Slab on Grade - Crane Loads

[questioneng]

Does anyone have any resources for checking the capacity of a slab on grade for crane loads? ACI commentaries only discuss vehicle loads, which are lower and long term.

I need to check a one-time 160 kip axle load (putting up tilt-up walls) but am unsure how to check the slab.

Thanks

 

[Urci]

More than likely you will have to design some dunnage for underneath the crane to spread out the load so as to not fail the slab on grade. ie) timber , or timber with steel plate

 

[LowLax]

ACI 360R Design of Slabs-on-Ground has a section on calculating the maximum concentrated load for a slab on grade.

http://www.concrete.org/bookstorenet/ProductDetail.aspx?itemid=36006

 

[hokie66]

I agree with both posts in reply to your query. In addition, for a crane big enough to generate an 80 ton axle load when lifting, I suggest you may need dunnage for driving the crane on the slab, not just for lifting.

 

[TravisWy]

While transporting the crane on the slab; from my experience, the pressure at the surface of the concrete is equal to the tire pressure….that one threw me off a bit when I first heard it but if you think about that it makes sense. The heavier the crane is, the more the tires will bulge and spread out the load. Generally your tires under the counterweights take the most weight, so just treat the carrier frame like a beam and solve the best you can with each axle acting as a pin support.

Solving loading conditions under an outrigger is more complicated. However, a great way we got out of determining this was we placed the entire weight of the crane + weight of object + weight of rigging on one outrigger, and calculated the loading by a 4’ x 8’ oak timber (we usually used 12” thick oak timbers). This is conservative, but if it exceeded the concrete’s strength………a great source of reference is “Cranes and Derricks” by Shapiro. It lays out the required formulas regarding C.G. of the boom, etc., that is needed to accurately solve your problem. But it will take some time and you may not be able to get all the info you are wanting.

One last thing, in the book it talks about the effective length of your oak mats. This basically deducts the amount of area your able to spread out the load….if you have a 4’ x 8’ mat, the effective area could be say 4’ x 6.5’.