advice on custom steel platform needed

[Maltes]

I understand this is the last place I should be asking this but what the heck, some of you work in clubs or discos and might have experience and advice on this.
Basically we need to prepare a steel platform where 1-2 people will be standing on and dancing. Size is a 1 by 2 meter rectangle. The edges can be reinforced by steel bars, but only the edges. It's hard for me to explain why I need to use steel and why only the edges can be reinforced right now but it has to do with specially positioning bounce mirrors to get a very specific effect with a laser projector. I will get some pictures/videos when we get it done.

My question is this: How thick of a steel sheet should I go for for a 2x1 meter platform which after having its sides reinforced with steel bars will be able to support two people (200 kg to be on the safe side) without flexing too much and causing the dancers to trip and fall from the curvature?

[lasergrazy]

Maltes,

Look in some steel diament plate, by weight 1/8 " should hold it but will flex , use 1/4 " to avoid flexing.
if you make a frame from square tubing around it.
Will be some what heavy......
Albert

[Maltes]

Thanks. Yes, it's going to be heavy...
I re-checked our CAD drawings and we can actually have a square tubing going from the middle as well without interfering with the beam paths. That will make two 1 square meter areas, not one 2x1.

[planters]

You say steel, but do you mean that metal ie aluminum would also work? I ask because you can get light and very strong aluminum scaffolding, used in construction and by painters. This is a hollow rectangular tube roughly 2" x 19" and up to 120" long. It has a non-skid surface and of course you could cut it to any length you need.

http://www.scaffoldmart.com/scaffold...FYcmhgod5sEJeA

[Maltes]

That won't do the job for this project but I'll keep it bookmarked for future use, thanks!

[kitatit]

Hi Maltes.

What construction methods do you have access too?

I'd use 19mm form ply for the platform and weld up a frame to support it. Use 20mm x 50mm x 3mm wall thickness rectangular hollow section steel for the support. You should be able to have no support legs in the middle with that. The ply can be screwed to the steel or weld tabs to the corners so the ply just sits there but won't slide around.

If you want only steel, 3mm, 1/8" will be plenty, as long as it's supported by a frame like mentioned above. As Albert mentioned. 1/4" will be heavy, like 102kg.

Kit

[Maltes]

Thanks. The main reason to go with steel was to be on the safe side for the dancers. Since I haven't build something from (ply)wood or other materials which were meant to support weight I don't have experience on this. Is there some chart or rule of thumb to use for finding out how much weight a certain size and thickness plywood sheet can support or is that number coming from your experience?
I have access to a drill press, wood and metal CNC and welding.

[planters]

The problem you will probably find is that the strength will be less of an issue than the stiffness. The plywood will flex disconcertingly long before it breaks. If you are looking for a rule of thumb, consider the joist spacing in most modern construction. With 3/4" fir plywood (moderate stiffness as plywood goes), 16" is standard. You will notice flex as you walk on 20" spacing and you will be bothered by 24" spacing.

This flex I am describing is the surface skin flex and not the overall flex of the 1x2 M platform. The stiffness of any material is proportional to the third power of thickness and inversely proportional to the fourth power of length. Therefore, the 1 M dimension of your platform will be 16 times as resistant to bending as the 2 M dimension. So, given a panel that is symmetrical in its stiffness in both dimensions, all you need to design for and if you like, to test, is the 1M span.

If you can work with wood as well as steel then here is what I would do. Fabricate your tower from steel with an upper rectangular frame fabricated from 3" x3" steel "L" channel. Fabricate the 1 x2 M panel that will drop into this frame, out of wood. Use two, 3/4" plywood skins separated by six, 1 1/2" x 1 1/2" x 1M long, parallel spacers fixed to each skin with both construction adhesive and short, flat head screws driven through both plywood skins into the spacers. This panel will weigh a little over 100 lb and be plenty stiff. It will sit proud of the "L" channel by the thickness of the steel (say 1/8"). You can save 10 pounds in weight if the bottom skin is reduced to 5/8 thickness and be nearly as stiff (3 cubed vs 2.875 cubed) and sit flush into a 1/8" thick "L".

[Maltes]

All very good advices, I now know where to begin and what to do. Thanks every one.