Constructing a weight-bearing girder set piece

We're staging David Ives' Mere Mortals and I've been tasked with constructing a mock steel girder, about 8' in length, that can support the weight of three people but still be moveable. I wondered if anyone had any suggestions for how to go about it.
 

egilson1

Senior Team
Senior Team
CB Mods
Premium Member
12” x 8’ stick of truss with a Luan surround attached to it for the look of a beam.
 

Crisp image

Well-Known Member
Timber "I" Beam that is used for floor joists could be the go. Put 2 together and paint it up.
 
Combining people's suggestions, I’m thinking about something like this, from 3/4” plywood, with 2x4 internal supports. Glued and screwed. Add some fake bolts and a convincing paint job and I think it should do. Thoughts?
8E946C3B-3D85-4A99-9624-AC670A6B5030.jpeg
 

Amiers

Renting to Corporate One Fixture at a Time.
Kids/performers are going to want to flop on and off that sitting position and it will be more than 3 in rehearsal if kids are around. I would reinforce the top plywood with whatever flavor of angle you prefer.

Or adjust your design to make the center a triangle to the top and do you shadow and highlights with paint to make it seem flat.
 
Kids/performers are going to want to flop on and off that sitting position and it will be more than 3 in rehearsal if kids are around. I would reinforce the top plywood with whatever flavor of angle you prefer.

If it needs further bracing, I have plans to run vertical stiffeners on each face. I want to see how stiff it is when built, first.
 

Crisp image

Well-Known Member
If it needs further bracing, I have plans to run vertical stiffeners on each face. I want to see how stiff it is when built, first.
2x3/4 at 18" will not bend over that span. I would even consider 12" high but if it is the look you are going for go 18" Lateral forces are what you need to brace for. If your top and bottom chord are out of 3/4 ply and well fixed there should be no need for much internal bracing. A question for you is how is this to be suspended and how are the cast to be hanging from it? That may make the design different.
Regards
Geoff
 

Amiers

Renting to Corporate One Fixture at a Time.
2x3/4 at 18" will not bend over that span. I would even consider 12" high but if it is the look you are going for go 18" Lateral forces are what you need to brace for. If your top and bottom chord are out of 3/4 ply and well fixed there should be no need for much internal bracing. A question for you is how is this to be suspended and how are the cast to be hanging from it? That may make the design different.
Regards
Geoff


Maybe there was some misunderstanding I’m not talking about the beam snapping in 2 but more so the lip of the plywood overhanging from the vertical “beam”
 

gafftapegreenia

CBMod
CB Mods
Combining people's suggestions, I’m thinking about something like this, from 3/4” plywood, with 2x4 internal supports. Glued and screwed. Add some fake bolts and a convincing paint job and I think it should do. Thoughts?View attachment 22965

I'd sit on it. 👍
 
2x3/4 at 18" will not bend over that span. I would even consider 12" high but if it is the look you are going for go 18" Lateral forces are what you need to brace for. If your top and bottom chord are out of 3/4 ply and well fixed there should be no need for much internal bracing. A question for you is how is this to be suspended and how are the cast to be hanging from it? That may make the design different.
Regards
Geoff
We’re just going to span the space between two black boxes. We may put a lifting strap for show, but it will not be load-bearing.

Maybe there was some misunderstanding I’m not talking about the beam snapping in 2 but more so the lip of the plywood overhanging from the vertical “beam”
I understand that. I meant I would add 2x3 or 2x4 supports outside of the beam, simulating a plate girder like this: https://images.app.goo.gl/cNTxWFrAP6wQFAGj7
That said, I don’t think it will be necessary if I secure the top and bottom with construction screws and glue. A 6” overhand with 3/4” plywood is pretty sturdy. If I do need to add support, I can probably get away with just adding them on the back.
 

Crisp image

Well-Known Member
We’re just going to span the space between two black boxes. We may put a lifting strap for show, but it will not be load-bearing.


I understand that. I meant I would add 2x3 or 2x4 supports outside of the beam, simulating a plate girder like this: https://images.app.goo.gl/cNTxWFrAP6wQFAGj7
That said, I don’t think it will be necessary if I secure the top and bottom with construction screws and glue. A 6” overhand with 3/4” plywood is pretty sturdy. If I do need to add support, I can probably get away with just adding them on the back.
All makes sense now. Another question I have is with that construction how is it to be moved? Is it onstage all the time or will cast or crew have to move it? It will be quite heavy and at 18" high that is about the height of a standard seat height of a chair, then if you are going to put it on boxes is that so the cast legs can swing and give the illusion of being at height?
I would be interested in seeing the final result on stage. Keep us updated.
Regards
Geoff
 

Van

CBMod
CB Mods
Premium Member
You could simply use an LVL or TGI, LVL will be much heavier, and sandwich the web with Luan or Masonite for a smoother steel look surface. Add a top and bottom 'Flange' out of a couple layers of 1/2" ply <oriented and 90° to each other> ( I mean cut a 8'x 18" wide strip the length of a sheet and screw it in place on top of the TGI. Then cut a 48" long 18" wide across the ply and glue and screw it in place. The resulting strand orientation will be much stiffer than two layers of everything running long, stagger the seams) . The add little 1/2" gussets every 2' or so below the top and above the bottom flange, like in that picture, to add a bit of with support for the flanges. Something like this? <Sorry had to raw it in bluebeam.>
 

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Crisp image

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Looks good. Well built. I look forward to seeing it in situ.
 

Crisp image

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Looks like the real thing Nice work.
 

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