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I need to construct an outdoor shallow ramp approx 4m long and 1.5m wide for a 1:12 gradient. I'm considering metal sheeting for the walkway rather than decking but I don't know what thickness of aluminium or steel would be adequate or considered typical?

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  • How much weight does the ramp have to support? How will it be distributed? – JACK Jan 21 '20 at 23:01
  • Don’t walk on the steel sheet ramp when it’s wet. It’ll be slippery. – Lee Sam Jan 22 '20 at 0:12
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    One presumes the structural requirements to make the ramp technically useable and the accessibility requirements to make the ramp practically useable are not being considered at the same time for obvious reasons. That's like saying people shouldn't walk around naked outside when it's snowing, after being asked where the local nudist beach is. @LeeSam – Nij Jan 22 '20 at 3:53
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    They make sheet metal with anti slip, and you can treat with anti slip coatings. Wooden decking is also often slippery when wet and liable to rot etc... So let's not get off topic. – Mr. Boy Jan 22 '20 at 9:25
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    You can get diamond plate (or checker plate) which is intended to be walked on. The supplier will have guidelines on construction of a ramp. If the purpose is for wheelchair access, I would ask the wheelchair user if that would be suitable for them. Or does it need to have a high drainage rate, for example for use where waves go over it? – Andrew Morton Jan 22 '20 at 11:42
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I'm not sure "thickness" really matters as much as the overall design of the ramp. U-Haul trucks come with 12' long aluminum ramps that one person can lift and they are made of pretty thin aluminum. They are rated at over 500lbs because of the overall design of the ramp.

Thickness really only matters when talking about one single unsupported span, and that is dependent on overall design. You could have a 24" unsupported span with 1/4" steel or a 6" span with 1/8" aluminum (all made up numbers).

A better approach would be to find an affordable metal that is suitable for the purpose of a walkway, then decide what design would allow you to use that based on its weight and flexibility. Once that is done, you can look at the cost of a more typical surface (wood decking), compare costs, and see if metal really makes sense.

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  • By "overall design" of the U-Haul ramp example, the ramp itself is like an I-beam, where the sides of the ramp provide significant stability to the ramp surface. Of course, this is a generalization, but it goes to show that often the other parts of the ramp are just as important as the surface of the ramp in determining strength. – Edwin Buck Jan 22 '20 at 20:17
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There are online plate deflection calculators. Here is 4 meters x 1.5 meters. 1.5 meters unsupported is a very long distance for a plate. I made some assumptions on the weight and allowable deflection. For 0.1 inch deflection (center displacement), and 500 lbs load (about 2 large people), you need 1/2 steel. This will be prohibitively heavy. JPhi1618's intuition is good, you probably don't want to use a plain plate.

enter image description here

https://www.engineersedge.com/calculators/flat-plate-deflection.htm

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  • Most interesting. I would never have guessed this outcome (I don't 'know' metal like I do wood). Thanks :) – Mr. Boy Jan 22 '20 at 16:58
  • @Mr.Boy - Wood joists for decking are normally spaced 16 inches, a lot less than the span you are attempting. – Mattman944 Jan 22 '20 at 17:00

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