Building long unsupported spans

12" aluminum truss would be my suggestion. For a 16' platform you'd have a 14' span which would have a UDL of 2941# or PL of 843# for each truss.

Safety, as everyone else has pointed out, is number 1 priority here. Personally I'd laugh at your director and say no, too dangerous then suggest something else while keeping to his ideas to make it seem like hes still getting what he wants. I'd suggest a truss structure to a spec that you know will hold the weight at least 3 times over especially if they want to dance on it. Yes it will look ugly but you can then always make a vaneer face out of ply or hard board and bolt it to the front to hide it, best of both worlds then and no-one *touch wood* gets hurt

Thanks for all your replies! That was a ton of really useful information. Fortunately the set designer was persuaded to edit his design to something much less ambitious and dangerous, but I appreciate all the input.

Took a while to find this picture, but it shows two runs 12" box truss to span 20'.
"Lysistrata" by Aristophanes
Directed by Don Brady - Loyola Threatre - Fall 2004

Here is a span of at least 40', not the DJ booth.

quick question... How did the DJ get there, and how does he get down in an emergency?

DuckJordan said:

quick question... How did the DJ get there, and how does he get down in an emergency?

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And where is the support for the truss legs? Looks like 50 lb floor bases only. Hope the DJ doesn't jump too much!

DuckJordan said:

quick question... How did the DJ get there, and how does he get down in an emergency?

Click to expand...

Exactly what I was thinking. While this looks AMAZING, its not viable in a RWS (real world scenario). Too many variables to judge accurately (heights of people in the picture, angle of image etc) but the booth looks to be 15-20 footin the air, enough to break a bone if there IS/WAS an emergency and only resort is to jump

DuckJordan said:

quick question... How did the DJ get there, and how does he get down in an emergency?

Click to expand...

Rope ladder.

Synergetic Sound and Lighting is a nation wide event production company that has been a client of my since their humble beginning.

A closer look does reveal diagonal bracing up in the air between the truss and the legs. Okay, better. And yes what a wild concept!

Hello all. I'm building a stationary set and would like to have a 16' span center stage with a platforms coming off both sides. I have found This span table from This Manufacturer .

I want to make sure I am reading this table right. By my translation, I will be good to build a 4' by 16' platform using 5 of these 2" x 12" on 12" centers. Also, I could step down to 2" x 10" if I make the bridge 2' shorter.

Am I reading this correctly?

Also, If I use 2 x 12 I plan to bolt a 4 x 4 leg to each joist, cross brace them to each other and bolt them to the adjoining platforms.

If I use 2" x 10" my plan would be to have one foot of each side of the bridge overlap on top of the other platforms and have the bridge be a step up from the adjacent platforms. Then I would reinforce the legs on the platforms that are taking the extra weight.

It is very important to me that I am doing this safely and setting a good example for my students, so please let me know if you see any holes in my reasoning.


p.s. I do have a couple of calls in about rental pricing on truss, but if this is more cost effective and just as safe, then I would prefer to work with wood as that is where my experience is.

TheaterEd said:

Hello all. I'm building a stationary set and would like to have a 16' span center stage with a platforms coming off both sides. I have found This span table from This Manufacturer .

I want to make sure I am reading this table right. By my translation, I will be good to build a 4' by 16' platform using 5 of these 2" x 12" on 12" centers. Also, I could step down to 2" x 10" if I make the bridge 2' shorter.

Am I reading this correctly?

Click to expand...

Looks good to me.

TheaterEd said:

Also, If I use 2 x 12 I plan to bolt a 4 x 4 leg to each joist, cross brace them to each other and bolt them to the adjoining platforms.

Click to expand...

At 12" spacing, I'd make this a stud wall with 2x designed to line up directly under the joists. Sheath the stud wall to take care of lateral bracing in the US/DS direction. Bracing between 2" x 12" should occur at supports as well as some mid-span (I might go as often as every 4' along the length).

Be sure your support for the adjacient platforms and connection to the adjacient platforms is sufficient to transfer cross stage latteral loads. Alternatively, if the design allows, the stud wall under the bridge could be braced in the cross-stage direction under the adjacient platform.

Don't forget, sizing of your vertical supports depends upon height and bracing.

TheaterEd said:

If I use 2" x 10" my plan would be to have one foot of each side of the bridge overlap on top of the other platforms and have the bridge be a step up from the adjacent platforms. Then I would reinforce the legs on the platforms that are taking the extra weight.

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This sounds like you'd be cantilevering out the adjacient platforms to support the bridge. This could work, but I'd caution you to have an expert analyize the specifics of this design. It's easy to miss an important detail as the structural support becomes more complex.

So after having the extended weekend to think this through. I'm planning on using five of the 16' 2x12 and supporting them with 2x4 stud walls sheathed with ply. I'm thinking that I will use 4x4s for the end supports on the stud walls so that I can run a bolt through them to attach them to the adjacent platforms.

The regular platforms are about 70" high, so I will plan for the top of the bridge to be around 78". This should give me enough clearance underneath the bridge and add some more levels for the director to utilize.

Let me know if I'm missing anything.

TheaterEd said:

I will plan for the top of the bridge to be around 78". This should give me enough clearance underneath the bridge and add some more levels for the director to utilize.

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Your plan for support sounds good. If the bridge deck is at 78", that only leaves about 5'6" clear under the bridge - not much space for creating additional levels directly under the bridge unless all you actors are short.

robartsd said:

Your plan for support sounds good. If the bridge deck is at 78", that only leaves about 5'6" clear under the bridge - not much space for creating additional levels directly under the bridge unless all you actors are short.

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Well, we haven't cast the show yet, so I will keep that in mind

My instinct is that - if the platform can be masked below - this will be best achieved with the assistance of some local friendly scaffolders. Ladder beam and decking on top and you should have a 16' wide platform suitable for dancing on, that will take the weight fine.

One thing to be aware of - 4' is not deep at all for something with an open front (and back?!) . For dancing 8' in the air, you will really have to consider your edge protection to stop anyone coming off it, a fall from 8' will be serious if not fatal. In today's world, simply 'watch where you put your feet' is not enough.

de27192 said:

My instinct is that - if the platform can be masked below - this will be best achieved with the assistance of some local friendly scaffolders. Ladder beam and decking on top and you should have a 16' wide platform suitable for dancing on, that will take the weight fine.

One thing to be aware of - 4' is not deep at all for something with an open front (and back?!) . For dancing 8' in the air, you will really have to consider your edge protection to stop anyone coming off it, a fall from 8' will be serious if not fatal. In today's world, simply 'watch where you put your feet' is not enough.

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There will be front and back railings.