How to find thickness of steel plate 2

[Ron180]

I have a 300 mm diameter hole in the ground surrounded by concrete. This hole will have a steel plate placed on top of it, to allow vehicle transport over it. I need to get a machine of weight 2.5 tonnes across this hole safely without any bending of the steel plate.

How would i calculate the required thickness of the plate?

Thank you
Ron.

 

[Ron180]

The machine is a brokk, so it will be tracks that go over the steel plate. As the brokk may carry stones etc, im assuming a point load distribution for worst case scenairo.
Thank you

 

[CANPRO]

I need to get a machine of weight 2.5 tonnes across this hole safely without any bending of the steel plate

To do this you need to avoid the plate all together. If you load the plate over the hole, it will bend...thats how these things work. Just being picky here I guess.

You have to take a look at Roark's for your answer...this loading case will most definitely be listed in a table there. I don't think you'll have a hard time getting a plate to work. They use steel plats during road work that cover larger hole with larger loads. Not sure how thick they are, but around here they don't seem to be more than 1/2".

 

[Ron]

The hole is relatively small and the load is not excessive...plus the load comes from a tracked vehicle...Not much to worry about here. I would put a 10mm plate over the hole and not worry about it.

If you want to go through an analysis, you can try CANPDRO's suggestion using Roark; however, you will have difficulty determining the actual load on the unsupported part of the plate.

 

[canwesteng]

Plates are cheaper than engineering and a whole lot cheaper than a machine falling in a hole. Make conservatives assumptions about load (point load and one way load distribution if you get away with it) and design for the elastic moment capacity of the plate in bending.

 

[Ron180]

Thank you for all the responses. It has helped me understand alot more than i did previously. I very much appreciate all the comments.
Ron180

 

[racookpe1978]

Your bigger problem than that little 300 mm hole surrounded by concrete will be fixing the plate so it cannot move sideways under friction loads and other unknown forces and vibration. (Will the railroad-like tracks be welded or fixed to the plate?)

The plate MUST overlap the concrete on all sides of the 300 mm hole (which is not really very large) enough so the plate will not damage the concrete lip and the concrete support area for the plate (and tracks). Further, over time, an unprotected exposed edge of concrete will break off and degrade. You need a angle iron 50 mm x 50 or 40 x 40 to wrap around the exposed edge if this is going to be use for a long time. If a temporary fix, you only have to worry about the plate skidding or moving - so add a welded small bracket at each 90 degree point underneath to prevent movement.

 

[msquared48]

That's only a 12" diameter hole! Why all the fuss? 1/2" plate will be far more than adequate.

Mike McCann, PE, SE (WA)

 

[TLHS]

If you're just doing this once for a day or so, just rent a road plate and avoid the trouble. It's overkill for the size of hole you're talking about, it'll cost you maybe $20 a day plus a delivery charge, and may end up being more than the material costs of a custom solution, but that's still cheaper than spending a couple of hours dicking around with engineering and then adding the materials on top.

On another note, I've never seen a brokk, but the pictures look pretty fun.