Question for the engineers, 2 post lift installation

[pumalex]

Here is my dilemma, the minimum request for a 2 post lift installation is 4" of concrete with 3000 PSI rating. This is what i have, but not more. I wish i was safer so i read everywhere i need to cut the concrete on a 4'x4' square and pour a thicker slab. Thing is, my concrete is brand new and i did not think about having a thicker part for a lift since i didn't think of installing one until now.

Now from what i see, the column base on all those lifts is usually like 15" x18". What if you were to put some wider column base something like 36" and bolt it at the end, that would give a lot more leverage and make the lift much more stable.

here is a picture of a lift, from what i understand, the danger is that if the weight is not well centered, it could try to tilt forward or backward (red arrows). Now if i was to put some longer base (black thing) would that help? Something like a 18" wide by 36" long 1" thick piece of steel that would be bolted to each end in the concrete as well as bolted with the orignial holes of the base column and i would probably on top of that weld the base to the new piece of steel.

Anyone see a problem with that? Would that make the thing stronger and be the equivalent of a say 6" of stronger concrete? Am i completly off and that is not going to do any good to the strenght of my thing?

thanks a lot for any advice.

 

[BillK]

Puma,
The people you need to be asking this question to is the lift manufacturers. I think most of them offer a kit for exactly the situation you have. Unless someone here actually sells lifts or is a LFI member, we would just be guessing. Start here for suggestions http://www.autolift.org/

 

[nehog]

I'd strongly suggest you contact Rotary (if you are installing a rotary lift) and ask them. They will ask the 'right' questions of you, and know the stresses and pressures that develop when their lift is in use.

For example, I don't think just throwing a steel plate on the floor under the lift column will help much, I think you'd have to weld it to the base-plate of the column to get the best results. But I could (easily) be wrong on that.

 

[slopecarver]

Gusset it too but then again i have zero experience and an barely not a mechanical engineer.

 

[ddawg16]

I think you have the right idea. But, like Bill said...see if they sell something....otherwise, a 1/2" plate would certainly spread the load.

But, what you need to take into account is the pitch loading....if you had a 6000 lb car perfectly balanced on the lift...and assumed the feet of the lift was 15x18....then you are only putting a little over 11 lbs/sq in of force on the floor.

Now...remember, your 3000 PSI concrete is actually 20.8333 lb/ sq in.

Remember your physics? Leverage? If that load gets off balanced, you could quickly exceed 20 lbs/sq ft.

If you do add a large plate, it will need some type of gusset to make sure it does not flex. If it does flex, then all the point loading will end up at the point of flex. Concrete is a non-compressable material...it does not give...it just breaks.

This is one of the reasons you will typically see large machinery installed with the feet sitting on bolts in the concrete with about 1-2" of space underneath. Once everything is in the right place, they stuff grout under the plate. The load is not evenly distrubuted into the concrete.

 

[SteelArt]

If they say 4" at 3000psi is fine then I would suggest that anything you do in relation to increasing the foot print will be fine as it will only make it better. Just remember that a flat plate even at 1/2" is going to try and flex so I would be adding a gusset or two along the sides. Even if you groove your concrete sat 1/2" and laminate a side plate on at 90 degrees it will make a hell of a difference.
Most of the lifts we see down here have a length of angle arond 2ft long on the side of the hoist as well as the base plate. This helps a significant amount.

Just remember not to put your bolts to close togeather and the a lot of the requiremnet with the concrete is to do with the bolts pulling out as opposed to the foot sinking in.

 

[pumalex]

hmm this is interesting, i am not really afraid of the lift sinking but more of the concrete tearing up if unbalanced. Not really afraid of the bolts coming out because i will be using epoxy for the bolts instead of those mechanical anchor thing. My guy said he poured 4" but what if it is 3,5"...

As far as the plate under the base, i was more talking about a 1" thick plate rather than 1/2" but i admit that the angle iron (let say 1/2 or 3/8 thick and 3"x3" for example) would be stronger. I beleive the way it is made in the pic seems like a good idea to give some stability, anyone else has some opinions on that picture?

thanks a lot everyone, didn't think i would get so many relevant answer so quick.

 

[jkeyser14]

Call the company and ask them. It's your life and your cars at risk, take 10 minutes and talk to the real product engineer, not a bunch of people on a forum who will give you their uneducated opinion. No offense anyone, but if you don't know the physics and stresses involved you should not tell him to do something that could put his life in jeopardy.

 

[DHS]

I doubt that you will get any answer other than to follow installation instructions provided, just to cover their asses.

 

[pumalex]

i tend to agree, i really doubt they have a concrete or mechanical engineer that can answer my questions. An the team of engineer that designed the thing are probably not working there anymore, it's designed, wht keep the designer? I am sure all i'll get for answer is pour a new concrete.

I will certainly give it a shot though, that is for sure but having other people opinions might be good, someone could tell me that it is dangerous for some reason or completly useless for a reason i didn't think of.

 

[DHS]

I too have 4" concrete (maybe 3" for all I know) and though of bracing from the top of the lift to a steel beam overhead.

 

[WNYflyer]

Additional large plate of a proper thickness will reduce the uplift in the bolts due to the greater spread on the bolts.

If that strut across the top is not considered a structural member then the requirements for the amount of weight and spread of the concrete engaged by the base plate and bolts will not be significantly changed by the addition of the large plates.

If the strut is structural then a lot different scenario but I would suspect you would still have a problem.

Still need to worry about the location of your concrete slab control joints relative to the bases.

As others have said talk to tech support and get the real story/requirements. Most of the concrete requirements that I have seen on the websites are too vague. You need to know the "real" concrete requirements for the lift you are looking at before you do anything.

 

[Alaric.H]

I use a low ceiling lift at my house and you only need 4in slab for them bot there is a ramp in the middle.

 

[Ironcrow]

Now if i was to put some longer base (black thing) would that help? Something like a 18" wide by 36" long 1" thick piece of steel that would be bolted to each end in the concrete as well as bolted with the orignial holes of the base column and i would probably on top of that weld the base to the new piece of steel.

Yes, this is a great idea and will solve your problem. The bar across the top of the lift will prevent the columns from tipping inward. The larger base will increase stability and reduce the stress on the concrete. Your instinctive dimensions are close to right. I'd go with 3 or 4 feet long and gusset to the columns. Consider something on the order of 6 inch by 6 inch angle about 1/2 inch thick. The vertical leg of the angle iron will serve as a gusset so the 3 foot long piece will not bend. I'd weld it to the outside of the column and put a few mounting holes along its length to shoot it to the floor.

 

[JOHNMAN]

i tend to agree, i really doubt they have a concrete or mechanical engineer that can answer my questions. An the team of engineer that designed the thing are probably not working there anymore, it's designed, wht keep the designer? I am sure all i'll get for answer is pour a new concrete.

I will certainly give it a shot though, that is for sure but having other people opinions might be good, someone could tell me that it is dangerous for some reason or completly useless for a reason i didn't think of.

I highly doubt that Rotary (a division of Dover) has no Engineers that could answer all of your answers.

When I contacted them for installation instructions and a manual for my old lift, they responded within the day with the proper documentation. They even provided the spec for their recommended anchor bolts.

Where did you buy your Rotary lift? My dad bought the one I have new, but when I installed it in my current garage, I couldn't find the instructions or manual, so I contacted Rotary. They were more than helpful.

I doubt that they would recommend field modifications to the base plate.

I would be more concerned with the anchors holding in your new concrete. If you do install the lift using your current floor, I recommend drilling all the way through the floor for two reasons: 1) you can determine without a doubt how thick the floor is, and 2) you can drive the anchors down into the floor if you should ever remove the lift.

My advice is to follow what Rotary recommends.

 

[Wastedwagesracing]

Not sure if this help you or not. But it's the most complete installation info
I have yet to find.

http://www.mohawklifts.com/consumer/library/Slab_Req-Reco_2-2010.pdf

 

[SteelArt]

I recommend drilling all the way through the floor for two reasons:

If you are going to drill right through the slab then take into account you are now allowing moisture etc to contact your bolts so make sure you use correctly treated hardware.

In relation to getting to talk to an engineer, unless you can provide test results on you slab I doubt they would want to commit to a variation from the approved lines and open themselves up to liability issues.

In relation to a field solution, solutions made while actually looking at, and inspecting the area are going to be much more effective than some dude in an office with a span table guessing the resultant MPA of your concrete. Do you even know what reo was put in and what MPA / Slump your concrete was ? I doubt it so anything will be best test guess.

Every hoist I have ever installed I have added base bars to as if you do the maths you will see the result in even adding an inch or so is well worth the effort.

Anyway I say on 4" with a 300mm base bar you will be fine, add on your 1" plates and you will be safer than factory mounts on 5 or 6 inch ...

 

[SteelArt]

Oh forgot to say if in doubt install the lift and measure under the posts with feeler guages / shims and then see what variation you get when you lift a car and then check it every now and again to see what is happening if in doubt

 

[Shadowdog500]

I doubt any engineer from any lift company would tell a random caller that it was ok for the caller to weld a plate to the bottom of their lift to make it better .

Chris

 

[pumalex]

I use a low ceiling lift at my house and you only need 4in slab for them bot there is a ramp in the middle.

I have not bought the lift yet by the way so i don't own a rotary. I want to make sure i can install it in the garage before i buy it.

Did you install the angle iron yourself or did it come with it?

I will also be installing a low ceiling lift like this.

 

[SteelArt]

All the lifts I have, have angle welded on from factory. It seems they dropped this feature when they went clear floor. I am guessing that it has something to do with the post support and bending moments when you have the line rods at the bottom as opposed to the top.

Welding a plate / angle onto the base of the post can not have any negative input to the operation at all. Unless people are suggesting that the lifts are designed to flex like a hot rivetted 4WD Chassis, which is not the case at as they are seam welded thus no flex is designed in their construction.

Anyway I agree with the comments of others who say never trust what people write on the internet, I could be some random clown with an eBay welder and 4" grinder who calls himself a fabricator. Or I could be an engineer with more than a couple of bits of paper, 20 years experience and a couple of hundred grand of tool in my garden shed, who knows .....

 

[Alaric.H]

I have not bought the lift yet by the way so i don't own a rotary. I want to make sure i can install it in the garage before i buy it.

Did you install the angle iron yourself or did it come with it?

I will also be installing a low ceiling lift like this.

It came with it I picked up this lift on craigslist for 1500 installed.
There are supports under the ramp as well.

 

[Aberdale]

Enlarging the base plates will reduce the stress on the concrete. As mentioned earlier, the plate will need to be gusseted back to the column to reduce bending in the plate under load. This will likely make it more difficult to sweep/clean around the lift, and will be another obstacle to trip over, which is why most lift manufacturers keep the base plates as small and low profile as possible.

No matter what your modification, it will likely void the warranty on your lift, if the modification is not a kit supplied by the manufacturer. It's up to you to decide whether the warranty is valuable to you or not.

Seems to me the more viable solution is to cut out your existing concrete where the lift will go, and repour to the correct thickness. If it were me, I'd sleep better knowing it was installed right.

 

[qwkstang50]

I think you have the right idea. But, like Bill said...see if they sell something....otherwise, a 1/2" plate would certainly spread the load.

But, what you need to take into account is the pitch loading....if you had a 6000 lb car perfectly balanced on the lift...and assumed the feet of the lift was 15x18....then you are only putting a little over 11 lbs/sq in of force on the floor.

Now...remember, your 3000 PSI concrete is actually 20.8333 lb/ sq in.

Remember your physics? Leverage? If that load gets off balanced, you could quickly exceed 20 lbs/sq ft.

If you do add a large plate, it will need some type of gusset to make sure it does not flex. If it does flex, then all the point loading will end up at the point of flex. Concrete is a non-compressable material...it does not give...it just breaks.

This is one of the reasons you will typically see large machinery installed with the feet sitting on bolts in the concrete with about 1-2" of space underneath. Once everything is in the right place, they stuff grout under the plate. The load is not evenly distrubuted into the concrete.

ddawg16 what do you mean 3000 PSI concrete is actually 20.8333 lb/ sq in.? I am confused.

 

[stingry]

I have not bought the lift yet by the way so i don't own a rotary. I want to make sure i can install it in the garage before i buy it.

FOUR post lift-problem solved!! I say this tongue-in-cheek, I have not liked 2 post lifts for the very reason that is being discussed here. People buy them and bolt them to concrete that they know nothing of and hoist cars over their head! And to make matters worse, they (the lift companies) make asymmetrical models that come with a built in off-center moment which works to rip the anchor bolts out of the floor.

Cheers
Steve

 

[pumalex]

i already have a 4 posts lift but i am unable to take out an engine from under the car or work on suspension and wheels. Although that doesn't bother me a lot, pulling a Porsche engine with the car lifted in the air on jack stands isn't really safe either.

Unless someone has a good solution on how tu pull an engine between both ramp of a 4 posts lift, i am all ear.

 

[ddawg16]

ddawg16 what do you mean 3000 PSI concrete is actually 20.8333 lb/ sq in.? I am confused.

Total absolute brain fart on my part.....I've been doing too much PSI to Water Column...vacuum to PSI/Bar....milliBar to Inches....I'm been away from home too long....not getting enough sleep...much less ***......

Yea....what ever the other guys said.....

 

[Daedalus]

That is really overkilling it. 1" thick plate? The lift probably has maybe a 1/2" plate max at its base. And you would certainly have to weld it for it to make a difference. If not, then there's no benefit. Gussets would help reduce stress on the joint of course, but again there's no reason to make them any larger than the ones already on the lift.

Something I think a lot of people miss is that the preload on the anchors is higher than the tension created by the weight of the vehicle. If you can torque up the anchor to the manufacturer's specs, it will hold the vehicle. You ought to be re-torquing prediodically to check for any slippage/faults, and very frequently after initial installation.

Finally, if you put a 1" plate under the lift, it might impact operation. Ground clearance is reduced of course. I already have a difficult time getting my lift under my coupe with about 5" clearance. And on my lift the arm-locks have pins that disengage when they touch the ground. A 1" spacer would mean having to hold the locks with 1 hand while positioning the arm with the other hand...unless the plate was extended to be under the lock pin, or the pin was lengthened an inch.

 

[BillK]

Puma,
One more thought. When we moved into my last location for the shop, there was a Challenger lift installed. We wanted to move it to a different location so I called the Challenger dealer in my area and asked him the best way to do it. When all was said and done, we paid him to move it and install it in its new location. I think he only charged us $300 or so, which was cheap insurance to know that it was done properly. That was a few years ago so I am sure prices have gone up, but why dont you see what Rotary will charge to have the lift installed by thier installer ?

 

[Alaric.H]

Here is a picture of all the mounting points in a low ceiling lift as you can see the load is spread out over a large area. If you look at the middle you can see 4 more anchor bolts.

 

[stingry]

Unless someone has a good solution on how tu pull an engine between both ramp of a 4 posts lift, i am all ear.

Ya got me there!!!

 

[Alaric.H]

i already have a 4 posts lift but i am unable to take out an engine from under the car or work on suspension and wheels. Although that doesn't bother me a lot, pulling a Porsche engine with the car lifted in the air on jack stands isn't really safe either.

Unless someone has a good solution on how tu pull an engine between both ramp of a 4 posts lift, i am all ear.

It seems we are kind of in the same boat.

 

[saabman]

The footprint of the columns is small relative to a modern lift. So the thick and large column base of a modern lift is spreading the force (albeit in a different configuration)

 

[pumalex]

Finally, if you put a 1" plate under the lift, it might impact operation. Ground clearance is reduced of course. I already have a difficult time getting my lift under my coupe with about 5" clearance. And on my lift the arm-locks have pins that disengage when they touch the ground. A 1" spacer would mean having to hold the locks with 1 hand while positioning the arm with the other hand...unless the plate was extended to be under the lock pin, or the pin was lengthened an inch.

hmm see i kind of didn't think about that one, hence why i came and asked on this forum.

 

[pumalex]

Puma,
One more thought. When we moved into my last location for the shop, there was a Challenger lift installed. We wanted to move it to a different location so I called the Challenger dealer in my area and asked him the best way to do it. When all was said and done, we paid him to move it and install it in its new location. I think he only charged us $300 or so, which was cheap insurance to know that it was done properly. That was a few years ago so I am sure prices have gone up, but why dont you see what Rotary will charge to have the lift installed by thier installer ?

I am not in the US, i am in a small city in Quebec Canada, we certainly have no specialist around here and pretty sure that if i need to buy a rotary or bendpak or any of those big brands, i will have to buy it out of province.

 

[Ironcrow]

hmm see i kind of didn't think about that one, hence why i came and asked on this forum.

Yeah that's why I'd "weld angle next to" instead of "perch on top of thick plate"

 

[Tscott]

Just as a point of information, any engineer worth his salt will build in a large safety factor on anything he designs. This includes your floor and the lift itself. Chances are the minimum floor thickness quoted is well over twice as strong as it needs to be to handle the loads imparted by the lift. I would still consult the manufacturer, but I see no reason to add anything to the lift if you have a solid 4" of concrete to work with.

Tom

 

[pumalex]

Just as a point of information, any engineer worth his salt will build in a large safety factor on anything he designs. This includes your floor and the lift itself. Chances are the minimum floor thickness quoted is well over twice as strong as it needs to be to handle the loads imparted by the lift. I would still consult the manufacturer, but I see no reason to add anything to the lift if you have a solid 4" of concrete to work with.

Tom

good point, i also thought of that

 

[brownbagg]

the force is in the pull of the bolts and not the weight or footprint, if the red head does not move then the lift is safe so yes spreading out the bolts will have let force by tilt but the four inches is for the grip of the bolts. 3000 is to keep it from crumbling. the weight of the vehicle is almost nothing.

 

[Ironcrow]

Generally true, but here's the thread where the bolts held and the lift toppled ripping the concrete to pieces:
http://www.garagejournal.com/forum/showthread.php?t=78602