fork lift load on 3" elevated slab 3

[COEngineeer]

I have a 9"x20"+3" concrete joists. They are going to install a 2400 lbs generator that requires the use of a fork lift. The fork lift will drive through this 3" slab loaded with the generator weight. Can someone point me to the right direction on the analysis on the slab? Ive analyzed the beam and I am comfortable it will support the load but I am worried about the front wheel load resting on the 3" slab. I havent done any AASHTO design so I am not sure what I need to do with this kind of load. Do I need to magnify it since it is a moving load? HOw about the area in contact to concrete? Anyway, any tips would be appreciated.

Never, but never question engineer's judgement

 

[jike]

3" is not much of a slab plus you may only have wire reinforcement in it which could be located anywhere. I would not let a fork truck on that floor. Perhaps a cart or a skid might be more appropriate.

With a cart, all 4 wheels might have about the same load 2400# / 4 but a fork truck would be carrying the total load on only the front wheels plus the weight of the truck. Check to make sure the wheels do not punch thru the slab.

 

[PMR06]

What spacing are the joists? If the slab does not work, or if you are uncomfortable with them driving on it, perhaps you require crane mats be placed over the slab which are capable of spanning between the joists.

 

[hokie66]

Agree with PMR06. You will need to spread the load in some manner rather than placing wheel loading over the 3" slab. I wouldn't do a lot of analysis, just stay off the slab with the wheels.

 

[COEngineeer]

The joists are 2'-5" apart. I will research about crane mats. I am not sure how to specify one.

Never, but never question engineer's judgement

 

[DTGT2002]

Another option would be to support the slab from below with sufficient shoring to support the slab.

That said, coming up with an adequate dunnage system will likely be easier.

A crane mat is typically a series of heavy timber boards, often oak, sometimes pine, secured together such that the "mat" can be placed on the path a crane or other heavy equipment must travel and not overload the soil. Its application here would assume that the wood members have sufficient capacity to carry the load in place of the slab and are sufficently stiff to prevent the members from simply transferring the applied load in bearing. However, with a thick enough mat and your tightly spaced joists, all loads might be sufficent to assume bearing to the support anyway.

Are there limitations of the height in this area? Would building up a mat of wood or steel members be feasible?

To get aroud the members bearing on the slab you are trying to protect, I have used wood blocking aligned with beam members such that the dunnage members, which have the strength but lack the stiffness to load prior applying load on the slab, will span over the blocking and have a space to deflect.

Do you have a spec sheet for the exact fork lift to be used? This is not the first time this scenario has occurred and the contractor and forktruck manufacturer can provide a substantial amount of data about the lift.

Good luck and post back.

Daniel Toon

 

[COEngineeer]

Putting wood member at each beam is a good idea. How do they line it up though? I dont think you can tell from the top where the beams are accurately and I dont feel like telling them to use a special instrument to find out where they are. Is there an easy way to line it up?

Never, but never question engineer's judgement

 

[DTGT2002]

If it is open below, as built the locations.

No matter what solution is chosen, work will need to be done and money spent. Is a system of dunnage so stiff that the slab will not be engaged cheaper than the hours needed to locate and properly layout the joist pattern at the top of slab? Probably not.

Have you been involved with the contractor or personnel responsible for performing the work? Do they have any ideas?

Seeing as my specialty is shoring, I'd be inclined to support the slab at a tight spacing and use plywood or sheet steel to locally protect the slab. But without knowing the particulars of the equipment and building, it is impossible to determine the best solution.

Communication between yourself and those implementing the solution will be key to the success of your efforts.

Best of luck!

Daniel

 

[COEngineeer]

You are right DTGT, I rather put a blocking between joists. Thank you for your help. I found a company that will rent out crane mats for $1.50 /sq ft. It is 12" thick, 4' wide and 24' long. I am pretty sure this thing can span 2'-5 with the load I have.

Never, but never question engineer's judgement

 

[civilperson]

A steel plate rental will be easier and probably less cost.

 

[COEngineeer]

civ.. do you think I should just lay it flat on the slab? Do you think the plate (not sure how thick it is) will be stiff enough to distribute the load to the beam? Or do you think you will get a focused stress on the slab?

Never, but never question engineer's judgement

 

[PMR06]

Cost & ease of installation aside, 12" thick timber mats would be around 100x stiffer than 1" steel plate.

 

[JLNJ]

Be careful!

A two ton forktruck has a loaded front axle load in excess of 10,000 pounds (5000# per wheel).

 

[msucog]

i'd be scared to put a loaded forklift on 3" of concrete on mediocre subgrade...much less in the air. i suggest using caution with how you proceed. the steel plate on top of dunnage or a thick timber mats seems like a good approach to me...me being a former contractor and now a geotech and materials kind of engineer (not structural).