# dead hung lift line spacing and unistrut questions?



## jds10011 (Nov 16, 2018)

First, this isn't a "I have a dumb idea to making things fall on people" thread; just looking for resources to hand to a structural engineer who isn't too familiar with theatre. Not planning to rig anything without his stamp.

Question 1: I've been told some hand-wavy numbers about spacing on lift lines for dead hung battens (some for boring things like legs, some for more exciting things like electrics). I've generally heard 8' is safe and 10' might be ok. Are there any good sources I can point to? (He would like 3'...) Naturally, we plan to use 1-1/2" schedule 40 "gas pipe", with batten splices where appropriate, probably in 20' lengths.

Question 2: Also, this space will involve entirely dead-hung battens, with the possibility for expansion or at least movement later. The only access to the ceiling will be via scaffold (or lift). There are structural beams running SL<->SR above the stage, which our engineer plans to specify attaching to. The only place I've worked that has done this has used unistrut running upstage-downstage, structurally attached to the beams, with the channel facing down, with rated eye bolts mounted on unistrut mounts that are then attached to shackles and finally lift lines. Even though the plan is that you can loosen the eye bolt, slide the mount along to the desired position, and re-tighten it, to my mind the possibility of doing that under load without realizing it or of not tightening it appropriately or in the proper orientation is mind-boggling. (Disclaimer -- this setup also came with an engineer's stamp of approval -- were I the engineer, I shouldn't think I'd stamp it, and I don't recommend you use this setup.) Obviously I've worked plenty of places where I-beams were installed upstage-downstage in the appropriate locations and enormous beam clamps were used for the lift lines, but this appears to be orders of magnitude more expensive, not to mention that we need to subtract the weight of the new beams and hardware from what we'll be allowed to eventually hang. Could anyone point to some good resources that I could give the engineer on this subject? (I'm also secretly hoping there is a product like unistrut where the mounts don't just fall out if you're careless, or a magical circular unistrut mount that's a pain to install but doesn't actually fall out when it's a little loose -- I've seen safer systems for track lighting in office ceilings.) And yes, I understand that the sleepy or the careless shouldn't be doing rigging, and that a sufficiently sleepy or careless person can make anything fall on anyone regardless of design; it's just that the unistrut system seems so questionable that it keeps me up at night, especially since I've definitely worked with reasonably experienced people who are unfamiliar with unistrut and are floored by the fact that the little piece can just come right out -- what about the day I'm not there to tell them? (Unistrut isn't a super-theatrical item, either, so saying "use trained people" doesn't always cover it...)

Thanks, and again, please understand that I'm not trying to ask questions that I shouldn't on this forum -- a nudge in the right direction toward a standards document and/or some manufacturers is entirely ok. Advance apologies if I've said or asked something I shouldn't.


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## The Grid is Iron NY Frank (Nov 16, 2018)

jds10011 said:


> First, this isn't a "I have a dumb idea to making things fall on people" thread; just looking for resources to hand to a structural engineer who isn't too familiar with theatre. Not planning to rig anything without his stamp.
> 
> Question 1: I've been told some hand-wavy numbers about spacing on lift lines for dead hung battens (some for boring things like legs, some for more exciting things like electrics). I've generally heard 8' is safe and 10' might be ok. Are there any good sources I can point to? (He would like 3'...) Naturally, we plan to use 1-1/2" schedule 40 "gas pipe", with batten splices where appropriate, probably in 20' lengths.
> 
> ...


Please Hang off the grid correctly not off of bolted attached nothing don't scare me just joined this site today


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## RonHebbard (Nov 16, 2018)

jds10011 said:


> First, this isn't a "I have a dumb idea to making things fall on people" thread; just looking for resources to hand to a structural engineer who isn't too familiar with theatre. Not planning to rig anything without his stamp.
> 
> Question 1: I've been told some hand-wavy numbers about spacing on lift lines for dead hung battens (some for boring things like legs, some for more exciting things like electrics). I've generally heard 8' is safe and 10' might be ok. Are there any good sources I can point to? (He would like 3'...) Naturally, we plan to use 1-1/2" schedule 40 "gas pipe", with batten splices where appropriate, probably in 20' lengths.
> 
> ...


 *@jds10011* A few thoughts for you: In Canada where I'm posting from, the virtually identical product is called Can-truss, sort of makes sense, UNI strut in the US and Can truss in Canada. 
In Canada I would find all the answers to spanning distances and loads well documented and detailed on the Can Truss site. 
I would also be told of at least four versions, cross-sections, and load ratings with full engineering details for every specific model. 
From memory, Can Truss is manufactured in a least four variations; thin (shallow), thicker (often thought of as normal), double truss comprised of two layers of standard truss spot-welded together back to back. There are also versions of truss with slotted holes running end to end. Our Canadian supplier purchased his truss in twenty foot lengths and would cut to any length specified at time of ordering. We often saved money by ordering our Can Truss in uncut 20' lengths and either cut it ourselves with a portable horizontal band saw in the back of a 16' or 20' truck or transported it full length if we had a 24' truck at our disposal. Google should be your friend for more design and span / support info' than you could ever need. I always found Can-truss EXTREMELY generous with their supporting documentation, they don't want to see you fail either. 
Toodleoo! 
Ron Hebbard


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## BillConnerFASTC (Nov 16, 2018)

You need to quantify the loads first - and if battens I use 30 plf - and am comfortable that is inclusive the batten, clamps, and hangers.

I use the Clancy Rigulator app, accept the basis, and use the 10'. 1 1/2 " pipe on 10' centers uniformly is shown good for 41 plf for bending and 36 plf for deflection. Point load the center and its 176 for bending and 126 for deflection. 

The unistrut sounds find - its probably better to use the P1001 - which is two of the 1 5/8 basic channels back to back - so open up and down. You just need to go through the calculations -which is why unistrut is popular because they have such good data easily available. 

If hangers at 10' or so on center to typical batten, hanger is easy and lots of options. If a pipe grid, you need to look harder at the tributary area.

I personally specify not using the sliding nuts but to through bolt and plate on top. Usually with all thread to pipe clamp, but eyes, turnbuckles, and wire rope can be fine and more practical - you don't mention how far below beams battens are to hang.

If you can set unistrut on beam flanges - so clamp is just holding to prevent sliding off - I think better. You could do that with pipes also - there are rated clamps for pipe to beam flange - and then use all chain. Not a bad option, simple, easy to calculate and install.

Lateral movement -sway - is perhaps a concern.

Direct answer to your first question - tell teh engineer 30 plf - or other - and point loads - and they can calculate the hanger spacing. You also need to specify a deflection limit - usually expressed as a ratio of span. I'm fine with 1:90; but I think Clancy uses 1:180 So from no load to full load with my 1:90 - basically it will deflect an inch and a third. 1:180 - just 2/3 of an inch. But that is at 30 plf - which is a lot - like a Source4 LED every 12". The point load is what will do that - the tarzan rope and actor swings on or someone lifting with a chain motor. But I don't have a problem with that much deflection. It won't fail.

Does that help?


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## jds10011 (Nov 16, 2018)

BillConnerFASTC said:


> You need to quantify the loads first - and if battens I use 30 plf - and am comfortable that is inclusive the batten, clamps, and hangers.
> 
> I use the Clancy Rigulator app, accept the basis, and use the 10'. 1 1/2 " pipe on 10' centers uniformly is shown good for 41 plf for bending and 36 plf for deflection. Point load the center and its 176 for bending and 126 for deflection.
> 
> ...


Very informative; many thanks. The only thing I was hoping for was a solution to allowing someone to fairly readily move a dead-hung batten -- this happens frequently for legs, which nearly everyone coming in wants to move upstage or downstage a foot for a variety of reasons. Through-bolting the unistrut obviously solves the safety issue but does not offer much flexibility (and I think we are in agreement that the sliding strut mounts are not a good plan, though I've seen it done.) The battens are only to be a few feet (maybe three at most) below the beams.

Thanks again!


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## bobgaggle (Nov 16, 2018)

jds10011 said:


> Through-bolting the unistrut obviously solves the safety issue but does not offer much flexibility (and I think we are in agreement that the sliding strut mounts are not a good plan, though I've seen it done.)



I don't think you have much more work. You just gotta bring a wrench with you up on the lift. The trade is a bit more time for a lot more safety...

Alternatively, since you anticipate moving these pipes a lot, you could rig two lines on each point on the pipe, one holds the load and the other is coiled up neatly. When you need to move the pipe, take your loose line, install it where you want on the unistrut, then back off the turnbuckle on the load line until your new point takes up the load. Put a sharpie mark or something on the turnbuckles so you don't have to measure trim every time.

Or you could buy/make some square nuts that can't fall out of the track. I don't use unistrut that much, so I don't know if they sell them, but you'd think there would be a option, albiet a seldom used one, for a nut that will always stay in there... Buy more than you need and slide 1 between each pipe position for the future haha


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## MNicolai (Nov 16, 2018)

jds10011 said:


> Obviously I've worked plenty of places where I-beams were installed upstage-downstage in the appropriate locations and enormous beam clamps were used for the lift lines, but this appears to be orders of magnitude more expensive, not to mention that we need to subtract the weight of the new beams and hardware from what we'll be allowed to eventually hang.



If you haven't already, ask your structural engineer and CM to ballpark a rough magnitude price each way. Beam clamps are cheaper than an intermediary strut grid if reorienting the beams the right way for a theater doesn't explode the cost of your structural steel. Depending on what the other structural elements in the room are, be they precast walls or steel columns, it may not be that expensive to reorient the beams. For example, you may actually be able to move to smaller beams if you orient US/DS, but would just have more linear feet of beams installed than if you went SR/SL.

From a loading standpoint, you may also want to point out to the structural engineer that the nature in which the rigging will be used will concentrate loads on individual beams if they are oriented SR/SL. You could have an entire electric loaded primarily on a single beam. Whereas if you orient US/DS, you get diversity of loads (curtains, electrics, empty pipes, etc.) on each beam so all of the beams will share the weight of the heavier battens.

FWIW, if you orient the beams the right way you can rig the battens to beam trolleys instead of beam clamps and move the battens whenever you like whenever you like. Even 1T CM trolleys are only $150/point. I'm doing a rehearsal hall now where they'll be doing this so they can hook motors wherever they want in a motor-down configuration while minimizing the amount of hardware people have to take up with them in single-man lifts. (The caveat to this is of course that most venues with this setup end up setting the trolleys where they want them and then never move them again for 10 years.)


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## bobgaggle (Nov 16, 2018)

MNicolai said:


> (The caveat to this is of course that most venues with this setup end up setting the trolleys where they want them and then never move them again for 10 years.)



Well, you can't ever get away from that. And inevitably the thing you design to never move is immediately in need of moving...


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## MNicolai (Nov 16, 2018)

@bobgaggle That's one of the unwritten laws of nature. "Newton's Fifth Law of Regret"


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## BillConnerFASTC (Nov 16, 2018)

Unistrut makes a fine trolley. Use that for the legs. The nuts in the track do not really "slide" nor are they meant to.

By all means if this isn't already built up and down stage beams. I thought these were existing.

I don't know enough overall about your stage, uses, spacing, but if this a a lowish dead hung space - you can work with 15 or 20 PSF over the stage as a basis - and that is very conservative. Just consider Iroquois Theatre when it burned had 167 linesets with scenery and it was under 10 psf. So good to be cautious and conservative, easy to go overboard.


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## RonHebbard (Nov 16, 2018)

BillConnerFASTC said:


> Unistrut makes a fine trolley. Use that for the legs. The nuts in the track do not really "slide" nor are they meant to.
> 
> By all means if this isn't already built up and down stage beams. I thought these were existing.
> 
> I don't know enough overall about your stage, uses, spacing, but if this a a lowish dead hung space - you can work with 15 or 20 PSF over the stage as a basis - and that is very conservative. Just consider Iroquois Theatre when it burned had 167 linesets with scenery and it was under 10 psf. So good to be cautious and conservative, easy to go overboard.


* @jds10011 @MNicolai @bobgaggle* and *@BillConnerFASTC* NEVER forget snow and water loads including when roof drains are plugged with leaves and the stagnant water is filled to the lip of the roof's parapet. 
Toodleoo! 
Ron Hebbard


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## The Grid is Iron NY Frank (Nov 16, 2018)

BillConnerFASTC said:


> You need to quantify the loads first - and if battens I use 30 plf - and am comfortable that is inclusive the batten, clamps, and hangers.
> 
> I use the Clancy Rigulator app, accept the basis, and use the 10'. 1 1/2 " pipe on 10' centers uniformly is shown good for 41 plf for bending and 36 plf for deflection. Point load the center and its 176 for bending and 126 for deflection.
> 
> ...


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## The Grid is Iron NY Frank (Nov 16, 2018)

RonHebbard said:


> * @jds10011 @MNicolai @bobgaggle* and *@BillConnerFASTC* NEVER forget snow and water loads including when roof drains are plugged with leaves and the stagnant water is filled to the lip of the roof's parapet.
> Toodleoo!
> Ron Hebbard


This is appropriate action and Vision. Thank you Bill and Ron, For leaving no question that I can trust things I am Working above or below that I can't see.


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## SteveB (Nov 16, 2018)

@Bill and Mike.

Thanks for your input on this thread, it actually answers some of the questions I asked in this thread:

https://www.controlbooth.com/threads/is-it-safe.44659

As I never heard back from the rigging installer on our system as to as-builts or was it signed off on, and as we started hanging units today, this was timely. 

This system is Roof Beams - Beam Clamps - 3/8” threaded rod - US/DS Channel Steel - Unkown Hardware - 3/8” Threaded Rod - ETC hangers/raceway/1-1/2” schedule 40 pipe

The lack of any lateral bracing is a concern, as Bill commented on and I’ve instructed NO side-arms and no yoked out units.


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## MNicolai (Nov 17, 2018)

@SteveB Find out who the architect was and give them a call. They should have copies of all submittals, RFI's, and correspondence. You're their direct client and they'll want to keep you happy. If something happened under their nose that their consultants missed during punch lists, they'll want to know themselves. They want to avoid litigation or risk as much as anyone.

Whereas the rigging installer is possibly 2-3 subcontractors deep from someone who has a direct contract with you. Their primary goal is to fulfill their contractual requirements, no less, and no more, and get out of dodge. Usually once it's installed it's hard to get anything changed unless it's an egregious breach of contract, but you should at least be able to get the whip cracked at all the right people to find out how you ended up with that strut grid, and how much it's reasonably safe to hang from it.


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## BillConnerFASTC (Nov 17, 2018)

Designing with Unistrut/Kindorf/Canstrut is fairly straightforward. The manufactures do this so the trades people in the field can design for field conditions.

Designing for changes like the moving legs is trickier. Just deteriming worst case is not always simple. Will someone push all the legs to middle of longest span?

On the legs, you might consider hanging a single up and down stage curtain track and hang legs on roto-drapers. This would allow both adjustment up and down stage, the option to pivot, and the ability to clear the stage by pushing them all against the upstage or downstage wall or edge.


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## mbrown3039 (Nov 22, 2018)

BillConnerFASTC said:


> I personally specify not using the sliding nuts but to through bolt and plate on top. Usually with all thread to pipe clamp, but eyes, turnbuckles, and wire rope can be fine and more practical - you don't mention how far below beams battens are to hang....[although] Lateral movement -sway - is perhaps a concern.



^^^ This. By using all-thread your sway is greatly reduced (as compared to wire rope), and all of this hardware is available at any professional hardware store (not Home Depot/Lowes, but the store where the local machinery/heavy industry folks shop). We also insist on double nuts on the top of the all-thread, with the top nut being a locking nut and no less than double the all-thread diameter of exposed thread when done. If you didn't paint it in the fist place, you can wrap your all-thread in black snakeskin to mask it. mike


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## jds10011 (Jan 14, 2019)

Apologies for reviving ancient threads, but I just wanted to let folks know that (not for exactly this application) City Theatrical does indeed make the "magical unistrut fitting" I'd been asking for above. http://www.citytheatrical.com/Produ...rs-?dept=f08878d4-186a-43b5-9499-62116fce6480


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## BillConnerFASTC (Jan 14, 2019)

Great piece but still not great for sliding. I wonder if it will work on the ETC Flypipe.


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