6 ton crane on 6" thick concrete slab safe

[ben3929]

I recently assigned to a project to design a steel structure for a 6 ton overhead crane and i am very uncomfortable that my lead design engineer suggested to install the crane on a 6" thick concrete slab. The ground floor slab (f'c=3700 psi) is rated for 600 psf and I recommended to install a pile foundation. my question is, would it be safe to install a 6 ton crane on 6 inch thick slab.

 

[MikeHalloran]

My question is how do you throw a flag on the play, without getting yourself fired, like I always do?

I have no answer for my question, but I think you know the answer for your question.


Mike Halloran
Pembroke Pines, FL, USA

 

[JAE]

ACI 318 requires a minimum of 8" thickness for footings. Your 6" slab obviously doesn't qualify.

I would also think the punching shear would fail as well...unless you have a 4 ft. square base plate or something.

 

[rowingengineer]

I'm confused.

I am assuming this is a portal framed building with steel columns onto a slab.

would you require piles, what about large concrete footings, what is your hd like.

or is this a jib crane.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[ToadJones]

Well, not to be "that guy" but "6 Ton Crane" really means absolutely nothing to me.

Is it a 10ft span crane?
Is it a 100 ft span crane?
Double girder?
Kit type crane?
A six ton crane could have wheel loads of 25 kips or 5 kips and foundation reactions that are somewhat proportional.

 

[dik]

JAE and Toad has pretty much summed it up... although a 6" slab on OK material if properly reinforced (try squeezing 2 layers of rebar into it) can support your 15 to 20K reaction (for a small crane) any sort of frequent use will likely break it... best to use 8" min...

Dik

 

[FLCraneBuilder]

Mr Toad is right, simply stating crane capacity as 6 tons does not explain much in terms of the actual load on the concrete. could be 7000# col load - could be 70,000# col load.
I will note that we have successfully put light capacity crane systems on existing 6" concrete slabs. Large column base plates help. Insureing adequate subgrade modulous contributes as well. I assume you are planning on the crane columns being braced to to an existing building structure. A 6" Slab cannot take much in the way of moment loads

 

[zcp]

Run the numbers and come to a conclusion on your own. Then take the lead to lunch and discuss.

ZCP

http://www.phoenix-engineer.com

 

[racookpe1978]

Concur with the above.

First, figure out what the TOTAL crane weight is (plus overload and margins are), NOT what load the crane can lift or what its capacity is at some lift radius.

A six-ton crane could be a truck-portable four wheel road rig on four 2 ft x 2ft steel pads while lifting a 6 ton load (12,000 lbs alone) at 100 feet radius - total weight on the concrete might be upwards of 50,000 - 80,000 lbs. (And what happens when that crane isn't available, and the contractor brings in the "next biggest" crane that weighs 100,000 lbs?)

Or it could be a rail-mounted overhead jib boom whose load is carried to the structural steel already in position.