Steel Uni

Ground anchor, best fixing and max loading?

I need to be able to winch an immobilized car up my drive ( about a 1 in 4 slope) into my garage. I have a pit in the floor and i was thinking of mounting an 8mm thick, 50mm diam steel ring on a plate. the Plate being bolted directly into the end wall of the pit with 4 M12 studs resined into the concrete so that the rope was pulling up and over the end wall and not trying to pull the fixing straight out but loading them at 90°. I can then attach a hand winch to the rope and pull the cars up.

Can anyone offer any practical or theoretical advise, I've done a lot of stress and strain loading and elasticity of materials and UNI but that was a few years ago and i can't remember a thing.

Hum... an 8mm x 50mm ring (5/16" x 2") is a decent size ring.

You do not say if it is welded to the plate, nor give the thickness of the plate, which is critical to determine the stresses.

However, I can make some reasonable assumptions. Assuming your car weights about 2000 lbs, and that it can freely roll on its tires, the wich force should be about 500 lbs.

I would use a safety factor of two to account for friction and impact thus the design force should be about 1000 lbs.

Now, assuming the ring is made of 36,000 psi steel, the allowable stress should be about 27ksi. The area of steel is 0.15 square inches, so the design tension stress is 7 ksi which is about a quarter of your allowable, so I say the ring should be OK.

As for the anchors, they are 1/2" diameter and the shear load on each one is about 250# so the stress is very low at about 1.2ksi, which is more than the typical allowable of about 20 ksi.

If you are using a plate 3/8" thick, you should be ok.

Now, as for the loading, you say you want to load it at a 90 degree angle.

I would say that if you have enough concrete thickess to anchor to the floor, that you are better off loading the thing in tension, i.e. vertically off the floor.

The reason for this is because if you are welding the ring to the plate, the weld works MUCH BETTER in tension than having it loaded at 90 degrees through the ring. An eccentrically loaded weld has much less capacity than a weld loaded axially. I highly reccomend you load it vertically "straight out".

Hope this helps and good luck.

John Steel Singers @ Adelaide Uni O Ball

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