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 Post subject: Car lift install
PostPosted: December 2, 2019, 11:21 pm 
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Location: Denver Co
So I am getting around to installing my C-7000 car lift and found out that my floor is only 3.5" (actually less that that) where the lift will go which isn't thick enough. So I decided it would be best to pour a new pad. I figured a 5000psi 28" x 28" x 12" deep with a 6" under cut (to tie it back to the existing slab somewhat) would be best. But is it? After looking around online I am seeing everything from 2ft x 2ft to 4ft x 11.5ft requirements will all sorts of thicknesses. Any one have any real thoughts?? I'm not even sure how to calculate the required overturn moments so they I can figure out how much the concrete needs to weigh... I'm not a civil or structural guy. I feel like my size will not be a problem for the race car but at some point I know I'm going to put my Explorer on it and be worried.

Here is the hole :D
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 Post subject: Re: Car lift install
PostPosted: December 3, 2019, 2:21 pm 
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Joined: November 13, 2009, 9:31 pm
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Location: Connecticut
Not a licensed PE, so take this with a grain of salt...

I would make a continuous pad between the two posts, this would take care of the lateral tipping concern, and then make it long enough to go past the center of gravity of anything you would lift to eliminate that concern. I would pour it at least 6" thick with rebar ~2" up from the bottom.

This goes along with what I found online:
Q: How large "stand alone" concrete pad is needed for an
outdoor lift?

A: 2-post lift:
The concrete should be twice the required thickness of a "normal" concrete
floor for the lift's weight capacity. The "slab" should extend at least 24
inches past the outside of each column (side to side) and one foot (front
to back) longer than the end of the extended lift arms when moved to their
"fully extended" position.

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 Post subject: Re: Car lift install
PostPosted: December 3, 2019, 7:33 pm 
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Location: Holden, Alberta, Canada
duratec7 wrote:
Not a licensed PE, so take this with a grain of salt...

Same here

If I were doing this I would sink a 12"-14"diameter x 6'-8' deep concrete piling (using piling tubes) with rebar and hoist tie bolts for each pillar, kinda like what they do for large street lamp posts.

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 Post subject: Re: Car lift install
PostPosted: December 3, 2019, 8:21 pm 
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Geeze Perry, that seams like a much over built design in my un-Licensed PE opinion. It is ~700# to 1350# of concrete per slab/piling. I was thinking of just driving a few steel rods down a few feet before pouring the concrete. I think 8"-9" dia x 42 inches deep pilings are common for deck supports around here. The depth varies depending on the depth of the frost line. I don't pretend to know myself. Mjalaly, what do the instructions of your lift say is needed? Certainly it is specified somewhere in the installation instructions.

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 Post subject: Re: Car lift install
PostPosted: December 3, 2019, 9:32 pm 
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rx7locost wrote:
Mjalaly, what do the instructions of your lift say is needed? Certainly it is specified somewhere in the installation instructions.


The instructions are garbage. Even the vendor was no help. They just told me the manual says 4" thickness but that's the thickness requirement for an existing floor... mine isn't 4". I have been reading more on the web and it looks like quite a few people reccomend a 4ft x 4ft pad 12" deep.

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 Post subject: Re: Car lift install
PostPosted: December 3, 2019, 10:29 pm 
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The requirement for Bendpak 10,000 lift is:
Quote:
https://www.bendpak.com/XPR-10-Series-T ... endPak.pdf

• Concrete specifications. Make sure the concrete is at least 4.25 inches thick, 3,000 PSI, and cured for a minimum of 28 days. Do not install the Lift on cracked or defective concrete. Anchor Bolts must be more than 6 inches from cracks in the concrete or from a wall.


I would trust Bendpak's requirements. They are well respected. Interpreting your situation based on the Bendpak instructions, a min of 6" beyond the bolt pattern of the lift would be appropriate for the cut. 6 inches beyond the base outline would be better with some margin for error. Dig out 4-1/4 inches below the bottom of the existing concrete. Extend the hole under the existing concrete the same 4-1/4 inches on all 4 sides. That would give you the min thickness for the new concrete under the old with a 45 degree angle of "locking" under the old. I would also wash the underside of the old concrete and spray with concrete bonding adhesive to enhance adhesion. not to mention the previously mentioned reinforcement steel. I would check that the crushed stone base under the concrete is still enough since you are digging out deeper than the original excavation and possibly the underfill.

And wait 28 days for the concrete to cure before drilling and installing the anchor bolts.

So the safety factors are:
1) Sackrete and Quikrete found at the home stores are typically 4000 PSI, Higher PSI can be found.
2) You are using a 7000# lift. The above instructions are for a 10,000# lift
3) Cut 6" beyond the base vs 6" from the anchor bolts
4) The Bendpak lifts are ALI certified. I assume that includes the min installation requirements.

YMMV of course and I have no expertise in these matters. But I would not be concerned if I were installing a 7,000# lift using the above guidelines.

Don't come after me if things don't work out for you using these guidelines. :mrgreen:

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 Post subject: Re: Car lift install
PostPosted: December 3, 2019, 10:41 pm 
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Bendpak actually specs out something extreme. Pretty much a gigantic pad with a 6in undercut 12" deep

https://www.bendpak.com/car-lifts/concr ... uirements/

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 Post subject: Re: Car lift install
PostPosted: December 4, 2019, 12:59 pm 
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My Bad! Ignore my earlier posts. :cheers:

It makes sense to me now why Bendpak wants a continuous pour from one post to the other. 2-post lifts do not take a pure vertical load like a 4-post lift does.

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 Post subject: Re: Car lift install
PostPosted: December 7, 2019, 7:03 am 
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IMH and amateur O, for balancing 10,000 lbs on two six foot pillars with a sqft base, I would augment the loading pads with four 1/4x5x5 base plates, ten feet from the upright, bolted to studs epoxied into the floor, then fit threaded rod with a turnbuckle adjustment for tension loads to keep the pillar vertical and help prevent concrete cracking that would require a repour.

Think about an inverted truss (warren,pratt, etc). With trusses, there would be no need for extra thick concrete since the load would be spread over a much larger area. With a long enough truss there would be no need to bolt it down.

Consider what the dynamic load would be if one of the outriggers was not placed properly under a frame rail and a vehicle like a truck with bad weight distribution slipped. Take a look at youtube vids of vehicles falling off lifts.

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