Deflect Steel Plates for Crane Outriggers

[jw2007]

I am placing a small crane on a concrete deck. The deck live load is 760psf. The crane is 17,260lbs. Each outrigger base plate contacting the deck has a surface area of .75 sq. ft. This gives a load of about 5753lb on each base plate. I am going to use steel plate (A36 plate) under the outrigger base to spread out the load. To determine how thick the plate needs to be I believe I need to determine the deflection of the plate to ensure the ends don't turn up and concentrate the load on an area smaller than the whole plate. This plate sits in a flat concrete deck and I am not sure how to determine the deflection. I am familiar with beam loading to some extent and need to know if I would figure this like a beam. Thanks.

 

[Baluncore]

The crane is 17,260lbs. Each outrigger base plate contacting the deck has a surface area of .75 sq. ft.

When lifting a load, the mass of a crane must include the load being lifted and the geometry of the lift. It is most unlikely that the load will be shared equally by the outriggers. It is more probable that a line through only two outriggers will act as a fulcrum bearing twice the crane weight. Even that load can be exceeded in some situations.

The outrigger should seat on a stable flexible stack of interlocked heavy timbers that are arranged to deflect, and so to spread the load evenly over a wider area. You must consult a qualified crane operator.

Flat steel plate is quite unacceptable as it simply does not spread a point load on concrete. It also has a poor friction coefficient so the outrigger foot can very easily slide off the plate.

Because 760 psf is much lower than the normal road wheel loading of 10,000 psf, you may need to lower the crane tyre pressure or prepare a timber mat before traveling onto the concrete deck.

Take plenty of photographs before the lift to provide evidence for the insurance claim and the coroner's office.

 

[jrmichler]

Concrete floor / deck load ratings are for distributed loads. If you have a concentrated load, there are separate calculations for the punch through load and for moment loads. This is discussed in books about concrete design.