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Author Topic: Question for the rigging experts.  (Read 31793 times)

Jonathan Johnson

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Re: Question for the rigging experts.
« Reply #60 on: April 04, 2012, 02:19:06 pm »

With all due respect to the original poster, who IS very interested in doing things the right way, I'd like to address the issue somewhat academically.

There is a right way to do anything. The right way is rarely the easy way, and even more rarely the inexpensive way.

In the case of overhead rigging, the primary concern is always safety. Secondary is liability. For such an install, if there is a failure of any type, the question "whose fault was it?" will ALWAYS be asked (at least as until lawyers and insurance companies become extinct). Such failures may include other things such as structural failure or property damage, not necessarily personal injury or loss of life.

Consider structural failure. The worst snowstorm in decades rolls through town, and your roof collapses in the middle of the night. No one was injured. Your insurance company will investigate, and find there was a load added to the roof structure. Immediately they will question if this was a contributing factor. If the load was engineered, it is less likely the investigators will pin the blame on that load. If they do, the liability falls upon the engineer. If the load was NOT engineered, it falls under much tighter scrutiny and is more likely to be blamed, and you will be liable. You may be denied insurance coverage.

Someone mentioned that speaker manufacturers publish rigging guidelines. I'd like to point out that these rigging guidelines cover everything from the hang point downward; they do not and cannot consider anything above the hang point. Even with these pre-engineered rigging systems, you still need an engineer to design or approve the method of attaching the system to the existing structure.

As for getting your rigging from a hardware store: if it doesn't have a load rating, it's simply not acceptable to install no matter how strong it looks. If it does have a load rating, you MUST retain the labeling as documentation of the rating. Further, realize that the load ratings on this hardware are single-directional yet do NOT specify what direction that is (usually linear). You would need to contact the manufacturer to get detailed information. Also, note that nearly all hardware store "rigging" hardware is labeled "NOT FOR OVERHEAD LIFTING." That means it's unacceptable for hanging stuff over people's heads. While the ratings may be the same as professional rigging, that label means the manufacturer claims no suitability of purpose and accepts no liability in the event the hardware fails when used overhead.
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Charlie Zureki

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Re: Question for the rigging experts.
« Reply #61 on: April 04, 2012, 04:04:57 pm »

With all due respect to the original poster, who IS very interested in doing things the right way, I'd like to address the issue somewhat academically.

There is a right way to do anything. The right way is rarely the easy way, and even more rarely the inexpensive way.

In the case of overhead rigging, the primary concern is always safety. Secondary is liability.



  Hello,

  I suppose that you hadn't read the entire thread...

 1.)  In the first post, Void had his structural guy look at the gear's load, the structure, truss, etc...,  and approved the hang.

 2.)  Void never posted that he bought his rigging components from a hardware store... where did you get that info?  In a follow up post he clearly stated that he purchase the hardware from a company that supplies rigging gear and rated hardware.

 3.)  Where did you get the idea that "all hardware store "rigging hardware" is labled "Not for overhead lifting" ?   Sure...there are those cheap aluminum caribiners that can be found at most hardware stores that are only rated to 60lbs or up to 160lbs (most often these are used to clip keys to a belt)
...and most often they clearly state that they are rated for 60lbs (or whatever) and "not for climbing".   But, you're also saying that nuts and bolts cannot be used for overhead lifting?  Even the higher grade nuts & bolts like grade 5, 6, 7 or 8 ?   Or rated hardware store clips, quicklinks, or even wire rope, thimbles and cable clamps ?   

  Nonsense... when one chooses hardware, it is probably a wise choice to buy all of the hardware from an industrial supply house or company that specializes in rigging gear and hardware, but, most of the hardware found in the typical hardware stores and home centers have ratings. It's  either on the individual item or, on the spool or bulk package.  Whether it fits your rigging criteria, or an approved criteria,  is another story...

  Hammer
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Jonathan Johnson

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Re: Question for the rigging experts.
« Reply #62 on: April 05, 2012, 01:27:36 am »

  Hello,

  I suppose that you hadn't read the entire thread...

 1.)  In the first post, Void had his structural guy look at the gear's load, the structure, truss, etc...,  and approved the hang.

My post wasn't directed toward Void, it was directed to the layman reading this who will think it's the answer to a problem (which most of the people commenting here have taken great pains to point out that it is not). I simply wished to highlight some things that a casual reader should note.

Quote

 2.)  Void never posted that he bought his rigging components from a hardware store... where did you get that info?  In a follow up post he clearly stated that he purchase the hardware from a company that supplies rigging gear and rated hardware.

Yup, I saw that. But the casual reader may look at the pictures and think that they look just like the ones on the hardware store hook.

Quote
3.)  Where did you get the idea that "all hardware store "rigging hardware" is labled "Not for overhead lifting" ?   Sure...there are those cheap aluminum caribiners that can be found at most hardware stores that are only rated to 60lbs or up to 160lbs (most often these are used to clip keys to a belt)
...and most often they clearly state that they are rated for 60lbs (or whatever) and "not for climbing".   But, you're also saying that nuts and bolts cannot be used for overhead lifting?  Even the higher grade nuts & bolts like grade 5, 6, 7 or 8 ?   Or rated hardware store clips, quicklinks, or even wire rope, thimbles and cable clamps ?   

  Nonsense... when one chooses hardware, it is probably a wise choice to buy all of the hardware from an industrial supply house or company that specializes in rigging gear and hardware, but, most of the hardware found in the typical hardware stores and home centers have ratings. It's  either on the individual item or, on the spool or bulk package.  Whether it fits your rigging criteria, or an approved criteria,  is another story...

  Hammer

No, it's not all labeled "not for overhead lifting." (I said nearly all...) But most of the hooks, links, chain, and cable that I've seen actually are labeled "not for overhead lifting," right next to the force rating.

Yes, most big-box hardware has ratings. BUT it's very atypical for those ratings to specify how the force is applied (linear? shear? torsional? angular? multiple angles?), so the layman isn't going to be able to make an educated choice without an engineer's assistance.

If the hardware store has exactly what your engineer specifies, by all means, go ahead and use it.
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Mike Fariss

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Re: Question for the rigging experts.
« Reply #63 on: April 12, 2012, 02:07:31 am »

A few points regarding chain.  It should be pulled in a straight line only.  It is OK to be used in other than straight vertical, the chain just has to be in a straight line.  The links should never be side loaded as this exerts forces that it was not designed for.  This can pull apart the welds.  Cutting the chain and using 2 links will fix this as the OP said they will do.

I do not use quick links but believe that the same rule applies in that it should be used inline only and not side loaded as someone else suggested. 

I do see an issue with how the eye bolt is installed.  It needs to be tight to the shoulder.  The photo shows that there are nuts and a few inches of threads between the structure and the shoulder pad.  The eye bolt should be cut to size and the double nuts should be above the structural steel.  Currently the eye bolt shaft can be bent loosing strength.  An earthquake or other event will put all kinds of side loading on the bolt that it can not handle.   Just because you are not in Sothern California dose not mean that anyone should take this for granted.

Side loading the eye bolt is OK as long as you derate its capacity approitly.  Pulling at 45 deg off of a straight line you only get 30% of the eye bolts rating.  I looks like it is a 3/8 bolt so 2 VRX should be within tolerance, but check it.

Here is warning information on proper use and installation for eye bolts:

http://www.thecrosbygroup.com/html/en-US/pdf/pgs/180_181.pdf
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Robert "VOiD" Caprio

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Re: Question for the rigging experts.
« Reply #64 on: April 12, 2012, 10:20:24 pm »

Well everyone,  opening night has come and gone.  Things went very well, the club owners couldn't be happier.  The music rocked,the drinks flowed... and nothing fell from the truss :)

I fixed the chain so it's now two pieces straight out from the eyebolt.  I'll post another pic of the setup ASAP. 

Thanks for all the help and advice.
« Last Edit: April 12, 2012, 10:22:37 pm by Robert "VOiD" Caprio »
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GenePink

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Re: Question for the rigging experts.
« Reply #65 on: April 17, 2012, 07:14:38 am »

I have enjoyed these seven pages of posts, the bantering, arguing, posturing, etc. I see nothing has changed around here, that is kind of comforting, in a twisted way.

What does surprise me is that nobody brought up what I see as the weakest point in this hang,  refer to the OP's second picture, the close-up of the long threaded eyebolt that goes between the two pieces of angle-iron of the existing roof truss.

The nuts tightened from above and below will deform the washers into a bit of a wedge shape, trying to wedge in between the angles causing them to spread apart.  They are not very rigid at this point, it is a good distance to the nearest point on either side where they are tied together by the diagonal roundstock.

I would feel more comfortable seeing some sort of large 1/4" thick plate on the top that extends out past the outer flanges of the angle-iron, spreading the load out over the entire top surface of the truss, and removing the force that is tending to twist the angle. Angle-iron is very flimsy when in comes to torsional forces, with the load concentrated on the top inner edges, and the wedge washer trying to spread the bottoms apart.

Hanging from this sort of roof truss has to be common enough where there is a simple off-the-shelf rigging product made for this.

Gene

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Charlie Zureki

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Re: Question for the rigging experts.
« Reply #66 on: April 17, 2012, 09:52:35 am »


What does surprise me is that nobody brought up what I see as the weakest point in this hang,  refer to the OP's second picture, the close-up of the long threaded eyebolt that goes between the two pieces of angle-iron of the existing roof truss.

The nuts tightened from above and below will deform the washers into a bit of a wedge shape, trying to wedge in between the angles causing them to spread apart.

I would feel more comfortable seeing some sort of large 1/4" thick plate on the top that extends out past the outer flanges of the angle-iron, spreading the load out over the entire top surface of the truss, and removing the force that is tending to twist the angle. Angle-iron is very flimsy when in comes to torsional forces, with the load concentrated on the top inner edges, and the wedge washer trying to spread the bottoms apart.

Gene


  Hello Gene,

    I suppose that you missed Void's post stating that he used the flat, square Unistrut washers on the top side of the truss.  These washers are rated for at least 1600 lbs.

    Cheers,
    Hammer
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Re: Question for the rigging experts.
« Reply #66 on: April 17, 2012, 09:52:35 am »


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