Line Array on Global Truss.

J

Jon Canaan

Freshman
Oct 17, 2011
3
0
0
Sacramento, CA
www.canaansoundandlight.com
Hi Everyone.

I want to hang 4 JBL VRX932LAP's on the VRX-AF array frame with front shackle and rear point shackle and I want to connect those shackles directly to the Global Truss Heavy Duty (full wrap cheeseborough) Clamp with Eye Bolt. The max weight rating of the clamp is 440 pounds. The non moving weight of the array is 220 pounds including the cabling. I would then do a round sling as a safety.

Is there any reason why shackles can't connect to other metal other than wire rope thimbles, or chain lift hooks? Everything I have seen on shackles is slings, wire rope and chain motor hooks. This would allow a rather solid mounting to the truss that will be lifted with heavy duty lifts.

Thoughts?
 
Re: Line Array on Global Truss.

Jon Canaan said:
Hi Everyone.

I want to hang 4 JBL VRX932LAP's on the VRX-AF array frame with front shackle and rear point shackle and I want to connect those shackles directly to the Global Truss Heavy Duty (full wrap cheeseborough) Clamp with Eye Bolt. The max weight rating of the clamp is 440 pounds. The non moving weight of the array is 220 pounds including the cabling. I would then do a round sling as a safety.

Is there any reason why shackles can't connect to other metal other than wire rope thimbles, or chain lift hooks? Everything I have seen on shackles is slings, wire rope and chain motor hooks. This would allow a rather solid mounting to the truss that will be lifted with heavy duty lifts.

Thoughts?
Click to expand...

John,

The primary reason that you see things done exclusively with rope-like systems is that they don't transfer moment couples to the remaining structure. Depending on the centroid of the array, and the certification of the WLL for the bolt (which is likely for a pure dead hang), your suggested arrangement does not account for the additional load vector(s) of the moment couple that is now transferred to the structure by the rigid connection.

http://en.wikipedia.org/wiki/Couple_(mechanics)
 
Re: Line Array on Global Truss.

Hi Phil,

Great response, and I have to admit, it took me a while to wrap my head around it. I think this would be true if I was hanging from only one of these eye bolt/clamp arrangements, but this would be front and back which would result in an evenly distributed dead hang configuration. Perhaps I can do without introducing moment couples above my stage.. Thanks Phil..
 
Re: Line Array on Global Truss.

Jon Canaan said:
Hi Phil,

Great response, and I have to admit, it took me a while to wrap my head around it. I think this would be true if I was hanging from only one of these eye bolt/clamp arrangements, but this would be front and back which would result in an evenly distributed dead hang configuration. Perhaps I can do without introducing moment couples above my stage.. Thanks Phil..
Click to expand...

Without knowing the centroid of the four boxes and the array flybar configuration, it is hard for me to agree with this statement. It might be a dead hang, it might not.

Also, even if the front and back points have identical vertical loads, the shear-stress loading placed on the bolts below the cheeseboroughs (or on the truss) as a consequence of any adverse load on the array (e.g. doing a chinup from the bottom box of the array) would probably overwhelm something, in shear, in an emergency situation.
 
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