Rigging - Arena

[Brixtonbanner]

I am an arena rigger I suspend electric chain hoists from arena roof beams for shows, events, gigs etc.
I saw this thread about D:d ratios
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PascalFleischman (Structural)
16 Jan 08 15:46
After exhaustive searching, I've found it.

FYI:

When D/d < 6:

%E = 1 - (1/(2*(SQRT (D/d))))

When D/d >= 6:

%E = 1 - [.76 / ((D/d)^.73)]
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my concern is all the info I can find regarding D ratios and their effect on sling efficiency seem, to me, to refer to passing the steel around a shackle or pulley/sheave. i.e. the steel goes through 180degrees at the bearing point.
I wrap , for example a 10' 10mm. Steel wire rope around a beam that's perhaps 10" wide and 10" deep. so the steel goes round a series of 90degree bends.
I use burlap/sacking (folded a lot) to pad out these bends to increase the d:d but it is not by much.
After that preamble my question is this
Does the above formula work in my application?
If not and anyone could point me in the direction to find a workable formula I would be very grateful

 

[MikeHalloran]

I don't think the formula is going to work for burlap cushions.

How about dumping the burlap and welding some wire rope thimbles across some short angles? You can lash the angles to the beam corners, and ty-rap the wire rope into the thimbles. That will at least have you working with a known radius.




Mike Halloran
Pembroke Pines, FL, USA

 

[Brixtonbanner]

Mike
Your idea would make sense in an istallation world but in a touring situation it would not.

Different town every day, different beam sizes, different crew.
Load into venue at 7:00 and have to be done by 11:00
In one venue your 85 one tonne points are mostly dead hangs because there is a mother grid, in the next venue they are virtually all hanging off 2 or 3 way bridles apart from the ones in the middle of the hall which are under the arenas ice hockey scoreboard so they have to be on H bridles. etc.

all of the above factors mean there isn't time or truckspace to make or transport anything more sophisticated than burlap

 

[cloa]

http://www.petrospec-technologies.com/Herkommer/knots/FM5-125.pdf

Army manual on rigging- maybe that has something useful for you.

 

[Brixtonbanner]

Thanks I'll have a read

 

[EdStainless]

You need to look for something tougher than burlap for your corner padding. There are woven synthetic fiber mats that would be more cut resistant.
There is info that I can't find right now that is from the mining industry. Preventing cutting by rocks is a big deal.
There is also padding that is used on pipelines before the back fill in order to prevent damage.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[PersonalProfile]

Suggest you review a local equivalent to this (p5 in particular):

http://www.deir.qld.gov.au/workplace/resources/pdfs/guide-for-doggers.pdf

There may be other forums on this site which would yeild more responses than this one.

Regards,
Lyle

 

[Brixtonbanner]

Thank you for those interesting responses
But back to my core question
The formula
%E = 1 - (1/(2*(SQRT (D/d))))

When D/d >= 6:

%E = 1 - [.76 / ((D/d)^.73)]

Is this for a 180 degree bend or would it be equally correct on a 90 degree bend?

 

[cloa]

This is an appropriate or helpful forum for your question- don't know if there is one in Eng-tip.com How about you try

http://www.lifting-world.co.uk/forums/viewforum.php?f=95&sid=52f2a0064202e5328eb4caa844155d71

 

[cloa]

http://www.eng-tips.com/threadminder.cfm?pid=406

Gear and pulley engineering or maybe Mechanical Engineering other topics is about as close as it gets Eng-tips.com

 

[Brixtonbanner]

thanks I'll have a look