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How to lift concrete slab?
5

How to lift concrete slab?

How to lift concrete slab?

(OP)

Hello!

I have to lift 5 ton roof precast concrete slab of elevator shaft to repair.
Isn't there any jackup tool to raise slab only 10" temporarily through 1/2" horizontal joint between this slab and elevator walls?
(Crane cannot access this area.)
This elevator shaft is located at the perimeter of parking structure and about 60ft tall;
two sides are attached to the parking deck.
I am looking for practical solution.

Thanks!



RE: How to lift concrete slab?

If there is not a ready-made appliance for this then I would be thinking about bolting a custom bracket with a threaded rod at three points around the sides of the shaft. There might even be a jack (screw/hydraulic) that is made to be bolted on.

Not especially related, but I recently saw this video on replacing a crankshaft in a large ship. The rigging, techniques, and specially made appliances for the heavy lifting were pretty interesting.

RE: How to lift concrete slab?

I'd leave this post here for a while and then pick what appears to be the best suggestion. We engineers can think about this puzzle and who knows what may come up.

RE: How to lift concrete slab?

can the parking deck handle a telescopic forklift loaded with the roof panel weight? If so local demo to the wall facing the parking deck to allow the forks to enter the shaft wouldn't be awful.

one of these

Open Source Structural Applications: https://github.com/buddyd16/Structural-Engineering

RE: How to lift concrete slab?

I'm not sure if this is being moved horizontally or vertically....but 5 tons is nothing. I've got a 75 lbs, 2.5 ton jack in my garage. You may have to have a custom made cheater bar to shim in that joint and lift it.....but it's certainly doable. I use to work with chemical manufacturers that had a lot of custom made tools for raising equipment and changing out bearing pads or whatever.

A big thing is being sure you don't put the jack through the floor. That's where you come in (as a structural engineer).

RE: How to lift concrete slab?

2
I've used jacking bolts to lift and level precast panels for bridges decks a lot; contractors had no issues and they were relatively inexpensive. Mine are usually cast into the panel ahead of time but I don't see any reason you couldn't modify it to be external to your roof panel; attached with screw or epoxied anchors; and lift the panel the required height. See attached for a concept.

I assume the ultimate goal is to pour a riser to elevate the roof for the hoist beam? If you used screw anchors you could grease with oil or form release agent and back them and the jacking bolts out after the riser concrete has set; grout the holes and be done.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL)
American Concrete Industries https://www.facebook.com/AmericanConcrete/

RE: How to lift concrete slab?

If you use jacking bolts (presumable 4), be sure to calc them out for the critical case where all the load is split between two (if CoG isn't in the middle of the slab one bolt might even see more than half the weight). It's a real slick detail though, probably your best bet.

RE: How to lift concrete slab?

Yeah, that's why I noted 1.5"Ø bolts; the potential for heavy load and the long unbraced length of the bolt requires a large diameter unless you're using something stronger than mild steel. You could probably go smaller with a more refined analysis or specifying stronger bolts.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL)
American Concrete Industries https://www.facebook.com/AmericanConcrete/

RE: How to lift concrete slab?

Slick detail TME. To add on, having those bolts come down to a bearing plate in that gap would not only help out with the bearing situation but probably also make the turn easier on the guy with the wrench.

Did you guys ever do that?

RE: How to lift concrete slab?

There are pneumatic bladder lifting devices out there - you could slip in a bladder on each side/joint and inflate - then place temporary supports to allow access.

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RE: How to lift concrete slab?

For raising via the four bolts, Mighty Engineer's, what is there to prevent all four bolts drifting sideways or in a circle? Then the whole system is stick part way done and useless with bent raising bolts. There must be some form of bracing so that there is no drift. The inflatable jacks less chance to drift, assuming tough balloons, and can be pushed back in place..

RE: How to lift concrete slab?

Quote (WARose)

Did you guys ever do that?

We're usually jacking precast bridge panels on steel girders but I imagine a little bit of grease squirted in the hole would solve the problem of it binding up and/or grinding it's way into the concrete below. You're right, once it's up enough it would be good to back off one at a time and put a bearing plate in there.

Quote (JAE)

pneumatic bladder lifting devices

Good thought! They can lift quite a lot and are easy and inexpensive. Might require a minor demo of the concrete joint to get it in there and started but if you're casting concrete to raise the roof panel anyway then it's easily patched at the same time.

Quote (og)

There must be some form of bracing so that there is no drift.

Oversized bolts designed as short columns and the coupling nut is there to provide some fixity. Granted; my bolt jacking detail is normally embedded inside a precast panel so that welds on the coupling nut combined with the plate might be too flexible and result in exactly what you described. That said; I've used that jacking bolt detail on 4 bridges now and not once did a bolt get bent or report as being stubborn; that's roughly 1,000 bolts having been used to jack panels panels a lot heavier than 10 tons. I'm fairly confident the method is sound.

Pictures of jacking bolts in action:

Construction loads on jacking bolts

Wide angle of bridge panels

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL)
American Concrete Industries https://www.facebook.com/AmericanConcrete/

RE: How to lift concrete slab?

Nice to hear. However, at this site there are only a few bolts and conditions are not ideal as to access,etc. Not much redundancy. I'd take no chances and maybe double the number of bolts. Maybe a plate at each bolt tip with a circular weld bead for better positioning in tight area.

Edit. Supppose the job runs into trouble due to lack of lift height or other reason to go higher. Run up a few bolts at a time and set blocking underneath. Do in sequence to get what ever lift you want.

RE: How to lift concrete slab?

Good suggestions so far. One more to add to the mix - anchor a lift across the top of the slab and install jacking brackets on the sides of the shaft...place bottle jack between the beams and brackets.

If the roof panel is 5 ton, I'd account for at least a 7-8 ton force required to lift it up. No real science behind that, I just know when you're lifting old stuff, you never know what is in there to bind things up, and if practical, its a good idea to add a healthy allowance for that.

RE: How to lift concrete slab?

Hire riggers and let them figure it out.

RE: How to lift concrete slab?

Demo the slab and put back a removable roof system for the next time this happens. Small area.....or maybe if you raise the roof height a bit, you won't need to remove next time, since you only need to raise 10 inches.

RE: How to lift concrete slab?

I vote for jacks or air bags and vertical timbers

RE: How to lift concrete slab?

Do like Mythbusters and get a bunch of vacuum cleaners and some hoses and tupperwear bowls and suck it up.

RE: How to lift concrete slab?

Perhaps notch out the wall at several locations around the perimeter and use hydraulic jacks. Add some vertical guide bars to make sure the panel cannot go sideways. It can go up a few inches, add some cribbing, and then shim the jacks to lift it some more.

I am reminded of this guy: https://youtu.be/E5pZ7uR6v8c?t=166

RE: How to lift concrete slab?

I like that video 3DDave. I worked on project remodeling an old farmhouse, where I was just the teenager 'grunt' laborer and the structural engineer they had on site leveled up the entire house with wedges of 2x4s. He cut some 200 wedges and pounded them in with a sledge hammer various amounts, raising it as much as 3" to compensate for the foundation settlement. It could work here, but there's surely less time-consuming ways, such as the approach you suggest in your post.

RE: How to lift concrete slab?

I'd go with TME's original suggestion, but do what sreid says: tell the riggers this is how I'd do it but you guys go ahead and get me the lift I need. Really, with a decent contractor on this one the engineer is just there to calm the other parties down.

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