Car lift post foundation

[hoshang]

Hi all,
I'm planning on using combined RC footing for 2-post car lift of rated load of 4000kg. Do you recommend slab-on-grade 150mm thick with WWR, or my combined RC footing is more convenient? Also, is single column footing with pedestal is applicable?

 

[TLHS]

Not enough information. Footings are pretty much always more comfortable as an engineer, though.

 

[hoshang]

What information do you need?

 

[XR250]

Good question. The lift manufacturers usually give recommendations on foundation but I think they suck personally. Many allow 4" slabs. I have a 2 post lift in my garage and I used 36x36x12" footings doweled into the surrounding slab.
I'm not sure how you would do an actual calc. Assume a 9k vehicle with CG located. some distance from the post center? That would give your front-to-back moment.
Also, some lifts do not have a top crossbar so you have a moment trying to the rotate the posts inwards towards each other. Like this failure on a 2" slab...

 

[hoshang]

XR250 said: Assume a 9k vehicle with CG located. some distance from the post center? That would give your front-to-back moment.​

how one can find the center of gravity of a vehicle?

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XR250 said: Also, some lifts do not have a top crossbar so you have a moment trying to the rotate the posts inwards towards each other. Like this failure on a 2" slab...​

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Is it ok to thicken the foundation to overcome this?​

 

[TRAK.Structural]

You could request from the client to give some guidance on what types of vehicles the lift will be used for, and then do some of your own research on center of gravity.

I think thickened slab areas under the posts could work, but I would detail actual rebar (not wwf) in these areas. Breakout of the post anchors is another problem with these that you should be considering.

 

[hoshang]

Hi all,
should one consider earthquake loads for this type of structure? If so, which section of the ASCE?

 

[rb1957]

I think if you have an earthquake when you've got a vehicle on the hoist, then you've got bigger problems !
You may have some WorkPlace Safety regulations ...

"Surely" calculating the moment on the base is "easy" ? 1/2 the weight of the vehicle (what vehicle ? pick one ... F150 truck, 3000 lbs?) assume load 1/3 the length of the hoist arm (or 2ft or something). Then design the foundation for this moment (and avoid the rather memorable picture above).

 

[EdStainless]

Have a friend with a couple of lifts, a 2 post and a 4 post.
When he built the garage he had beams built into the slab.
The slab is all 5-6" thick and the beams are 10-12" deep and 16" wide (bucket width).
There is a little steel in the beams.
I believe that it is just a couple of bars top and bottom.
He uses them often for over 20 years now without any issues.
Knowing him the anchoring is very deep also.

 

[hawkaz]

Seismic is a very real concern. The footing for these lifts can get thick in high seismic locations due to the bolt requirements
Obviously, you can't predict when an earthquake will hit- so there is a significant risk that the car can be in the elevated position when it occurs. The lift vendors have seismic baseplates for this very reason. They also list the COM location on their cut sheets.

 

[XR250]

I have previously gone down the rabbit hole of trying to get some design guidance form the ALI (american lift institute). No luck there. Maybe things have changed.