Leaning Wall Effect

[House913`]

Hey all,

I'm working on a production that wants a wall to slowly move from upright to 30 degrees so that it leans down stage. I'm approaching this by using high strength hinges that attach to a ledger board that is then lagged into our deck. We have an automated line set and my thought is to use the line set to control the angle. What I'm struggling to deduce is what force the line set would take from the wall. I can't seem to locate any of my rigging books (recently moved and its still a mess) to put me on a path, and even if I did, I don't think I'd be able to figure it out confidently. I've included a diagram to help explain my situation. Any help would be appreciated.

 

[TimMc]

Uh... don't do this with a 2,200 lbs wall. That 5 or more folks haven't jumped up to give formulae and numbers says this is a Really Bad Idea.

Also there is nothing to "stay" the line set; as the wall tilts the lineset will be pulled downstage which may create other problems overhead.

I'd look for another, much lighter way to build the wall, perhaps foam and luan, or rent a sonic welder and make an inflatable vinyl wall (or several sections thereof).

 

[House913`]

The thought I had was to saddle the batten off on both sides to the pin rail that exists on both sides of the stage, using said pins to ensure the rope/ratchets/GAC doesn't slide after its placed into tension. Another line set upstage would be the control batten for the movement.

 

[jtweigandt]

I'd hesitate to do this even with a 4x12 flat. 2200 lb is more the territory of hydraulics and draw bridges

 

[House913`]

The flat construction is 1x2 14 ga steel for this particular attempt at engineering this effect. The wall is 38 ft wide, covered in Luan and a layer of cardboard. Most of the weight is the the steel at 1050# and cardboard at 600#. This is not a construction process that is solidified or even confirmed. I'm just trying to get numbers and math done so that I can present feasibility to the design team given our budget and current capabilities.

 

[House913`]

Alright y'all, ready for some math time, because I found what I needed and I'm eager to be proven wrong so that I can learn and change my plan as needed.

The goal is to figure out what the static equilibrium of the wall at the 30 degree angle is. I need to find the moment around the pivot (x for our equations sake) at this position to find the horizontal force acting on what will be my rope (which is remarkably similar to the ladder leaning on a wall question in a statics class). I have switched my dimensions and weights into Meters and Newtons respectively for easier math. FF is traditionally the force of friction in this setup, but in this instance is the horizontal force the hinges experience (across the whole load of the wall) and I didn't feel like making up a new symbol for it.

Our moment of X equation for this point would be so: Mx=N2(H)=FL(.5L)
N2(4.818062)=9786(.5*2.7813)
N2=2824.5591069604 N = 635#

This would also mean that FF also equals 635#, as these forces would need to be balanced to prevent movement.

Now that I have that, I can use the reference table to find how my force my batten would experience as the rope goes around it for the 90 degree turn into the floor.

Resultant force = (Sin(90) * 635) / Sin(45)
Resultant force = 898.025612 # @ 45 degree angle

Now that I know the force acting on the batten, I can adequately decide if this is a feasible build or not. It isn't because I don't have a way to saddle multiple points across my batten and, once forces of acceleration are added for the movement of the wall back and forth, it supersedes the WLL of our automation system.

I am gonna steal the foam idea of @TimMc as I think that would reduce the weight enough to make this feasible, so long as the budget allows it.

References:

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Pg. 15 Stage Rigging Handbook

 

[jtweigandt]

my concern here, in all seriousness is that your calculation accounts for the forces at rest. Not the deceleration when it stops.. How fast is it moving? Is it totally smooth, or do you get a "jerk" that massively increases the load at the end.
You have the inertia of the moving wall to decelerate, and it makes a huge difference whether that happens over a foot or an inch.

Also if you go beyond 30 degrees.. the force rapidly increases.. What do you have in place to assure it can't go beyond 30 and rapidly increase the load. I'm just a Veterinarian for full disclosure, but the whole concept gives me the willies.

Figure the force needed to dead hinge lift from the floor, and I might consider standing under the thing.... if your rig can handle double that. I have made huge box beams from foam..and they were quite rigid... maybe frame AND wall could be made up from foam

 

[House913`]

The de/acceleration is not the smoothest on the system, so there will definitely be shocks as it moves. The system is only rated for 1200# and in an attempt to keep some sort of safety factor ( the aim was 1:5), the shock loads will be greater than what the system as a whole can hold. The sheer size of the wall is the largest contributing factor to this particular problem. The foam reduces the weight to 1127#, the force becomes 325# in horizontal and a resultant force of 458.25#. I could run the math for force at acceleration and deceleration, but I don't think halving it is still enough for me to do said math. Let alone creating a modular system to assemble the wall in space during load-in.

 

[TimMc]

It sounds to me like Herr Direktor needs a bitch slap upside the head a heart to heart talk with the producer, the producer's insurer, and the venue's board.

@House913` - the lack of participation in this topic by People Who Know Their Stuff® should be the first red flag here. Not just that they don't want to give advice or help with math, but that they fear any negative reaction of the load, personal injuries or deaths, or property damage to the venue would result in them being named in a lawsuit. CAREFULLY consider their lack of participation as them saying "this is a really, really, really, really, really.... did I say 'really'? BAD IDEA.

 

[TimMc]

I would instead refer the OP back to the title of this topic: leaning wall EFFECT.

We sell imagination to audiences who WANT us to tell them a story. I suggest that the audience be allowed to use their Gray Matter to bring them into the story. They're invested then, with a stake in the mental outcome. And all that is better than having seats full of witnesses when the proposed design fails.

 

[Rainmaker]

I could also be way off on your goals here but even for a wall 38' wide and 18' tall, you shouldn't be constructing it at anywhere near 2200# if this is the effect you're going for.

A 4x16 is ~100 pounds when made with luaun and 1by, 10 of those would be 1000. Still obviously heavy as all get out but a number much less intimidating.

I'm wondering if this effect is the big thing and the director isn't willing to compromise with some cool uplighting to make the shadows play onto the wall like it's starting to lean, why not build this from foamcore? Most theatrical suppliers sell 4*8 sheets that are about 5#. This makes your entire flat around 400# even if framed from 1*3 stock.

I'm still not gonna be the person to sign off on your math but there are ways to make the numbers and construction way less scary.

 

[House913`]

The weight is compromised of 1x2 14 GA steel, Luan, and a layer of 1/4" cardboard for texturing. The wall has to be composed of 4× whatever sized flats since we only have a box truck to move the scenery around. The weight breaks down to 1200, 400, and 600 lbs respectively for each of the materials.

The effect has been tabled for budgeting reasons, as the other components needed for the effect took away from other elements that were desired.

 

[bobgaggle]

lol now I'm trying to remember how we did this in college. Once "Twelfth Night" closed its run, the three walls were all leaned in and some other decorations changed and "Night Twelve" premiered. The reimagined work was not well received haha.

Anywho, I believe we use static lines to the grid to hold our angle, since it only moved during the changeover. If your organization decides your math is acceptable and decides to move forward, it wouldn't hurt to add some backup safety lines to your wall. they'll sit there all loose when its vertical and act as a positive stop when you lean it.

 

[Jay Ashworth]

If this wall really weighs a ton, and you do not have a licensed rigger, and probably also a certified professional engineer, sign off on these drawings, the theatre's insurance carrier will not cover it when it falls and kills someone; they will come after you.

Don't. Really.

 

[jtweigandt]

Kind of academic by now, but If I were charged to do this, I would use a regular flown in cloth painted drop. If the lean happened not real time but in a scene or intermission change, I would pull the foot back, bring the drop down the necessary amount, and anchor it to the floor rather than lean the top in

have 2 sets of spike marks and move all the furniture back accordingly as well. Will the audience say.. hey they're playing 3 feet deeper? nope.. Will they say hey the wall's leaning. yep.

But then since I'm from community theater, I've spent 23 years trying to figure out how do do fx on the cheap, and hopefully safely as well.

 

[kicknargel]

I feel the need to chime in with the old-timey way to make a lightweight wall: Broadway Flats. Not saying it would necessary work here, even if the project were still active.