads, we usually factor them up a bit to cover variations in the final design.

 

[Taro]

JAE,
I've usually gotten cut sheets from manufacturers in the past with no problem also. It's only in the last couple years that it has become difficult to get information out of some elevator companies. It has happened on the last couple projects I worked on. I don't really know why. You would think that this is fairly standard information that wouldn't cost them much if anything to provide. Some of the contractors I have worked with have told me that they have experienced the same thing. I agree that it seems like they would want to be as cooperative as possible so that the designers will be more likely to specify their products, but that doesn't seem to be the case lately.

 

[JAE]

Maybe you could ask them (the elevator reps) point blank to understand the trend. I admit, I haven't called on one for a while.

 

[Liftman]

Taro. It is wrong to assume that there are no loads imposed onto the guide rails.

Significant loads are imposed during the testing or operation of the safety devices that prevent the cabin from falling in the very unlikley event that the suspension ropes fail. The safety components that prevent this are designed to bring the elevator cabin to a halt within 1g.

The arrangement of the guide rails is also considered as the pullout values imposed onto the guide fixings are significatly different depending on how the elevator is arranged.

Calculations and examples can be found in the European normative for elevator design EN 81-2