Two Rigging Questions

[Tyler Herron]

I've got two questions in regards to rigging. This isn't a "how can I" thing. This is more of a theory and best practices question.

Almost all the rigging in my venue is attached to the beams with chain baskets, not wire rope. (see attached pic) The beams are not I-beams, they are more like two large pieces of angle iron welded. My question is, is the pointyness (technical term) of the beam the reason why they didn't use wire rope slings? Does it really matter if the basket is made out of rope, chain, or any other rigging material? I understand the diameter of the beam (or whatever you're wrapping the basket around for that matter) plays a big role in the strength of the basket. That's why there are entire chapters in books called D/d ratio.

My second question involves baskets as well. When constructing a basket, an example might be a 5ft basket around a beam in an arena, you have your working shackle attached to the eye of the 5ft sling, around the beam into a make shackle (terminology?) and then back into the working shackle. First of all, am I correct in that? That seems to be what I've been seeing out there on arena rigs. The question is, is there a purpose to the make shackle? Could the basket be constructed with just one shackle? Shackle->sling eye->around beam->back into working shackle? Eliminating the make shackle entirely..

Just some thoughts I'd like to get your opinions on.
-Tyler

 

[DuckJordan]

You'll see chain more often in installs (not moving) due to with a beam like that you'd want burlap between the steel and the beam (burlap looks bad on an install). As far as the working shackle. Yes you could do that, but the problem is when you have 75' of chain hanging down below you, and you are the one holding that chain from falling do you really want to take what is attached to your rope for hoisting apart to save a shackle here and there? its easier to keep it built and make the basket than make the whole point using the single shackle. Now that changes based upon how things are done for the rig. But in most venues the point and basket are per-assembled on the deck and the rigger pulls up by the working shackle so he can make the point easily. If you eliminate that shackle you don't have anything built anymore when you are in the air. More risk for less money...

Now if you pre build all your baskets in the air then bring the chain up to it I could see that working but again. Most of the time everything is pre rigged on the ground then hoisted up.

 

[soundman]

My second question involves baskets as well. When constructing a basket, an example might be a 5ft basket around a beam in an arena, you have your working shackle attached to the eye of the 5ft sling, around the beam into a make shackle (terminology?) and then back into the working shackle. First of all, am I correct in that? That seems to be what I've been seeing out there on arena rigs. The question is, is there a purpose to the make shackle? Could the basket be constructed with just one shackle? Shackle->sling eye->around beam->back into working shackle? Eliminating the make shackle entirely..

Just some thoughts I'd like to get your opinions on.
-Tyler

The local from where I grew up has a some great info on basket construction. What Duck said is pretty much true. When you are 75'+ after pulling up 80 pounds of rigging you want to make it easier on yourself. With a working shackle you only have two things that can fall. The pin and the bell of one shackle. If you don't have a working shackle you end up with a lot more parts that could fall.

 

[derekleffew]

... around the beam into a make shackle (terminology?) ...

I've never heard the "extra" shackle called a "make shackle," but have heard it referred to as a "rock&roll shackle." Primarily saves time, but also easier and safer.

As for chain vs. wire rope, there's considerable debate about whether proof-coil chain is acceptable for overhead lifting/suspension. See http://www.controlbooth.com/threads/a-question-about-stac-chain.31059/ .

 

[Tyler Herron]

That makes total sense! I didn't think about that (that's why I'm not an arena rigger, lol).

I figured the chain thing might be because of the install, but I guess I was thinking chain wasn't really meant to have forces at an angle like that. The link resting on the edges of the beam are basically being pulled at a 90 deg angle, which I'm sure definitely lowers the capacity of the chain. Which brings up another curious question: which is more resistant to that type of force? Chain or wire rope? Does a forged piece of metal withstand the force of a 90 deg bend more than wire rope? I imagine the diameter of the bend again is important.

I'm starting to just think out loud now I just ordered Entertainment Rigging by Donovan so I'll be answering these questions myself soon (hopefully)!

 

[Footer]

Personally, for any permant install I would rather see a beam clamp to in vs the basket. Nothing against the basket, but a clamp is much cleaner and easier to give a true rating to what is hanging from it.

 

[MPowers]

For a permanent install, slings or baskets around steel beams are poor rigging practice regardless of whether they are of chain or cable. The 90d bend compromises either one. For a permanent installation of a non-moving line, the D:d ratio should be at least 5:1 (think about the bend in a cable as it is installed in a thimble eye). For chain the minimum bend radius should be about the same as one link of the chain (think a 1/4" chain around a pipe batten, roughly 1" radius).

Good rigging practice for permanent installations is to use beam clamps.

 

[Tyler Herron]

Interesting and great information guys! Thanks! I would assume the chain baskets are still secure even though they aren't recommended. I don't need to go out and buy 200 beam clamps and replace everything in my venue do I? (read: hire a professional to buy 200 beam clamps and replace everything)

 

[FatherMurphy]

Although replacing all the baskets with beam clamps would clean things up a bit, I'd suggest first getting a professional rigger or structural engineer to take a close look at what's there, and run the numbers. Although the bends derate the chain, if the strength is high enough to start with, then you might still be fine as-is. More likely, though, they won't be able to sufficiently identify the chain to get an accurate strength, and will either have to low-ball it, pull-test some samples, or declare it all unknowable. Although it'll be more expensive in the long run to inspect and replace, instead of just replace, if the inspection comes back negative, then you have an outside opinion to help your argument for the expense of making the changes.

As for the 'pointy' orientation of the beams, a corner is a corner, doesn't really matter to the basket if the beam is 'square' or 'diamond', it's still a 90d bend.

As for shackle nomenclature, around here we refer to the 'master' and 'free' shackles in arena rigging baskets.

 

[cmckeeman]

If i am in a ballroom, then i just use one shackle for my basket, but out on beams you tie into the working shackle and that hols the weight now all you have to do is unscrew the free shackle pin and pop the eye in. . As for the chain, you are applying quite a bit of side pressure to the chains, and I'll admit I'm not 100% sure it's wrong or unsafe, but i am 100% sure a beam clamp would be just as good if not better.

also has anyone experimented with putting the free shackle in the eye then you only have the bell and pin to deal with instead of an eye, pin and bell with only two hands?

 

[FatherMurphy]

has anyone experimented with putting the free shackle in the eye then you only have the bell and pin to deal with instead of an eye, pin and bell with only two hands?

It's more annoying that way, harder to line up the pin into the master shackle with a rope and the other end of the basket steel already in it. With the bell of the free shackle in the bell of the master shackle, you only have to get the free shackle's pin slid back far enough get the basket steel's eye onto the pin, then you can slide the pin back in quickly and easily, plus both the free shackle and steel eye are free to move about for alignment, whereas the master shackle is held tight and can't flex. I don't really worry about the free shackle's bell falling (low probability not-worry, not unconcerned not-worry), as the ends are usually big enough around that popping out is unlikely. The size of the ends also means that there could be clearance/fit issues if you didn't make up shackles bell to bell.