# Load Ratings for Platforms



## E52tech (Mar 8, 2012)

I'm putting together a set of platforms for an upcoming production. The platforms I inherited from past productions are standard 4x8 jobs ( 3/4" ply lid, 2x4 pine framing) with 2 evenly spaced toggles in the middle. My upcoming show involves loading 4 persons per platform (I'm using a 200lb person as a standard for all my calculations) with some moderate dancing. Because of the number of persons per platform, the height of the platform (6 feet) and the potential for significant live loads, I want to beef up my existing platforms and/or build better platforms. So here are my questions:

>What is the current load rating of my platform? 

>I have been quoted that an anticipated load rating of 200-250 psf is necessary for platforms with live loads associated with dancing. For a load rating of 250 psf, how beefy would one build a platform?

>To transmit these loads to the ground, are compression legs acceptable or do I have to move up to a studded knee wall?


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## mstaylor (Mar 15, 2012)

I don't know a formula but that riser should easily carry four dancers. What you need to worry about is the legging and bracing, that is your failure points.


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## Footer (Mar 15, 2012)

You will also find that there are two very different formulas used for scenery. One makes sure the platform won't fail... and yours is not going to fail. The other one makes sure it does not deflect enough for the human eye to detect it. The second one is usually the one we aim for. L/360 is the standard. You can go beyond that if its a heavy dance show. 

You can add more legs and that should make everything more solid. You can also run a piece of channel iron down the entire underside and that will really beef it up. Without knowing exactly how your platforms were constructed, how long they have been in use, and their current state there is no way to really figure out their loading capacity.


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## gafftapegreenia (Mar 15, 2012)

I thought standard was 3 toggles? A toggle at every 2 foot center.


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## Van (Mar 15, 2012)

gafftapegreenia said:


> I thought standard was 3 toggles? A toggle at every 2 foot center.



Honestly I've seen both, for standad platforming either is acceptable. On heavy duty platforms standard 16"oc is the norm and for Audience risers 12"oc with 2 layers of 3/4 B/C is code < In this town> 
Again I think Footer Nailed it. the platfor will be fine. it's all about the legs and then it's all about the bracing for lateral movement. If you are having dancers on a platform 6' in the air you have to remember that the leg is acting like a fulcrum for the lateral forces. So If I weigh 150 pounds < in my dreams> and do a shuffle ball change to the right then that 150 pounds will get a momentum behind it even at slow dance speeds this will result in significant Newtons. Not add the 6' of height and you've just multiplied the foot/newtons by a factor of 6 ! Needles to say you are talking about very significant loads moving laterally. This is why Handrails must meet such high standards in standard construction, one person can generate a lot of force. < Some of us more than others. 

Here's a handy bit of info. You might find it useful, you might find it confusing, but I like it! 

http://www.tecotested.com/techtips/pdf/tt_plywooddesigncapacities


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## derekleffew (Mar 15, 2012)

Van said:


> ... Again I think Footer Nailed it. ...


Calling Dr. Freud... 
I thought Nailer Footed it.


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## derekleffew (Mar 17, 2012)

Stage collapses during children's play in Folsom | 6abc.com


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## Footer (Mar 18, 2012)

derekleffew said:


> Stage collapses during children's play in Folsom | 6abc.com



This my show a bit how I think, but that sounded like a start of an onion story. 

Sent from my Galaxy Nexus using Tapatalk


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## derekleffew (Mar 20, 2012)

Update: 'Seussical' set accident at Ridley Community Center sends three children to hospital, stuns audience - Ridley Town Talk - Delco News Network :

> The set platform, which was built by a licensed contractor, was elevated four or five feet when a left-sided support gave way, sending seven young actors sliding to the stage floor below the platform before the watchful eyes of a stunned audience, police Detective Lt. Scott Willoughby said.


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## gafftapegreenia (Mar 20, 2012)

"built by a licensed contractor" 

So many questions which I know the media will never get an answer for, and so much Union bashing in the first article linked.


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## bobgaggle (Aug 24, 2018)

I know i'm necroposting, but i remember reading this thread and the articles about the stage collapse when I was working in Alabama back in 2012. Now today I'm doing a search on load ratings, come across this thread and realize I live 3 minutes from that community center now. I'll have to ask around and see if anyone remembers this happening. Anyway, do your math everyone and stay safe!


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## Diggits5 (Aug 30, 2018)

Hey All,

Adding to this post, does anyone know of an online calculator or PC program that can calculate load bearing capacities for steel constructed platforms? We have these on our stock and I'd like to know how many elephants they can hold. Thanks!


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## Van (Aug 30, 2018)

Diggits5 said:


> Hey All,
> 
> Adding to this post, does anyone know of an online calculator or PC program that can calculate load bearing capacities for steel constructed platforms? We have these on our stock and I'd like to know how many elephants they can hold. Thanks!


I don't know of a program but to accurately compute the load rating you will need to know the wall thickness of the steel as well as the welding size and placement.

Just looking at the layout I'd guess the plywood would fail before the truss framing would.


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## bobgaggle (Aug 30, 2018)

Van said:


> Just looking at the layout I'd guess the plywood would fail before the truss framing would.



Ha I was just thinking that. For how beefy the framing is, you went light on the decking...


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## kicknargel (Aug 30, 2018)

I wouldn't say light on the decking. 3/4 ply is super standard and appropriate to transfer the load to the frame. Sure, if this were sitting on the floor, the ply would fail first. But it's likely to be on legs. The total rating would depend on leg spacing among other things. 

The actual answers can be found (although not simply) in:
https://www.amazon.com/dp/024080354X/?tag=controlbooth-20


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## BillConnerFASTC (Aug 30, 2018)

Structural framing is not simple and when you introduce trusses, it's less simple and different. I'd guess diggits platforms are safe for any foreseeable load, doesn't mean the legs are.


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## Diggits5 (Sep 2, 2018)

Thanks all. We use 4x4 steel in the corners. The boss likes the span of these platforms without the need for supports. I'm actually in the process of consulting an engineer on calculations but we'll see if anything comes of it.


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