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Author Topic: securing truss  (Read 23014 times)

Timoteus Ruotsalainen

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securing truss
« on: April 22, 2004, 01:28:57 am »

My friend had a truss fall. When they examined it they found out that one of the slings (on one side) had ripped and the truss swept (other side still attached) down. Some people were injured but nobody was killed.

I started thinking, if you cannot trust the slings to hold, is their a way to secure truss with extra slings, maybe to the roof (point where motors are rigged)? Also when is it appropriate to use security chains on fixtures? Is there a way to test these slings for failure?

Now I suspect that they might have had the slings fail because of abuse or careless use but I don't want to be the one that rigged something that fell. They said they pulled their whole inventory of slings out after this and used them to pull cars to test them.

--
Timoteus Ruotsalainen
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len woelfel

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Re: securing truss
« Reply #1 on: April 22, 2004, 07:27:12 am »

We call those spansets.  If you're using any rigging, you should have 2 different types of thing wrapped around at each point.  We use steel safety cables attached to the motors.  The spanset allows for a stable wrap so that the truss won't twist, and the steel safety won't melt in a fire (a spanset may), but doesn't allow for precise truss placement.  

VDI

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Re: securing truss
« Reply #2 on: April 22, 2004, 09:03:54 am »

 Shocked   Swinging truss?  a riggers nightmare.  DEFINITLY!!!  always use a steel cable backup. If you're using the yellow web slings, stop.  buy some good spansets.  there are some of a new type that have a multiple stranded aircraft cable core.  these are not quite as flexible as the standard spans, but work excellent, and you are not required, although I would adivise it anyway to use a steel cable backup.  3/8" to 1/2"  double eyed cable.  the same you would use to make a rig point.
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Timoteus Ruotsalainen

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Re: securing truss
« Reply #3 on: April 22, 2004, 09:37:07 am »

I don't do rigging as I'm in the starting points of my career in this biz (mainly audio).

The way I have seen rigging here (and have had a part in, although I was nervous to walk under the truss which we hung. That is NOT a good sign. Wasn't my idea and I wasn't qualified and wasn't responsible for it. ) is to attach a hand operated chain hoist to roof structures/mounting points in the roof. Then the chain is lowered and truss is constructed. the mounting to the chain from the motor is done with something that resembles this:

http://www.gweep.net/~prefect/pubs/iqp/img17.png
Copyright: http://www.gweep.net/~prefect/pubs/iqp/node51.html NOTE: this is just something I picked of the net.Not something that I or anyone I know have done.

after that the truss is lifted to about shoulder height for attaching lights. Then the truss is pulled all the way up. NO safety chains on lamps (nothing more than PAR64) or safety wires to roof structures.

So the proper way would be to rig like above and add a safety chain for individual fixtures (or is there a weight limit, like after 10kg must have safety chain) and a steel cable on both ends  that is secured to the points were motors are mounted.
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VDI

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Re: securing truss
« Reply #4 on: April 22, 2004, 11:15:07 am »

Ok, the picture you submitted is almost right.  the bottom choke is reversed.  the spanset should come up the outside of the bottom rail instead of, as pictured, the inside.  The safety steel should be run between the top and bottom rails and attached to the hook with a shackle where the spansets attach.  The spansets I mentioned earlier with the cable core are shorter, and can be rigged using the top rails.

Also, you asked about safety chains/cables.  Industry standard is usually one safety per instrument. An instrument/fixture can be a single unit, but a bar of 6 pars is also considered one instrument.  I however, like to be a bit more cautious, and use one safety for every clamp.  I don't care how small the fixture is, if it falls from above, it will hurt when it hits your head.

A point about rigging. (no pun intended)  If you are going to be hanging things, or rigging, over peoples heads, you should have some type of training.  Currently there is no certification for entertainment riggers. ESTA is working on a program to do just that, which will make it a bit easier to get insurance.  There are several publications available on rigging, and I believe in August there will be some kind of rigging workshop in Vegas.

If you choose to rig without insurance (not at all advised), make sure you rig properly.  if there is an accident, you're in a much better position if you've done everything by the numbers.
I would advise in the future  to hire an up-rigger through an insured local production company. (you can do the down yourself)  not cheap, but worth every cent.

Hope this helped.
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Brad Harris

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Re: securing truss
« Reply #5 on: April 22, 2004, 11:27:33 am »

I have 1 simple rule when rigging: If it can fall, it will.

Simply, everything requires a safety. The most common way of rigging truss to fly out is with a chain fall/motor attatched via spansets either on the truss, or up in the steel. Spansets generally are rated to ~2tonnes (~4000lbs). They are usually made from nylon, and can contain steel inside them. This isn't good enough in my opinion, and from most fire marshals. You want to put a 2nd all steel safety between the structural steel and the truss. You can pre rig the truss from the ground, and when you fly it out, just grab it there and continue in tieing if off either by looping it around the structural steel, or by a stinger.

This way you minimize the chance for a collapse to nearly non-existant if everything is up to spec within its limitations.
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Brad Harris

Timoteus Ruotsalainen

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Re: securing truss
« Reply #6 on: April 22, 2004, 11:40:52 am »

Very good and helpful advice.

I just want to make it clear that I am not a rigger. I don't rig stuff for a living or hobby. I have been part in some (only doing minor parts) riggings. However as I'm going into this business, I find it useful to have little bit of knowledge from all of the different areas. If I were to start rigging something on my own I would consult the real companies who do this for a living. I would also contact the proper authorities to check for local laws governing the issues associated with rigging.I would also get an insurance that covers the whole rigging process and the people involved.

But as I said earlier, I'm not a rigger. I'm not looking to be a rigger. I just want to have firm knowledge in all the areas of this biz. This way I can spot bad/dangerous riggings and maybe even stop them from happening.

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Timoteus Ruotsalainen
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Rob Timmerman

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Re: securing truss
« Reply #7 on: April 22, 2004, 12:12:46 pm »

Some random thoughts from my time working at a ropes course and my working with truss:

Nylon spansets are constructed almost identical to kernmantle rope: a woven sheath with a parallel strand core.  The sheath provides protection for the core, while the core provides the bulk of the strength.  But you can't see the core, so you don't know what kind of condition it is in on visual inspection.  To properly inspect a spanset, you need to feel the entire length of the sling for hard spots, soft spots, breaks, or anything else that seems abnormal.  Hard spots are where the internal strands fused together from heat.  There will be exactly one hard spot where the sling was formed.  This is normally under the tag.  Soft spots are possible frays, and breaks should be obvious.  Any of these abnormalities is enough to mark the spanset as no longer meeting its load rating, but it may still be possible to use these spansets as cable strain-reliefs.

As far as the all-steel backup goes, I'm not sure that that's a very good idea with aluminum truss.  We had a rule on the ropes course: "Steel to steel, aluminum to aluminum, webbing to anything (except aircraft cable)."  This is because the aluminum is enough softer than the steel that the steel could cut through it.  The only things allowed to make contact with aircraft cable were steel pulleys and steel carabiners.  I'd be happier with a steel-core spanset backup.

Nylon also deteriorates over time, especially outdoors.  Our standards were: rope replaced every 3 years, nylon webbing and harnesses every 4 years.  Harness and rope manufacturers recommend replacing nylon items within 10 years from date of manufacture.  If you use your spansets for outdoor festivals, where they sit in the sun all day, I'd replace the spansets sooner, probably when they start to fade.  


fwiw, Rob
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Alex_C

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Re: securing truss
« Reply #8 on: April 22, 2004, 05:54:56 pm »

Does anyone know of any good websites/pages which give a really basic introduction to rigging. I'm not a rigger, and leave that strictly to the professionals. One day I might be near one long enough to ask some questions, but until then I would still like to learn the basics - terminology, types of structure, safety, etc. - I work under these things every day, and yet know absolutely nothing about them!

Cheers people,

Alex

Edit:
Embarassed OK, so if i had looked at Timoteus' reply before posting, I would have seen http://www.gweep.net/~prefect/pubs/iqp/node51.html. Any more while I'm here?
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Craig Leerman

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spansets
« Reply #9 on: April 23, 2004, 09:12:52 am »

The older style all nylon spansets are not to be used anymore without a steel backup. This is because in a fire, the spanset will melt, and the truss or other stuff rigged in the air could fall on performers, patrons, or more likely, on Firefighters.

Our industry has shifted to what a lot of folks are calling "Steelsets" or "Steel Spansets". Basically, they look like an all nylon spanset, but have a steel core of aircraft cable with a nylon spanset outer shell/cover.  These are flexable enough to be used around truss and around beams for points.

Sapsis Rigging is a good place to start online for rigging. They also offer some training seminars as well as sell gear.

http://www.sapsis-rigging.com/

Fehr is another great rigging company.  Here is a link to their page  

http://www.stageriggingonline.com/

ATM is also a good place to look at, but they mainly focus on hanging audio stuff.

http://atmflyware.com/

Polar Focus is also another good rigging company, but they mainly service the sound end as well

http://www.polarfocus.com/

Craig
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I'm so old, when I was doing FOH for Tommy Dorsey, to balance out the horn section I would slide their chairs downstage and upstage to mix!


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