Mounting a lift on sub-par base

[bmxdad]

I might have access to a Nessbaum 2 post lift, but only have a 4" pad coming in.

I'm a journey level machinist and I used to setup work cells. If a machine was to big for the concrete, we would lay a 1/2" or bigger steel plate and actually bolt it the the concrete. We would then mount the machine to the plate. Never any issues with vibration, cracking or movement. Then again, the average thickness was 8" - 10" inches.

Anyone try this? Maybe getting some 3/8" plate and doubling the lifts footprint.

 

[RVDan]

I have a friend who has his two post that's not even bolted to the floor because he never planned for a lift and put radiant heat in the floor. It's tied to the roof to keep it from going anywhere. So far so good.

 

[Cjk]

My Bendpak only calls for 4" concrete.

 

[sands35]

Drill a test hole where you want to put the lift to see the actual thickness of the slab. Specing a 4" slab might get you 3" or 5" - with some variation.

Worst case you need to cut out some of the concrete and do a new pour under the lift.

You can put down a bigger plate, but that may end of costing more than re-doing the spot under the lift.

 

[evildky]

I don't think the 4" depth is to accommodate the load which your plate would solve. I think the 4" requirement has more to do with torsional load. I've seen some lifts with a couple feet of 1/2 angle coming off both sides which would help this. Not sure if it would be enough.

 

[c4cruiser]

Drill a test hole where you want to put the lift to see the actual thickness of the slab. Specing a 4" slab might get you 3" or 5" - with some variation.

Worst case you need to cut out some of the concrete and do a new pour under the lift.

You can put down a bigger plate, but that may end of costing more than re-doing the spot under the lift.

When I installed my MaxJax 2-post lift, I drilled a couple of test holes to make sure that the garage floor thickness matched the 4" thickness spec on my plans. Turned out that both holes showed only 2-1/2" thickness In addition, there were some minor cracks in the area where I wanted to locate the posts.

I didn't feel that was suitable so I had a local company cut out two 4'x4' chunks and pour new pads that were 12" thick using a 5000 psi mix and rebar to tie the existing slab into the new pads. I used 8" epoxy anchors instead of the supplied 4" expansion anchors. Overkill? Maybe, but I wanted to make sure that there would be no problems with the lift posts/anchors coming loose.

 

[Scud67]

You could always use something like this:
http://www.gregsmithequipment.com/Atlas-Baseplate-Extension-Kit

 

[bmxdad]

Interesting ... kind of the same idea, except the column would be sitting on the plate.

 

[DpSyChO]

Something similar:
http://www.garagejournal.com/forum/showthread.php?p=4048039#post4048039

A local garge has a lift (not positive of brand), that has angle welded to the column and coming out like baseplate extensions on the above link.
The welded angle I believe was factory.
The next time I go to get a vehicle inspected I'll check it out again.

 

[wssix99]

I have a friend who has his two post that's not even bolted to the floor because he never planned for a lift and put radiant heat in the floor. It's tied to the roof to keep it from going anywhere. So far so good.

Wow. I hope you don't stand under it! You might also start his Darwin Award application now. (This would be a shoe-in.)

I think the 4" requirement has more to do with torsional load.

The thickness spreads out the vertical bearing force across the slab and the base under the slab and, on a 2 post lift, it adds moment bearing capacity for the tendency for the lift to top over. (Once the 2 post lift is bolted to the floor, the lift and the floor make an upside-down "T" that resists tipping of the load.


I like that link from Greg Smith Equipment. That looks to be a very clever way to solve the tipping problem. (Bearing capacity shouldn't be as much of a concern.)

 

[Todd.Brock]

I had a Nussbaum SPL8000. I will see if I have the manual , but I not sure it called for much more than 4 ". Not sure what lift you have exactly. JMC equipment in minnehsohta is the go to place for parts and service questions. Be happy to answer any specifics


Edit. Here is the manual for my lift. It says on page 10 that concrete is 200mm, that's 7.8 inches. Unless I'm reading that wrong.
http://www.jmc-autoequip.com/manuals/SPL8000.pdf

I don't know what lift you are looking at, but these were more common in dealerships, etc. It is an 8000 lb asymmetric design. Hope that helps

 

[bmxdad]

Asymmetric ... that's when they have one pair of arms longer then the other. Is it just to allow entry to the car or is there more to it then that ...

 

[gungatim]

my two post came with large angle iron extentions bolted to it. I thought the dealership I got it from added them, but found they are optional from the factory for just that purpose. My slab is around 4", and I make sure to keep any vehicle I lift with the weight centered as close to the lift as possible. theoretically, there shouldn't be any tendency to tip that way.

 

[mikec35]

I have a friend who has his two post that's not even bolted to the floor because he never planned for a lift and put radiant heat in the floor. It's tied to the roof to keep it from going anywhere. So far so good.

Not that I would advocate this at all but the vendor that installed my lift said that he was at a trade show and they had a car on a 2 post lift that was not bolted to the floor.

 

[Todd.Brock]

It scary how easily those posts can be "walked" around when they are standing up. I suppose if the car was balanced just right, but an asymmetric lift biases weight to the rear. And yes, Bmxdad, you are correct

 

[bmxdad]

Well, he sold it to someone else ... bummer.

Besides the MaxJax, are there any other "Short" lifts?
Are the medium lift scissor jacks assessable from underneath?

 

[sz0k30]

I have had an Aresco #9000 lb, 2 post lift in my pole barn for over 10 years. Its on a standard 4" pour. Never had an issue.

 

[theoldwizard1]

I didn't feel that was suitable so I had a local company cut out two 4'x4' chunks and pour new pads that were 12" thick using a 5000 psi mix and rebar to tie the existing slab into the new pads. I used 8" epoxy anchors instead of the supplied 4" expansion anchors. Overkill? Maybe, but I wanted to make sure that there would be no problems with the lift posts/anchors coming loose.

THIS ^^^^

You can cut the concrete yourself with the proper saw blade. It makes a lot of dust and will require multiple passes to get through.

Personally, I would never install a lift on anything less than 6" of concrete.

 

[BDAZSVT]

I cut my floor like and repoured the lift area. I have a friend that had a crack develop under his 2 post and the installers put the post on a large sheet of 1/2 steel. Only thing I didn't like was it tended to be a trip hazard on the plate.

 

[bmxdad]

I have had an Aresco #9000 lb, 2 post lift in my pole barn for over 10 years. Its on a standard 4" pour. Never had an issue.

With all the reading I've done it seems that a lot has to do with how the base is prepared.

 

[ph1gering]

it depends on a lot of things... Thinkness, concrete psi, Base compaction, rebar?

I went with 4-5" pad, with rebar in the entire floor 2' apart, 8" of compacted stone and 5000psi fibermesh concrete. all that adds up to a stronger floor.. Even still when I finally pull the trigger i am going to do some test drills to find the best spot with the correct thickness.

 

[wssix99]

With all the reading I've done it seems that a lot has to do with how the base is prepared.

For a floating slab, it shouldn't matter. The base will see approximately the same pressures with a 2 post lift on top of it as it does with a car parked directly on the slab. (The base plate of the lift distributes the forces similarly to how the contact patches of the tires do.)

it depends on a lot of things... Thinkness, concrete psi, Base compaction, rebar?

I went with 4-5" pad, with rebar in the entire floor 2' apart, 8" of compacted stone and 5000psi fibermesh concrete. all that adds up to a stronger floor.. Even still when I finally pull the trigger i am going to do some test drills to find the best spot with the correct thickness.

Depending on your control joint spacing, you probably have a very good combo. However, the factors above do not directly add up to goodness - the higher PSI concrete can make for a weaker floor as far as a lift is concerned:

The steel in the floor generally helps control cracking of the floor. (As the control joints and expansion joints do.) The lift only transfers a small amount of compressive loads to the floor, so even 3000 PSI concrete will be more than adequate. Cracking is the enemy. The higher PSI concrete has a higher cement ratio, which means greater shrinkage stresses in the floor, which taxes the rebar more. All things equal, (except for the cement compressive strength) a 4000 PSI floor will be less likely to crack than a 5000 psi one.


That being said, reinforced concrete can be a complex material do deal with and there are no absolutes. The steel in the floor can help resist cracking due to bending stresses, however for a 5", 5000 PSI floor with #4 60ksi bar, you'd need to go with a 7-8" spacing to get that effect.

 

[bmxdad]

I'm getting 4" min. of "5 sack or equivalent design mix" with fiber-mix and zip strips. I understand the zip strips and fiber-mix, but 5 sack? What is that?