Moment Frame on Asphalt / Wheels?

[KootK]

I've got a client who wants a temporary lifting frame that would bear on asphalt at the column bases.

Do I need to consider the column bases as though they are on rollers? Or am I being excessively paranoid? I'm not sure that I have a friction coefficient for this case that I trust. The bases will be sized precisely to preclude their biting into the asphalt excessively. For all I know, the base plates may land on an old oil stain.

If I go ahead with this scheme, is checking the frame for the buckling mode shown below the only thing about the design that would be different from one where the base connections are laterally restrained?

Generally, is this a crazy thing to do? Would you insist on real foundations of some sort?

 

[canwesteng]

Can you tie the base together with rod or something?

 

[azcats]

I'd be interested in seeing how my structure reacted/deflected with the roller assumption and how much thrust it was actually resisting w/o the roller.

My gut says use the roller or bracket the system w/ and w/o.

If it's stable otherwise and you're comfortable w/ the loading atop the asphalt, I wouldn't insist on traditional foundations. But again depends on the actual loading. Crane guys put large loads on outriggers.

 

[Rabbit12]

What keeps this stable perpendicular to the frame?

 

[jhnblgr]

Is this similar to a four post car lift.

 

[Brad805]

What load are you lifting? McMaster Carr has lots of options you can compare with.

 

[KootK]

Can you tie the base together with rod or something?

I doubt it but I'll ask.

 

[KootK]

What keeps this stable perpendicular to the frame?

Moment frames out of the page. Or braced frames if necessary.

 

[KootK]

Is this similar to a four post car lift.

It would bear some similarity if the car lift posts were not positively attached to something laterally.

 

[KootK]

What load are you lifting?

Centrifuges. Five metric tons.

 

[KootK]

What load are you lifting? McMaster Carr has lots of options you can compare with.

Brilliant. I'll see about just doing that if I can find one to clear 15'.

 

[jhnblgr]

what exactly are they trying to accomplish? Just moving them vertically or horizontally or both? Is this for installation or maintenance? Trying to think of different solutions that might accomplish the same end goal.

 

[KootK]

Is this for installation or maintenance?

Removal and install of the centrifuges.

 

[jhnblgr]

Could they use a jack and slide type system with cribbing if the lift height is minimal?

 

[KootK]

Could they use a jack and slide type system with cribbing if the lift height is minimal?

I don't know, I would have to ask. The client specifically requested the system that I described in the OP so, unless there is some reason that is can't be done, I'm inclined to trust their judgment with regard to what is best for them.

 

[Rabbit12]

Moment frames out of the page. Or braced frames if necessary.

I would analyze these as roller bases. Something like the ones posted above are what I had in my head.

 

[jhnblgr]

Once the unit is jacked up how unstable will it be moving it into position?

 

[KootK]

Once the unit is jacked up how unstable will it be moving it into position?

I'm not sure that I understand the question. The until will be hoisted, then suspended from the hoist, shifted along the hoist beam, and then lowered.

 

[Greenalleycat]

Interesting one
I think I would design it assuming a roller only case, and then the inevitable 'friction of some kind' would be my sleep at night factor

I made a dummy model out of interest - 250PFC (10" channel for your muricans) steel frame, 3m knee and 6m span with a 10kN (1 tonne, 2200lb) at midspan
I had to put a very low stiffness spring on one side to get it to run so all deflection (~15mm, 0.6") went to the left side - in reality, I expect that this would be 50/50 split
This is probably a far larger span etc than you'd use in reality so it doesn't look crazy, though I suppose it depends how much your centrifuge weighs

I think I'd be wanting multiple rows of wheels on each side so that you don't start angling the wheels out and risk breaking them if you have just 1 row

 

[jhnblgr]

I'm not sure that I understand the question. The until will be hoisted, then suspended from the hoist, shifted along the hoist beam, and then lowered.

I was picturing workers trying to push the frame on its wheels but if you are saying only laterally along the beam that should be safe