So while Justin Lang (editor of PLSN) was off participating in the “There’s a Lighting App for That” panel, I headed over to the “Platforms Revisited: A Discussion of Stock Platforms” panel. The panel was chaired by Heather Hillhouse, with Mary Black, Scott Mollman and Ted Tysinger. The question they put themselves to was: What do we really know about the stock platforms we use daily? They wanted to examine decking options, framing options, cost, durability, etc.

First they presented a standard platform analysis, comparing 4x8 foot platforms with ¾” CDX plywood. Let’s dive right in!

2x4 frame w/ CDX plywood
avg cost $31.42, including 2x4 and plywood, not including incidentals.
Strength 118 lbs / 4x8, 60 psf live load. Weakest test was bending for center toggles as 4’ beams.
Pros: inexpensive, strong, easy to build.
Cons: weight.

1x6 frame with CDX plywood.
Average cost, 34.29
Weight 108 lbs
Will support 52 psf live load.
Pros: if ripped to 5/14” creates even 6” platform height, slightly lighter than 2x4 frame
Cons: a little less durable.

1x2 16G steel, with ¾” cdx ply deck
avg cost – 49.34, but very strong, supports 71 psf live load.
Pros: very durable
Cons: add’l skills to construct, cost.

Ply wood frame, w/ ¾” CDX ply deck
Can’t really analyze structure, b/c design values for this not supplied in this size

Next, tackling triscuits. Using 5/8 CDX top and bottom, with 5/4 lumber.
Building at 3’11 7/8”, so can get two out of one sheet of ply.
Pros: very small, 4x4’, so easy to store, and lightweight. One person can handle one. And easy to install. They are also very quiet. B/c 1/8” shy of 4x4, you leave 1/8” between them when installing, so you lose squeaking between platforms.
Cons: They require studwalls to install, and you’re more than likely building studwalls for each production. They take more time, effort and skill to build. This is also less common lumber. Finding 5/4 lumber a little harder to come by. So this becomes a little more cost prohibitive.

Triscuit – ¾” ply on both sides, with ¼” material as structure material
A little more common materials. Avg cost - $50 for 2.
A lot of the pros and cons are the same for this as for the previous triscuit, but the lumber on this one a lot easier to find.

Cheapest frame to build is the 2x4 frame w/ 3/4” CDX ply
Lightest is also the 2x4 frame w/ ¾” ply [UPDATED: panel chair Heather Hillhouse wrote in to correct me that the 1x6 frame was the lightest, though "not by much."]
Triscuit with ¼ frame had best structure, but the 2x4 w/ ¾” ply was right in the middle.

So with all the data – what surprised us?
Structural benefits of triscuits were surprising.
Also, prices on everything (Except the steel was surprising.)
Triscuits are easy to use, once you’ve gotten past start-up costs. Then challenge becomes customization, making things match.
Of course, triscuits are a challenge to build, especially when building customs.
But 2x4 platform still seems to be standard.
Come up with standard bolt pattern, so you’re not drilling in everywhere. Really helps on wear and tear.
If you’ve already got a standard, hard to move onto something else.
A lot of pros and cons were just anecdotal, so they’re opening up to questions.

Labor estimations on how long it takes to actually build each style?
They decided not to do those studies, b/c they didn’t have time or money to build multiple platforms and truly study. So it all comes down to anecdotal—b/c can’t control time of day, mood of crew, fasteners, etc. Too many variables. In terms of cuts, triscuits have way more cuts and fasteners, so will require more time.

Someone saying using ¼” ply on the bottom of a triscuit doesn’t cut down on durability, cuts down on weight.

So what do these figures mean? 60psf? What’s that?
Panel says that 50 psf should be sufficient.

Disadvantage of triscuit is that structure is integral to install orientation. Have to make sure they’re going onto studwalls in correct orientation.

Studwalls every 2 feet means you could put ply right on top of it, like straight decking, but then challenge becomes the seams and point loads.

Didn’t consider any sort of sound damping – can fill triscuits with foam, or coat bottom of platforms with different materials, but didn’t consider in strength tests.

Did anyone consider parallel platforms?
People do if they have it in stock, but they didn’t analyze – but generally it’s a ¼ frame, so can infer it will support less. Easier when platforms all at same height.

How do you deal with squeaking between platforms?
Put in more screws, or bolts, or fasteners of choice. Tar paper can also be used, but it can be a pain with little payoff – so just add more fasteners.

Full presentation will be posted on technical commission website. I’ll try to download that. I’ll also get the video I took of the presentation posted as quickly as I can.

Tags: USITT, decking, platforms, plywood

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Replies to This Discussion

Hi Jacob-  Thank you for posting your summary, and particularly for capturing the discussion which was very valuable. I'll post here as soon as the presentation is posted on the tech commission website, although I can email it to you directly if it would be easier.   One minor correction-  the lowest weight platform was the 1x6 frame , but it wasn't by much. 

Heather Hillhouse

Thanks for writing, Heather! If you could e-mail me the presentation, that would be easiest -- jc (at) stage-directions (dot) com. I'll also edit to make the change about the weights.
Heather: There's a pretty extensive article about platform designs, similar to what it sounds like your presentation covered, in TD&T, Spring 2008 (volume 44 number 2), which I wrote. I didn't touch steel-framed platforms, and I think some of my stress analysis numbers are a touch off, but overall, there's a good discussion of the merits of plywood, 2x4-framed, stressed-skin and sandwich core, from the perspective of time, labor, storage, reusability, cost, etc. I wish I'd been able to see your presentation! I'd love to find time to chat with you about this, though--it's a fascinating subject!

Heather did send along the presentation in PDF format -- ultimately I would like to include it as a slideshow, but for now I'm attaching the file so people can download it if they like.

 

 

Attachments:
JACOB!!! You ditch my session!?!  Here I thought that was you in the back leading off all the laughing at my jokes!  I guess it is a good thing I recorded the session. ;)
I have built a lot of plamforms using 5/4 framing. you can buy it at 5/4 or buy 2 by framing and plane it to 5/4". L  and T irons morticed and screwed to the framing on the side opisite the plywood will make these units stronger and more durable. We have used casket locks, aka turn locks, in a specific layout with males on two adjacent sides and females on the other two sides. This allows platforms to be joined without any drilling.

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