using too many Chainfalls ?
- Thread starterDagger
- Start date
No way to know what anything you saw was rated for, size of the truss, or such, but assuming all things are equal and the truss is loaded uniformly, 3-point lifts consolidate much of the load on the center point while the outer two points get a fraction of the load. Whereas loads are much closer to balanced in a 4-point hang. Note, that generally speaking, a 3-point hang consolidates more of the load on the center point, 62%, than any other possible configuration. Your outer chainfalls are doing almost none of the work in comparison.
See below reference image.
See below reference image.
@Dagger Were there adequately rated points directly above where you wanted them?
Toodleo!
Ron Hebbard
Yes there is a adequately rated beam on top of where I would put the 3 chainfalls. ( I believe the style of ceiling is called J Truss - correct me if I am wrong - see image 1)
The truss is 40' length and 12 lekos @ 20 lbs each = 240 lbs + U- Ground and DMX- let's say 50 lbs of cable ( way overestimated cable weight.)
Total load 290 lbs.
IF I am reading the christie lites truss chart correctly? Image 2
Based on the christie lites truss chart quarter point load at 40 ' is 3x100 (300lbs)
So 3 chainfalls are within the allowable load?? ( not considering safety factor 1:5)
Help appreciated. Thanks.
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Asking for specific rigging advice over the internet is not a good idea. If you have concerns about what you are doing, work with a local professional to alleviate them.
You are not reading that chart correctly. That is not describing the number of hang points from supporting structure. The Maximum Allowable Point Load is describing that for a 40' span supported at the ends, with 3 evenly separated point loads, you can hang 100lbs on each point from the truss, located at quarter points. This is as opposed to a Uniform Load, which 12 evenly spaced fixtures would be more representative of.
Nothing in that chart represents the total load applied to the actual lift points the truss is suspended from, nor does it represent a 40' stick with 3 mid-span lift points. Think of that chart as representing a ground-supported truss span, with a tower on either end that the truss is supported from.
Unless you know for a fact that this truss matches the Christie Lights 12" Type A, you also cannot assume this chart generally represents all other forms of 12" truss. Each manufacturer and product has its own ratings and instructions that should be referenced for a particular product.
I would also not look at any particular structure supporting a roof and other equipment as obviously adequate for additional structural loads. You do not know what the structure is capable of, nor do you know what the other loads are on the roof, including possible rain and snow loads.
Nothing in that chart represents the total load applied to the actual lift points the truss is suspended from, nor does it represent a 40' stick with 3 mid-span lift points. Think of that chart as representing a ground-supported truss span, with a tower on either end that the truss is supported from.
Unless you know for a fact that this truss matches the Christie Lights 12" Type A, you also cannot assume this chart generally represents all other forms of 12" truss. Each manufacturer and product has its own ratings and instructions that should be referenced for a particular product.
I would also not look at any particular structure supporting a roof and other equipment as obviously adequate for additional structural loads. You do not know what the structure is capable of, nor do you know what the other loads are on the roof, including possible rain and snow loads.
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RickR
Well-Known Member
This is why Structural Engineers get work in the entertainment industry!
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