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4 post lift floor requirements

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mrshanes

Member
Joined
Jun 10, 2011
Messages
5
Location
Morgantown, WV
I would like everyone's opinion on my situation. My detached garage has a basement with an apartment above (half story). So, vehicles pull in on the main level with an open basement below. The main garage floor is poured concrete on composite q-decking with steel beam support. At it's thickest, the concrete is only 4 inches. It's a 3 car garage and supports vehicle weight just fine. I'm interesting in putting a free-standing 4 post support. Most specs I see say the concrete should be AT LEAST 4 inches think. In my eyes, having the vehicle weight on 4 posts resting on the floor is no different than having the vehicle weight on 4 tires resting on the floor. It's basically the same minus the weight of the lift itself (which isn't much). Does it sound OK for me to have a lift on this elevated floor? Any one else have this situation?
thanks,
Shane
 
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pmiranda

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Jul 15, 2008
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1,504
Location
Austin, TX
mrshanes said:
In my eyes, having the vehicle weight on 4 posts resting on the floor is no different than having the vehicle weight on 4 tires resting on the floor.
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The lift could have smaller feet than the contact patch of a tire.
(Also a tire is pliant so it will spread the load more uniformly than a rigid steel plate on a possibly uneven floor, but then you could just put rubber pads under the lift feet to eliminate that potential floor-cracking issue.)

I'd bet it will work but I'd want to get a second opinion from the lift manufacturer and check the size of its feet.
 
R

roscoe2000

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Sep 22, 2009
Messages
264
Location
Seat Pleasant Md
A lot of 4 post lift owners used them for storage as well are vehicle maintenance. With that in mind your slab would need to be rated to hold two vehicles in the place of one. Even though you may not plan on using it as such, there is that possibility that it would be used for storage. An A&E would be able to do a structural load analysis, but i suspect that some beam reinforcement will be needed.
 
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ms fowler

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Jun 27, 2012
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450
Location
Littlestown, PA _ 6 miles south of Gettysburg
How much do you think the load on a floor is? What is the tire pressure? Say 35 psi---that is how much load the tire can transmit to the floor or the road. 35 pounds for each square inch of contact area. IOW, the load of a car on a concrete slab is negligible.
For the 4 post lift add the weight of the lift to the rated capacity of the lift and divide by 4--that will get you the max load for each column. Divide that load by the area of the base plate and you will see the max load that the lift and vehicle can impose. They demonstrate BackYard buddies on grass fields at car shows and flea markets.
If the slab is bearing directly on the stone base, the load is transmitted thru the concrete to the stone base. The only problem comes if the stone base has settled and there is a gap between the bottom of the slab and the soil. In that case the concrete will have to resist the shear forces. You can drill a pilot hole thru the slab to investigate of the base has settled.
Concrete slabs almost always weight more by themselves than any load that will be imposed on it.
 
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tgj7

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Dec 1, 2015
Messages
54
The base at each foot of the lift is greater then the foot print of your tires, but you also have to add in the weight of the lift, +1500Lb. In addition add the weight of the 2nd car under the lift.

Also, take into consideration the fact that the fully loaded lift may drop onto its lock if a cable breaks. The force that the impact makes is far greater, think of a hammer.

That said if I can bolt down the lift, and place posts, with a concrete base, in the basement under the lift, I would do it.
 
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Ironcrow

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Sep 30, 2005
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1,169
Location
Arizona
Building codes can vary. There are local ordinances that can supersede or add to codes. The building may not be built to code.

That said, typical floor live loads for a garage are 40 or 50 lbs/ft. 200 square feet of truck parked on a 40 psi floor is a 8,000 lb truck. Punching through the floor with "point" loads, I've seen numbers between 2250 and 3000 pounds per tire sized spot. I might stick a rubber pad under each column to distribute really pointy loads. Make the floor think the column base is a tire.

Seems like two 3000 lb cars and 1500 lb lift would be under "code like" limits.
 
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firworks

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Jun 29, 2015
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IL
coldh2o said:
You all missed the point that this is a suspended slab.
Click to expand...

Cut a hole, pour a concrete block in a form, and suspend it from the ceiling! Might need to cut a hole in the ceiling though to pour some concrete up there too to support the cables to support the floor below.
 
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Pwrgeek

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Oct 18, 2015
Messages
288
Location
Texas USA
I'd get an enigineer to look at it. Depending on when it was built the slab could have been designed for anywhere between 50 and 200 lbs/ft2 of live load. At 50 you're screwed no way you're going to put two cars in one space. At 200 you're golden no problem at all. A structural engineer will be able to tell right away. As for using a four post for a single car with no second car underneath you're fine. The slab will be designed for load distribution (it's probably got tension cables in it to do this) and will do just fine bridging out the load from the posts onto the supports below.


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