How can I elevate a platform safely?

September 5, 2008 1:15 PM

StageCraftFilter / EngineeringFilter. What is the best way to safely elevate a 4' x 8' rigid platform (theatrical) to about five feet from the stage? Currently, I have it situated atop four 4x4 posts, each five foot tall, each at a corner, bolts through the frame of the platform and the post. The posts are connected by 4' long 2x4s in front and back (about halfway down), and 8' long 2x4s on either side (halfway down). This works, but only just. It is not stable. I'm not putting an actor on a wobbly platform. So what else should be done to stabilize this contraption?

I have had several ideas, up to and including some kind of tension wire system (!), but time is of the essence and I'd rather call on experience than experimentation.

Oh, and I should mention that this needs to be built in a way that allows the platform to be removed from the "stands" after each night's show and restored before each show.

posted by grabbingsand to media & arts (14 comments total)

Triangles are the strongest shapes for this application. You can use cables-n-turnbuckles diagonally between the legs or you can run lumber stringers. The stringers will be stiffer, but since you have a skirt around the legs about halfway down, you might get by with cables.
posted by stubby phillips at 1:19 PM on September 5, 2008

Diagonal bracing can be very effective for platforms, and you can design the sides to fold up, with the top portion sitting on top of them for easy removal.
posted by markblasco at 1:20 PM on September 5, 2008

Basically each side of the stand would look like a capital N. Or an X if you're into belt-and-suspenders. (no pun intended)
posted by stubby phillips at 1:22 PM on September 5, 2008

X-bracing via cables, turnbuckles, and hooked bolts, as mentioned by stubby phillips. Going with cables will be more collapsible than using lumber. Lighter too. Also reusable. Personally I'd go with X for maximum stability, but I'm paranoid that way.
posted by aramaic at 1:28 PM on September 5, 2008

To add to what others have said, if the platform needs to be removable, you can build a square frame at the top of the legs that sits inside of the platform when it is installed. Have it fit snugly against the platform frame and hold them together with bolts and wingnuts. You could probably do the same thing without the frame (bolts through the frame to the legs with wingnuts) but the leg assembly may be a bit unstable when the platform is not installed.
posted by backseatpilot at 1:30 PM on September 5, 2008

Yes, you need diagonal (x'd) braces rather than straight across ones. If you use straight-across braces, the whole structure can still tilt like a parallelogram and collapse. If you use diagonals, that can't happen unless the "opposite" support compresses into itself, which is not bloody likely.

And/or: 8 feet is a rather wide span to only have posts at the corners. It might be easier for you with six posts (two in the middle) instead of four.

An even better and more portable solution might be some premade tubular steel "scaffolding supports" of the type painters use. They have all the diagonals and such built in, and are usually made PRECISELY to hold a 4x8 sheet on top. If you can't find these at one of those home superstore type places, call any painter and ask if you can buy some of their old ones for $20.
posted by rokusan at 1:38 PM on September 5, 2008

in addition to what rokusan said you can can always cheaply rent scaffolding depending on your needs time-wise. Often times I would rent scaffolding not for the platform etc but just to use UNDERNEATH the structure (just as suggested...)

-c
posted by chasles at 1:52 PM on September 5, 2008

The simplest way I can think of is to skirt the spaces between the legs with sheets of plywood. If it doesn't have to be collapsed for transport you could probably get away with cutting a couple of 4X8 sheets lengthwise, and you'd have enough to make a 2' wide band around the middle. If it feels sturdy enough, glue it and re-screw. Stagger your screws and put them 4" apart.
posted by bonobothegreat at 3:14 PM on September 5, 2008

bonobo's suggestion, even though it seems rectangular, is also a triangle-based solution. Each screw forms a triangle with every pair of screws on the opposite side.

The plywood would not have to be very thick. It's job is to resist stretching and compressing. The 4x4's give you the strength to hold up the platform (2 more would be ideal, as rokusan pointed out). The apron keeps the 4x4's from splaying out or in. All this solution needs to do is keep the 4x4's from all swaying in parallel.

You might consider moving the apron down towards the bottom, however. That would reduce the splaying on it.

All in all, if you can pull it off, the scaffolding solution would be the awesomest, especially if you can buy 'em cheap and use them again in subsequent productions. One "bucka scaffle" is all you need.
posted by stubby phillips at 3:45 PM on September 5, 2008

The cheapest and fastest solution, however, would be to buy 4 10 foot 1x3'x and nail them in a diagonal pattern like Charlie Brown's sweater. You'll have to trim them to about 9 and a half feet.
posted by stubby phillips at 3:58 PM on September 5, 2008

Basically each side of the stand would look like a capital N.

Only if you use a rigid member, like a wood stud, that can act in both tension and compression. Cables are strictly tension-only.
posted by LionIndex at 4:17 PM on September 5, 2008

Rent a Scissor Lift.
(like http://www.genieindustries.com/gs-series/index.asp)
posted by the Real Dan at 4:17 PM on September 5, 2008

If the sheets go on all four sides (and there's a top panel) it can't sway. Just be sure that the sheets go right to the outside corners (covering all the available 4X4 post) so that it has a solid grip on the post. Stubby' is right that you don't need thick plywood, but if you use thin stuff, be sure to glue 4" wide strips to the vertical edges to give it a double thickness along the posts so that the screws are going through something solid. I would stay away from 1/3's because if it wiggles around, there's a good chance that one or more will split where the screw-holes are, possibly leading to a cascading failure. I still think middle height is the best spot. I'm not an engineer, but I build a lot of stuff out of 2X4's and plywood. GLUEING the plywood to the posts will make it mUCH more solid. I would
posted by bonobothegreat at 4:19 PM on September 5, 2008

How to Build a Platform, written specifically for stage. I use this guide every time I direct a show, and even better, the genius who wrote it practices his craft at my theater.
posted by ewagoner at 7:37 PM on September 5, 2008