Making a floorplate type 2 post lift more stable

[davejo]

History:

Wanted a lift, found a used one, bought it and installed it in my pole barn. The concrete was about 4 inches thick when I drilled the holes, I don't know the concrete psi rating.

The lift is a knockoff of a Worth 12000 floorplate lift. The manual calls for 4 inches of 3000 psi concrete. The baseplate is massive at 24 inches by 34.

It has ten 3/4 inch Simpson Wedgeit anchors torqued to 150 ft#. According to this table, each anchor is rated at 6760 pounds in tension. The table also show "allowable pounds" of 1690# which gives a 4x safety factor in 2000 psi concrete...

http://www.strongtie.com/products/anchorsystems/mechanical/wedge-all/loads_carbonsteeltension.html

Fuzzy math: By some crude notepad calculations I think I need each anchor to hold 2400 pounds if I load the lift with 12000 pounds. That puts my safety factor at 2.8.

Reading this thread made me think of ways to make the upright lift columns more stable since they have no crossbar over the top to transfer any tipping forces to the opposite upright.
http://www.garagejournal.com/forum/showthread.php?t=314935

I'm thinking of either building a crossbar up high to tie the uprights together or connecting the uprights to the buildings posts with cables. Again crude calculations tell me that there would be 2500 pounds of tipping pressure at the top of the 10 foot uprights when the lift is loaded at its capacity. Two strands of 3/8 cable tied to the walls would give me 4880 pounds of tension capacity if all the anchors in the floor pulled out.

anyone want to check my math?

I think it would take 3 hours to rig cables, 3 days to build a crossbar and 3 months to pour a new concrete base....

 

[Strouty]

So what connects the two uprights? Is it cable, chain, hydraulic? The one I had was attached at the base like a U and had 1 1/2" solid square tube holding it together.

Just so you know regular two post lifts do not have bracing connecting them, it is just to hold the safety stop and equalizing cables or lines. Nothing really structural about it.

 

[gungatim]

I'm no structural engineer, but if both posts are equally loaded, is there really a fulcrum on the inside of the post? Seems the down force would equalize between the two.

my 2-post does have a structural horizontal member which is rated for 1,000 lbs. lift, but that's because there is a trolley option for pulling motors. I haven't seen that on very many lifts in a long time.

I would be more concerned with the fore/aft tip, which is also why mine has optional outriggers on the posts...

curious what others have to say.

 

[pmiranda]

I haven't done calculations like these from scratch in about 20 years but shouldn't you have the distance from the fulcrum point (inside edge of baseplate?) to the column somewhere in there?
Doesn't the inner baseplate carry the static load of whatever you're lifting?

I think the lift column transfers the 6000 pound point load to the ~2 sqft of baseplate to the inside of the column, spreading it out to under 1000psi with the anchors only counteracting tension from the lift bending and dynamic loads... but I could be very wrong.

And that's just the side-to-side forces. If it's an asymmetric lift (or a symmetric lift not in perfect balance) there are front-to-back forces.

(Edited load from 100psi to 1000psi to account for the fact the baseplate is not as long as the lift arm!)

 

[davejo]

I was thinking that the column would try to tip inward over the baseplate toe if the anchors pulled out of the concrete. That is why my fulcrum is placed there. If the concrete collapsed downward, the fulcrum point would move back under the upright in the crater,

Strouty, ill take a picture of my lift but here is a snippet from gregsmithequipment that got me thinking about this:

"The bottom line is that a 10,000 lb. capacity Overhead 2-post model offers better stability than a 10,000 lbs. Baseplate 2-post design because the overhead bar between the vertical columns provides support to the top of both columns when the car is being raised or lowered.

As the vehicle (located between the two columns) is being raised or lowered, a lot of pressure is being transmitted to the (embedded) anchor bolts located on the back (or outside) of the vertical columns’ mounting plates. The Overhead design transmits some of the pressure from the weight of the lifted vehicle from these anchor bolts to the bar between the columns as the vehicle is being raised"

 

[lakeroadster]

Your math looks good enough to me.

If you use the cable method... run some calculations to make sure you don't pull down your building too.

If you do follow through with your plan..... make the cables / cross bar loose so they / it only engages if the anchors start to fail.

I had similar concerns before I installed my lift. Once it was installed and I started using it I haven't had any concerns. Folks tend to overthink stuff, at least I know I do.

Having run numbers on the anchor bolts on my Rotary lift... they are so over designed you'd have to have multiple failures.

What about the lift arms.... and the hydraulic system, and the safety cables, and the welds that hold everything together...... concerned about redundancy for those too?

 

[52wrench]

T is actually less than what you calc'd because of the distance between the post and the fulcrum but it's ok for what you are doing. I would not tie the lift into the structure. I'd build the cross piece at the top of the posts, there is no need to make it loose, it's not going to cause any add'l binding of the carriages than already exists if the posts aren't perfectly parallel.

Edit - I looked at your drawing again. If the 50" is the distance between the lift pad and the fulcrum point than the 2500# is correct.

 

[wssix99]

Reading this thread made me think of ways to make the upright lift columns more stable since they have no crossbar over the top to transfer any tipping forces to the opposite upright.
http://www.garagejournal.com/forum/showthread.php?t=314935

anyone want to check my math?

Your assumptions are way too conservative and you should make sure you don't adopt the flaws in that other thread. ^ (BTW - At the point one needs to add bracing to cross the clear space under a 2 post lift, I'm not sure what the point is in having a 2 post lift!!! Time to go to a 4 post, then.)

The analysis above assumes that the interface between the vehicle and the lift is frictionless slip joint, which is not the case. There are some lateral forces (stabilizing the posts) transferred through the lifting points and through the vehicle. I have NO idea what that force would be in real life - but I'm sure it would be fun to calculate. There are some specialty lifts out there that don't even bolt to the floor. Even though they have longer legs at the bottom, they must have this kind of lateral help to stay upright: (otherwise, they would be on the edge of tipping) http://www.bendpak.com/car-lifts/specialty-lifts/pcl-16hd-6.aspx

Your lifting arms are also much much much less than 50". In real life, they will spread out forward and backwards, so the lever around your fulcrum is shorter. If you end up lifting a vehicle such that you need to extend the arms all the way out to 50", you'd end up with a 4' wide vehicle/garden tractor/etc. and a much lighter load.

In real life conditions, I expect that you will find the forward/aft tipping moment for an off-balanced vehicle to have a higher potential force than what the inward tipping moment would be. (This is the thing that the manufacturer warns about and very directly points out can kill people!)

 

[pmiranda]

Your assumptions are way too conservative and you should make sure you don't adopt the flaws in that other thread.
...
The analysis above assumes that the interface between the vehicle and the lift is frictionless slip joint, which is not the case. There are some lateral forces (stabilizing the posts) transferred through the lifting points and through the vehicle.

I hadn't read that other thread until today but it brings up a great point... the column deflection inward is part of the design. If you try to prevent it, you put outward shear force on ALL the anchor bolts.
That is also why I think the lift design does not depend on any lateral force through the lift points. That and the fact that you can't really count on the friction of the pads so they must be designing without that.

 

[matt_i]

My opinion...it is a crazy idea to attach a cable to a wood framed building and expect it to hold a static load of 2500 lbs in opposing directions. Bad idea. Its not designed for that kind of concentrated side load. Best imo if you are worried is a square tube connecting the tops of columns somehow.

I agree with Wssix99 in that the major concern is fore-aft loading and the potential imbalance in the other plane, 90 degrees away. And that can't be resolved by cables or connector tubes.

In another thread I posted about Sika Anchorfix 2. IIRC the shear strength of the epoxy was around 900 psi with good prep. And you get to use 55% of that due to site conditions. So lets say 450psi. Take the shear area, 3/4in * pi *4" * 450psi. 4200 lbs pullout per epoxy anchor vs. 1600 lbs for a wedge anchor. Now you know why I harp on epoxy anchors despite the extra prep.

Were it me, I'd figure out how to use my magnet drill press and drill out those wedge anchors, or, assuming you drilled completely thru the slab, knock them down into the subgrade and go back with B7 threaded rod from McMaster Carr...its more or less a "grade 5" material.

 

[Strouty]

So the horizontal structure at the base is flimsy? Most baseplate lifts have shorter columns and the movement on a 12k lift should be minimal. If you look at the piece that goes across from post to post on a standard 2 post it is not very structural, it may offer some stability, but if the floor plate ever were to fail, it would just crumple and the post would tip over.

 

[Dragster Racer]

Too many years ago did I do these calcs to be competent currently at them. But off the cuff, I like the spreaders at the top. It takes very little material to be strong enough to stop any fears of inward tipping stress. It is important to TRY to center the CG with the columns. But really there is a lot of guessing that goes on there. Honestly, the concrete makes me a little nervous. That's not me saying you shouldn't do it. It's just in the back of my head. I would not tie into the structure.

 

[davejo]

Thanks to everybody talking me through this.
The floorplates are quite beefy and its true my diagram is worst case scenario on the 50 inch lift-arm distance.

Here's the install, the lift is placed midway between the 6 by 6 posts, ten feet apart. My cable plan was to put two cables on each upright to the posts upstream and down stream which I think would take care of the fore and aft problem as well. (isosceles triangle of upright, post and post)

I need to figure out how much tension one of the posts could withstand, obviously. The walls are 14 feet high....

 

[52wrench]

"Your assumptions are way too conservative and you should make sure you don't adopt the flaws in that other thread. ^ (BTW - At the point one needs to add bracing to cross the clear space under a 2 post lift, I'm not sure what the point is in having a 2 post lift!!! Time to go to a 4 post, then.)"

How many tire rotations have you done on a 4 post w/o having to use add'l jacks?? I'm interested to hear what the flaws are on the other thread?

"I hadn't read that other thread until today but it brings up a great point... the column deflection inward is part of the design. If you try to prevent it, you put outward shear force on ALL the anchor bolts."

That's a new one, totally false. Tieing together the tops of the posts with a beam has no effect on shear force on the bolts. It greatly reduces the tensile force applied to the bolts by the posts wanting to pivot on the inside edge of the base plate and trying to pull the anchors out of the concrete.

 

[brownbagg]

but you are question whether the lift itself is the weak link, when in fact the weak link would be the pull out of the anchor, a car itself weights nothing when compared to the hydraulics cylinders capability. so i would be more incline to focus on anchor bolts than tieing the top together

 

[pmiranda]

Tieing together the tops of the posts with a beam has no effect on shear force on the bolts.

I agree. I was wrong about that.
I haven't seen how to calculate how much of the load would transmit into the cross beam, how much would compress the inner portion of the baseplates against the floor, and how much would tension the outer anchors, but it's a function of how high the load is lifted, the shape of the columns (C section probably?) how they're coupled to the baseplates, and the distances from the column to the anchors.

I can say that the higher you lift, the more force would be placed on the cross beam. If it's too much the cross beam could fail and if it did so suddenly it would place a large dynamic load on the outer anchors and if they weren't strong enough to take the load in the first place they would definitely fail and probably in dramatic fashion.

 

[Strouty]

I guess I am still confused, are you concerned with your concrete not being adequate or the lift itself? If the concrete is junk and you tie the column to the structure when the **** hits the fan, the building will be compromised.

Have you used the lift? If so check the torque on the anchor bolts, if they loosen up then I would be worried, if the concrete is cracking, I would be worried. If none of this is happening and you are seeing flex in the columns, that is normal. Steel is a hard form of rubber, if it doesn't bend it breaks. The design of that lift has a safety factor built in, are you lifting something too heavy? Remember that the design of a two post lift is to have things as balanced as possible. So if you have a 12,000 pound truck and it weights 3000 pounds on the front axle and 9000 pounds on the rear axle, you are overloading the lift. As a 12k lift, it can only take a maximum of 3000 pounds on each arm.

 

[davejo]

Yes my thoughts were to stabilize things to reduce the potential of the anchors pulling out of the floor. I don't doubt the robustness of the lift itself, just the DIY installation. The concrete looks perfect and smooth but I got paranoid when I see other lifts calling for concrete thicknesses way over the 4 inches that I have.

I haven't had a car on it yet as you see I am still too cluttered in there. My f450 is about 9000 pounds empty and is the heaviest thing I own at present.

http://www.autoliftmfg.com/al2-12k-fp.html

 

[52wrench]

Rotary calls for 4 1/4 in. of 3000 psi for their 12000 2-post.

 

[lakeroadster]

I hadn't read that other thread until today but it brings up a great point... the column deflection inward is part of the design. If you try to prevent it, you put outward shear force on ALL the anchor bolts.
...

...That's a new one, totally false. Tieing together the tops of the posts with a beam has no effect on shear force on the bolts. It greatly reduces the tensile force applied to the bolts by the posts wanting to pivot on the inside edge of the base plate and trying to pull the anchors out of the concrete.

Not false at all... This was discussed on your thread...

By forcing the uprights to follow the owner installed cross rail, in the event they are not parallel with each other.

The lift mechanism was designed to be loaded from the weight of the car only, the cross bar, (if rigid) induces lateral thrust loading the lift was never intended to see.

This would put high lateral stresses on the sliding lift mechanism, as well as other parts of the lift, including the anchor bolts.

Take the design to extremes and you will understand my point. Assume the span of the columns are two inches narrower at the top than they are at the bottom. When you lift the vehicle it is trying to spread the rails apart, this induces very high loads on the anchor bolts.

Without the cross bar the arms simply slide on the vehicle frame...but with the cross bar everything is locked solid, which is not the design intent of the lift.

You even changed your original intent, which was to lift the vehicle with the bar installed and admitted it was a good idea to make the cross beam loose to avoid issues.

.... I'm putting the cross bar in place after the vehicle is raised and removing it before it is lowered. There are no dynamics involved whatsoever since nothing is moving with it installed so it is not putting any add'l stresses on the sliders, posts, etc. ...

... the cross post is installed after the vehicle is at the desired height and it is removed before it's lowered... That's how I've decided to use it just to remove any chance of binding even though my posts are absolutely parallel and there is enough play between the tube and collars to handle any difference in lifting rate between posts....

Manufacturers recommend against these kind of alterations for good reason. I am still not understanding why you fellas are changing lifts that don't have issues, when your changes can result in issues. The old adage "if it ain't broke, don't fix it" seems applicable here. And don't say you're making it better.... to make it better there has to be an issue.

 

[Strouty]

If this is about making you comfortable, then I am not going to be too much help. I would put the truck on it and lift it several cycles, check the torque on the anchors, they may loosen a bit as things seat in, but if you have one that keeps loosening then it is not seated or there is an issue with the concrete. I would not over think this until it is an issue. I thought maybe you put a truck on it and the columns looked like bananas or something and you were freaked out. If you are really that concerned then make some extensions and spread out the load.

http://www.gregsmithequipment.com/Atlas-Baseplate-Extension-Kit

 

[52wrench]

in response to lakeroadster,
You are confused. Mine has the cross beam between the carriages and could potentially cause some binding by exerting force on to the carriages IF the posts are not parallel and IF the beam is left in place during lifting or lowering. He is looking at installing a beam between the tops of the posts. It is in no way going to cause any additional stresses on to the posts, anchors, carriages or whatever. There is no way that it can cause additional stresses on the carriages because it is not between the carriages. It simply prevents the top of the posts from tipping together and as such greatly reduces the bending moment applied to the bottom of the post and as a result the tensile force trying to pull the anchors out is also greatly reduced. There is absolutely no need to leave any slop when attaching it to the tops of the posts.

 

[brownbagg]

but the one picture is a low height lift so the crossover going hit cab of truck

 

[52wrench]

for lakeroadster:

First, the posts are installed parallel, Second, the vehicle is not attached to the lifting arms. Think.

 

[srr]

If this is about making you comfortable, then I am not going to be too much help. I would put the truck on it and lift it several cycles, check the torque on the anchors, they may loosen a bit as things seat in, but if you have one that keeps loosening then it is not seated or there is an issue with the concrete. I would not over think this until it is an issue. I thought maybe you put a truck on it and the columns looked like bananas or something and you were freaked out. If you are really that concerned then make some extensions and spread out the load.

http://www.gregsmithequipment.com/Atlas-Baseplate-Extension-Kit

I think these are a great peace of mind addition! My lift is a "Benwil" Outrigger and came with something to this effect. My base is 5" thick.

 

[davejo]

but the one picture is a low height lift so the crossover going hit cab of truck

Yes the floorplate setup was appealing since you can put tall things like sprinter vans on them.

My crossbar idea would involve sort of building a gantry over the uprights up high. extend the uprights up to the rafters then place I beam across them. The ultimate would be a beam across the whole width of the shop and add lift trollies

 

[52wrench]

That's a great idea. What is the width of your shop? I installed a W8x21 (8" depth, 21 lbs/ft) wide flg. I-beam across a clear 25' span. It was sized for a max of 1/2" deflection with 1 ton hanging from it mid-span. A great addition if you do engine removal work or work on heavy equipment. You would have four uprights supporting it so the beam would be smaller than for a clear span. Just have to make sure the buckling strength of the lift posts and uprights you add to the top of them is sufficient for the load you want to lift. That can all be calculated, no big deal. Or, if you didn't want to go across the full width, just across the top of the lift over to one wall.

 

[lakeroadster]

for lakeroadster:

First, the posts are installed parallel, Second, the vehicle is not attached to the lifting arms. Think.

The columns will be vertical and somewhat parallel, they are fabrications bolted to a floor, there will be movement relative to each other, by design and in reality.

Many lift arms do have tabs on them to prevent the vehicle from sliding off (My Rotary does... and those have saved my bacon a couple times.

Think? I "think" its possible you've never used a lift, that's why you are fretting about it's design... am I right?

 

[52wrench]

Never mind. As I said before, with your philosophy we'd still be using outhouses, driving Model A's, using phone booths, slide rules, etc,etc.

For some unknown reason you can't accept the fact that there are a lot of people who feel more comfortable under a two post with a cross beam than w/o a cross beam even though the OEM design data shows it is unnecessary. People also use jack stands under the vehicle front and rear even if they have the COG located properly between the arms and the vehicle weight is within the limits of the lift. The fact is a cross beam increases the safety factor substantially with respect to anchor pullout due to the moment applied to the base plate by the load trying to tip the posts inward. The degree of increase in SF is dependent on the configuration and material used for the cross beam. For some other unknown reason you also cannot understand that posts CAN be installed parallel. Granted, you have to know how to use a tape measure, read a bubble level and choose the correct combination of shims. You might even have to cut some shims.

I know, "if the company wanted a cross beam they would have designed it originally", "you should have bought a four post", "it is going to put more stress on the carriage and cause binding", etc,etc etc.

 

[lakeroadster]

I "think" its possible you've never used a lift, that's why you are fretting about it's design... am I right?

Never mind. .

You didn't answer the question.

For some unknown reason you can't accept the fact that there are a lot of people who feel more comfortable under a two post with a cross beam than w/o a cross beam.....

I understand, that's why I bought a lift that was designed, built and tested with the cross bar at the top.... and an integral locking mechanism, etc.

I know, "if the company wanted a cross beam they would have designed it originally", "you should have bought a four post", "it is going to put more stress on the carriage and cause binding", etc,etc etc.

Good, very good, grasshopper.

 

[pmiranda]

Just keep in mind that a cross beam that isn't strong enough is not safer than none at all. If you don't trust your anchors, you should fix them.

 

[Strouty]

Do we need to chip in and get you two a room?

The benwil design is much more robust than the one the OP has. As far as attaching a beam across the top, can it be done? Sure, does it need to be done? I think until you put your truck on the lift that remains to be seen. It sounds to me that if you had 12" thick concrete you would still want to put a cross brace because you have never used a floor plate model.

 

[overkill 19]

In my world you would never tie cables to the building from fear of the building / frost moving and actually making your lift worse.
I'd build the cross brace on top. I can't tell from picture but is your top plate on column a cap or does it suspend a pulley? If it were me I'd mock other lift designs and get a column extension bent up and weld a plate on bottom so you can bolt it to that top cap. The cross brace you can make it out smaller material IMO.
I'd also try to run extensions down past top column cap so you in a sense fish plate the extension to existing column.
My 2cents!

 

[52wrench]

Agree, the cross beam and post extensions can be sized to handle a trolley and hoist set up for just the span of the lift or across to the outer walls. That would make a nice set up.

But I'm sure lakeroadster will chime in on why it shouldn't be done, can't be safely designed, blah,blah,blah.

 

[lakeroadster]

blah,blah,blah.

So, could you be so kind as to answer the question?: Do you have any actually experience using an automotive lift, or is all your knowledge "theoretical".

Maybe post up some photo's to back it up?

 

[wssix99]

Manufacturers recommend against these kind of alterations for good reason. I am still not understanding why you fellas are changing lifts that don't have issues, when your changes can result in issues.

This is really it, right? Tens of thousands of these things have been installed per manufacturers instructions without failure. No doubt tolerances have been exceeded many many times.

I'm not sure why the engineers who work for these lift company's are untrustworthy or would be putting the users in a dangerous situation? Is there any evidence to show that these devices are inherently hazardous when used per instructions? If one is afraid of flying in an airplane, afraid of going in a tall building, etc. I could see the fear in getting under a properly installed 2 post lift. But if one isn't concerned with the safety of all our other modern conveniences, I'm not sure where the worry is here.

Adding devices to make things "safer" when one doesn't understand all the various forces involved and at play could easily make tings much more dangerous. The mechanics of these things are really complex. There are many moments, load paths, dynamic loads, and friction is at play. Even though my Mom swears I'm the smartest person in the world... I wouldn't rely on paper equations/calculations for something like this without testing the real-world forces. But - I would trust that a reputable company selling this device to me has done that homework.

If you are really that concerned then make some extensions and spread out the load.

http://www.gregsmithequipment.com/Atlas-Baseplate-Extension-Kit

I think this underscores my hypothesis that the companies who design these lifts and actually test the real world forces on them are more concerned about the forward-to-aft tipping moments vs. anything else. That is the limiting factor and why we are cautioned to balance the load, use props/jacks, when pulling engines/heavy parts from vehicles, or why things like these outriggers are offered. ...Or maybe it points to the Greg Smith lifts being designed a little too close to the edge???

 

[davejo]

Lots of great food for thought.

I worked as a "tire and battery man" at Sears 25 years ago so the lifts I used were single post. I've never been under a 2 post but I trust the design of this floor plate lift.

It's the process of buying it used and installing it myself which has made me think of possible pitfalls and solutions.

I'm learning as I go. For example, the atlas floorplate 12K calls for 6 inch concrete. Further reading shows the baseplate to measure 19 by 24 inches, much smaller than the 24 by 34 baseplate on mine.

Even though my diagram looks childish, I like math and physics and figuring out things with some internet buddies rather than paying somebody to come into my digs and then wondering about the job they did.

 

[brownbagg]

it be easiler just weld the foot print to a four foot by four foot plate about two inches thick with about forty anchors

 

[52wrench]

That's really a nice lift and shop you have. Please don't do the cable tie into the structure thing, do it right with a cross beam that can be used for a hoisting beam also. It will cost more of course but it's the right way to do it. I can help you with the beam and post extension sizing. There's nothing like having a hoist, so much better than the cherry picker floor cranes.

 

[Ironcrow]

...anyone want to check my math?...

I think it would take 3 hours to rig cables....

Math looks OK to me although a 50 inch lever arm seems like a lot, really only about 30 inch in use?

... Remember that the design of a two post lift is to have things as balanced as possible. So if you have a 12,000 pound truck and it weights 3000 pounds on the front axle and 9000 pounds on the rear axle, you are overloading the lift. As a 12k lift, it can only take a maximum of 3000 pounds on each arm.

I would be surprised if a lift were so poorly designed. A real engineer would have the lift strong enough to raise and support its rated capacity on the forward arms only or the rear arms only. If I found company literature that suggested your idea was true, I would question the judgement of the rest of the engineering and either not use this lift or suitably de-rate the whole thing, buying a 12,000 lb lift when I was only lifting 6,000 lb.

....There is absolutely no need to leave any slop when attaching it to the tops of the posts.

Yes. I would not attach the lift to your structure unless the structure was reinforced concrete and I was very thoughtful about the potential loads involved i.e. would you be comfortable bolting the heaviest truck you plan to lift directly to the cable attach point and leaving it hanging there? If not, don't cable.

However, rigidly attaching the columns to each other is a fine upgrade and yes there is no need to allow slop or removable cross brace, just bolt them solidly.