Loading a BendPak Asymmetric Lift

[mslisaj]

Hi Chris,
Interesting comments here but I believe you made a mistake. I have a BendPak Asymmetric lift and that is the lift that BendPak states can lift in the symmetric and asymmetric configuration with their "tru-metric" arms. But then again it seems they ship all their lifts with these arms as I just saw a symmetric 10K lift with the exact same arms that I have. I have looked through the BendPak site again and the true symmetric lift talks about "lifting the heaviest loads". But all that aside Daedalus makes a great point about the twisting moment at the attachment point at the column. This can be easily overlooked. Again BendPak in this thread through Jeff states that the main point to remember is don't overload each individual arm over the 2500# rating for a 10,000# lift. In fact this is why I started this discussion in the first place. It seemed odd to me that you could put 2500# on the rear arms and 1000# on the front and that's okay. But apparently as long as you don't go over the 2500# per arm on the rear and you have a good floor then the anchors will take this load. Suffice it to say that I only load in an asymmetric fashion very light or small cars. There I may only put 1000#s on each rear arm and 500#s on each front arm and the lift has enough capacity to handle this load. But if I put anything up on the lift with any size or weight I center the load between the columns the best I can. No matter how you're looking at it you're still doing a huge balancing act with this style twin post lift..............
Lisa

 

[saabman]

Hi Lisa,

I see symmetric and asymmetric loading terms used a lot without clear definition. Based on what I read in threads on this forum, some implicity define equal arm length as symmetric loading. We should better use centered mass and off center mass. Generally speaking you cant tell if it is symmetric or asymmetric based on arm length alone. But you can get twist from the disparit length arms (levers) even with centered mass. One reason I went with the normal width (aside from conserving shop space) is my cars tend to be narrow. Having wide column spacing means the arms extend further increasing the corner weights twisting action on the column. I have the corner weights on my race cars and that will allow me to accurately figure the center of mass.

I should have better clarified my comments in the context of lifting sports cars (2000 to 4000 lbs). Curiously, one of my cars has a 60/40 weight distribution and an 84 inch wheelbase, the center of mass is quite close to the front jack point. I expect the front arm on the lift to be close to 90 degrees (with center of mass dead center on the column). In fact many of my cars are FWD, which puts the center of mass forward making it unneccesary to asymmetrically load.

I was out in the garage this morning scoping where to put the columns. The odd ball vehicle is my K1500 Ext Cab truck. I suspect even symmetrically loading it, much of the truck will be in back of the column. So my overall bias is going to be to leave more room behind the columns than in front.

Chris

 

[mslisaj]

Hi Chris............

Great response on the symmetric and asymmetric. The different length arms are referred as the simple definition. Actually the 30 degree turn of the columns is said to keep the load centered into the columns. At any rate the "center of mass" loading is the key phrase to use. Center the load between the columns especially when the load goes up in weight.

On positioning the columns can be tricky. BendPak really doesn't speak to the positioning very much but I downloaded manuals from different lift manufactures and there will give specific distances for the setback of the posts. I used 30 gallon drums to simulate the column position and then pulled the biggest vehicle into position. "They" say you should leave 3' in front of the vehicle if you have the room.................. Just some idea's I used.

Thanks to the contribution on my lift loading forum. You have added to the discussion.........

Lisa

 

[saabman]

Lisa,

I tried to use the simple lanquage on my first post, and in hind sight I should have said unequal length arm loading will be my norm (and this is what BendPak sanctions on a symetric lift). Good idea with the drums, I have some garage door tracking that dictates the rough limits on how close to the door I can be. Even the XPR-9F is close to 11 feet tall.

I almost went with a Rotary asymmetric 10k lift, especially when I found out it could be modified to fit in no more than 11'ft 4 " but the price was just to much to swallow for a home lift. But anyone with a height constraint should look at the Rotary lift. With the mod I refer to (factory approved BTW) it is the shortest of all the commerical grade 10k top cap lifts.

Did you use conduit or SO cable to run power to the lift??

Chris

 

[mslisaj]

Hi Chris...........

You're correct on the unequal arm length loading. This was a hard concept for me to get my arms around. When if finally sunk in about the 2500# arm load limit and I had this discussion with BendPak did I then bring up that the anchors must be doing a hell of a job........... With that said, I think you made the best choice with the BendPak. I know that comment will upset the Rotary folks and that is not my intention but you need to check out the comparison that BendPak did with the Rotary part for part and there is a big difference. Check it out and you decide. I didn't have a height constraint in my shop but you make a good point there too...........

Again I appreciate your input Chris............

Lisa

 

[saabman]

Lisa, et al

I think we have the force discussion all wrong. After talking to a Mech Eng buddy he has turned my thinking around. Basically when a car is raised on the lift the opposing arms form a rigid horizontal element (with the car in the middle). As long as everything remains rigidly aligned the force transmitted to the columns is 100% (or nearly so) down. The primary force on the floor anchors is SHEAR (the bottom of the column wants to kick out or rotate) not TENSION. Which is good news as concrete floors are real good with sheer force. Along these lines it is false thinking that a bottom plate lift is inferior to top bar at keeping the columns from toppling inward. In fact if the top bar sees compression force it would likely buckle IMHO. The actual length of the arms also has no bearing on the force tranmitted down, that is simply the weight of the car. Nor does it matter if the lift is center of mass balanced or not. I draw an analogy to the truss roof on most houses (or garages). The roof puts a dowward force on the support walls, it does not splay the walls outward. It does strike me that when do a non center of mass balance lift, the floor anchors (in tension) do work to keep the lift from falling fore and aft.

Chris

 

[Ironcrow]

saabman,

Your thinking is all wrong. Unfortunately, the thread will now be derailed while we get you educated. I don't have time to deal with this now. I'll check back later.

 

[saabman]

Ironclaw,

I am a computer engineer by education and training, so these element analysis problems are not my strong suite. I would very much welcome a correction to my thinking. (Lisa, I dont mean to thread jack but I think a proper understanding of the theory helps in setting up and using the lift). My lift has an ETA of Oct 14, so this thread is right on point for me too.

Chris

 

[Ironcrow]

Basically when a car is raised on the lift the opposing arms form a rigid horizontal element (with the car in the middle). As long as everything remains rigidly aligned the force transmitted to the columns is 100% (or nearly so) down.

This is true only if one welded the car frame to the lift arms. For better analysis, the interface between the lift pads and car should be considered to hinge and slide. Hinge with zero friction. Sliding friction is not zero, but an engineer would assume it so.

Along these lines it is false thinking that a bottom plate lift is inferior to top bar at keeping the columns from toppling inward. In fact if the top bar sees compression force it would likely buckle IMHO.

Some cross braces are thinner bolted assemblies that route power or safety cables over the car. They may not be very strong. Other lifts have side columns that extend to the full height of the lift and the cross piece is more substantial, clearly enough to support the compressive load without buckling.

I draw an analogy to the truss roof on most houses (or garages). The roof puts a dowward force on the support walls, it does not splay the walls outward.

Again, the truss is a rigid assembly. A car on a lift is not.

It does strike me that when do a non center of mass balance lift, the floor anchors (in tension) do work to keep the lift from falling fore and aft.

Yes, the so called 'asymmetric' lift will load the front mounting plate bolts in tension. The primary force of concern for all of the floor bolts in a lift column is tension. The bolts are pulled out with any toppling moment applied to the column. There is some small shear of course, and the compressive force on the concrete pad to hold up the weight of the car and lift.

 

[saabman]

Thank you for the clarification. Further analysis is way out of my depth.

BTW, my Mech Eng friend says that it is still pretty much a "static" analysis. That the pads dont move on the car therefor they are as good as welded on, the arms and the column are as good as static (flex very little) . He does admit that it becomes a dynamic analysis as spot loads are placed on the car (as might occur when you work on the car).

Also wedge anchors put compression load on the concrete. The reason for 150 ft lbs of torque is to preload them with more tensile load than they will see in operation.

Chris

 

[Ironcrow]

I will assume your engineer friend is good at whatever it is he does. I hope it is not lift design.

 

[mslisaj]

Well Gentlemen, you have added some great input here and the discussion continues. Don't worry Saabman about hijacking the thread, all discussion is welcome and I learn a little from everyone. I did start another thread a week or so ago asking if anyone had ever seen or seen pictures of a lift failure and the best response was from a gentleman that referred to the TV show Wrecked. There they had a Challenger lift that you could only assume was loaded way aft with a big Dodge van. The front anchors pulled straight up out of the concrete proving the point of Ironcrow. With all the input here this sort of proves the common sense idea of what would happen with a heavily loaded asymmetric lift is shown graphically. The reason I started this thread and asked the question was how does the lift physically do what it does. The bottom line is it has design limits of 2500# per arm for my BendPak lift and if you don't over do that you can do the asymmetric thing. But as the load of the vehicle goes up in weight the closer to center CG I try to load the car, even if I have to use a ladder to crawl out the window to get out without opening the doors. In reality this is common sense and those of us that don't want to loose a car will think like I do and be better safe then sorry............

Lisa

 

[mslisaj]

Hi Chris,

Great response. I have a 66 Chrysler New Yorker that is about the heaviest thing that I have to put on my lift. I have the factory manual that gives me a measurement within 4" of where the center of the car is. I can balance this car with in this limit and that carefully watch the posts sighted to a solid object on the wall. I can see the post initially deflect forward about a 1/4" as the lift assumes all the weight of the car and then it settles right back to center. I move the car back 4" and I can see the same thing in reverse. If I'm really careful I can actually center this car to such a degree that the post doesn't deflect at all. This measurement is within the 4" factory leeway. But now I know I can very carefully load this car to exact center of lift. I caught this deflection of the post by accident as you can't feel or really see the post deflect. In a previous post to this thread a gentleman made the comment that the most stress is placed on the lift right when the car comes off the floor and I have to concur that this is what I see. It's all design but I just wish I could really understand how it works. I guess I need an engineering degree but I am very comfortable working under this lift with anything I put on it as I am very careful and check everything.

Have a fine day..........

Lisa

 

[Ironcrow]

A note to Saabman and other readers:

... Mech Eng friend says that it is still pretty much a "static" analysis. That the pads dont move on the car therefor they are as good as welded on, the arms and the column are as good as static (flex very little)

Your friend's description of the loading condition is not demonstrated in either the pictured failure nor the Greg Smith video collapse:

http://www.garagejournal.com/forum/showthread.php?t=48867

 

[SeanM]

Is this horse dead or can I still poke it? As an ME I am now determined to do some calculations once I get my lift installed next week (so I can get real dimensions as the ones provided are pretty poor detail).

There is no doubt that the in an asymmetrical lift that the base plate bolts are in tensions. I would just like to get a better idea of how much. According to MaxJax they are rating the tension at a 4x safety factor. Which to me in a pretty much static application is still unacceptable.

 

[mslisaj]

Welcome.............. As far as I'm concerned, and I started the thread it's not dead. I'm still looking to run into a ME and scratch his brain on this. All I know is I load the lift as centered as I can when the load approaches anything over 3,000 pounds. I know this is a 10K lift but after all I'm the one standing under it. There was a lot of interesting information and discussion on this when this thread was hot and active but new opinion's are always welcome. It still boils down the concrete strength and anchors. But a true analysis would be cool to see................

Please comment back at your convenience...............

Thanks,

Lisa

 

[Oldtymeflyr]

If lifting a 7.3 Ford Diesel, just sweat first and be extremely careful, they are the beasts that weigh in at 8,000#+.

 

[3x9RT/SE]

Hi Lisa,

seeing you are/were on the subject of anchor/concrete strength,I will add alittle then.I bought my Bendpak XPR-9FS a few months ago(love it BTW),as the part # shows,it is a baseplate with no overhead connection.I myself,while waiting for the lift,did alot of research/homework on the anchoring to the floor as you can be pretty confident the lift,as long as you do not exceed the rating,pretty much is not going to fail,bottom line!!!
So with that said,it is pretty obvious that the stress (tensil)is on the outer 4 bolts of your baseplate.You can see this as when you raise something with some weight to it,the columns go toward eachother(overexagerating)abit,so those outer 8 bolts are holding something.Picture it,if you did'nt bolt the lift down at all,and tried to raise a car,what DO you think would happen?Both columns would basically come inward right toward the car.
Noone has even mentioned that if you read the specs on a certain manufacturers anchor bolts,they have different ratings when the depth of which they were installed at changes,I.E,the deeper they are set in,the rating goes up on tensil load that the same diameter (3/4'' inthis case) will hold.Don't quote me,but something like 3 1/2'' down was around 10,000lbs,and 5 1/2'' down it jumped to almost 15,000lbs.Same 3/4'' bolt,just longer and set down deeper in the concrete.
In my situation,knowing I was going to put in a two post lift,I poured the floor 6-7'' thick.So when I got my lift,I went with 7'' long 3/4'' anchors,so mine are basically down in there around the 5 1/2'' range.
Also,there has been many a topic about setting them.1st, NEVER impact them in ,period!!!! The usual is once you bang them in and they seat against the lift,3-5 full nut turns and they are set.Others say 80 ft lbs torque them,some even said 150lbs!!!! That is just way to much as some people said they were literally pulling them out of the floor trying to achieve that setpoint.
When I first set mine,I used a long box/open end wrench and got the 5 turns out of them.Used the lift a few times and decided to recheck all of them,and some slightly were able to turn them somemore already.Again doing more research,was educated as these style bolts,after being set,was told the bolt will "relax".
If you have an extra bolt kicking around,like I do,you can easily see that 3-5 turns is only about 1/2-5/8ths''.Take a close look and measurement of those wedge bolts,that "cone that wedges itself up on the ramp,persay,would need about 1 -3/4'' to pass completely over it and pull through.If this were the case,and you COULD tighten them to do so,you would see 2'' + of your threads visible and should know something went terribly wrong!!!!
Now lastly,as said,these are wedge bolts,as the weight of the load is going up on the lift,if it were enough to apply extreme force to try and pull the bolts out,again,it would be just like simulating a tightening of the bolts in the first place and would only wedge themselves harder and inessence,being acted upon like they were being tightened with a wrench!!!
It,to me would have to be a catastrophic failure,which would'nt be good.And as you yourself said,usually the cars are falling off by user error of the loading of the vehicle.
To also show you my relm of thinking,I have been doing HVAC/sheetmetal/ductwork for 23 years now,90 % of everything I install is usually above the ceiling and hung from the deck,either off steel beams OR,like our lifts in question,drilled into concrete slabs above and using expansion anchors!!! We use the same anchors ,but 1/2'' to hang airhandlers,units,VAV's,huge heavy ductork,etc.I drill,set the anchor in,tighten it and leave the nut and washer there,rod coupling with threaded rod down to angle iron or uni-strut.Think about that,that anchor will ALWAYS have load on it till the piece of equipment is removed!!!!!NTM,have fans in them creating alittle vibration to boot!!!!
Our lifts get lunch breaks alot!!!!LOL I'm sure if you go back and check your bolts,you'd be suprised at were they are right now,while you are using the lift.
Think of how many shops out there have lifts going up and down every day,while never performing maintenence,and fastener checking!!!!!

Food for thought!!

 

[mslisaj]

Great response 3x9RT/SE. You certainly make a lot sense here and we can rest assured the bolts will stay put. My lift has the top plate and as I have mentioned earlier in this thread as the lift assumes the load the towers will deflect back ever so slightly and then straighten right back. I have moved the car back and forth to get this not to happen and I can literally balance the car where there is no movement.

I will have to agree with your first point though which I think is by far most important. I have a 10k lift and Bendpak has told me that each pads maximum rating is 2500 pounds. If you don't overload any one pad or pads you are working well within the design of the columns and the concrete.

Another thing that you mentioned was the listed torque. 80 or 150 ft. pounds. You can feel with a breaker bar when those bolts are tight. I have attempted to pull that 150 and while that is a hard number to hit it just feels like over torque. The nut is tight and just feels solid.

Thank so much for your thoughts here. It's truly an education..........

Lisa

 

[Air_Cooled_Nut]

...
4) To achieve the calculated safety factor of 400% the rated pull-out of the anchors MUST be achieved at 12,580 pounds. My lift has set-in-concrete anchor sockets. If I was forced to mount another lift with drill and set anchors, I would consider epoxy as well as expanding bolts. I would also test each and every anchor at, say, 10,000 pounds. Well equipped contractors who do this kind of work have calibrated hydraulic jacks specifically for verifying anchor pull-out for governmental inspectors. Even if not required by any law, I would obtain the services of such a contractor.

Would performing this test destroy or weaken the anchor in the process?

Anyway, this discussion has me worried about the shop I acquired. If the house is any indication of the shop :tard:then I would be best off in cutting out the floor where I want my [eventual] lift and pouring the appropriate concrete with depth. ****.

 

[Dragster Racer]

Where do you get charts showing the cg for different vehicles?

 

[mslisaj]

Happy New Year Gentlemen!

On the question if the "pull test" would destroy the anchor I would say that if it came out or broke it wasn't installed correctly or was the wrong bolt for the application. Not a bad time to figure that out before you get a big car or truck on the lift and let the anchors get tested with that method and more to loose.

On the CG charts well interesting enough I have some old service station lube charts and they have the CG and lift points for many cars. Getting into later stuff my Motor's and Mitchell Manuals give the information. But again I'm working with older vehicles. With the '66 New Yorker that I will put on the lift I have the CG numbers for that and they are dead on to what I see happening with the columns when I lift it up. So this information is out there...........

Lisa

 

[mmb617]

On the CG charts well interesting enough I have some old service station lube charts and they have the CG and lift points for many cars. Getting into later stuff my Motor's and Mitchell Manuals give the information. But again I'm working with older vehicles. With the '66 New Yorker that I will put on the lift I have the CG numbers for that and they are dead on to what I see happening with the columns when I lift it up. So this information is out there...........

Lisa

My Bendpak came with this book:

Of course it only covers the last 20 years but a lot of cars older than that were full frame where the lift points are easy to find. I find it to be quite helpful.

I'm sure this book is available through ALI.

 

[Ironcrow]

Where do you get charts showing the cg for different vehicles?

You drive to a commercial scale like at a landfill, landscaping material, feed store or something. Drive the front wheels onto the scale, record the weight, pull forward until just the rear wheels are on the scale, write down that weight. The ratio of weights is proportional to the location of the cg. Example: if the front is 2000 lbs and rear is 1000 lbs (2000/1000 = 2) and wheelbase is 120 inches - the cg is 80 inches from the rear axle and 40 inches from the front axle (80/40 = 2).

The sum of the weights, of course, is the total weight of your vehicle. Compare that to the rating on your lift.

 

[pattenp]

Here's the math for the above example..

1000____________________________2000
[0-----------------------------------120]

(1000 * 0) + (2000 * 120) = 240000
240000 / 3000 = 80
CG is 80” from 0 (datum).

 

[Dragster Racer]

Here's the math for the above example..

1000____________________________2000
[0-----------------------------------120]

(1000 * 0) + (2000 * 120) = 240000
240000 / 3000 = 80
CG is 80” from 0 (datum).

Makes sense. I was just hoping there was an easy pdf out there showing most vehicles. I will visit a local scale.

 

[pattenp]

I have the lifting point guide for 1984 -2003. If vehicles you are interested in fall in those years tell me what they are and I'll copy those pages for you.

Here's a page example: View attachment Lift.pdf

 

[Air_Cooled_Nut]

You drive to a commercial scale like at a landfill, landscaping material, feed store or something...

For those in the Pacific northwest you can use a logging scale. There are many along interstate 5 and on the highways (these are normally empty).

 

[juiced10]

I bought that lift guide when I bought my lift from this place http://www.autolift.org/store.htm#ALILPGUIDE Waste of money imho but is only $10. Once you get used to using the lift it is easy to envision the CG.

 

[aarcuda]

Awesome discussion and one that I learned quite a lot! Thanks everyone!