Is it safe ?

SteveB

Well-Known Member
A new facility with a large music rehearsal room that has a minimal electrics rig, 4 pipes 32' long, schedule 40 1.9 OD under an ETC raceway, the electrics span the short side (SL/SR) of the room. The 4 electrics are rigged to a Kindorf channel steel system that spans some of the US/DS length of the room, 5 - 3/8" threaded rods as hanger from each electric to Kindorf. Length of Kindorf structure is approx 45 ft.

The Kindorf is itself installed with each US/DS section using threaded rod to beam clamps onto steel above the finished ceiling. There a total of 5 rods per Kindorf length, 25 total threaded rod support points for the entire system. There is no lateral support to side walls of the electrics, they just gravity hang from the rod/Kindorf structure.

The lighting design from the early stages called for 30 S4 Pars as overhead washes, 6-8 per electric and that's what's installed. There are 6 circuits only per raceway (with add'l circuits on the side walls).

The only drawing we have, a blurry PDF, has the stamp of a structural engineer, but the drawing is NOT what was installed, as they realized during construction that the electrics were intended to rod hang direct from the lateral steel beams and could not, as the beams did not line up where the electrics needed to be, thus the rigging installer did the Kindorf structure. We do not have an as-built drawing, so no idea as to weight capacity nor information as to any sign off by an engineer.

The Dept. of Theater desires to strip the 30 S4 Pars and hang an LED rig for an event, approx. 20-23 Lustre II's on each electric . We have concerns about the weight capacity of the steel rod/Kindorf/beam clamp. We can calculate the 20 lbs per fixture with clamp, but are uncertain of the load limit of the grid.

We have a call out to the rigging installer, a nationally well known rigging installation company, as to 1) Are there as-built drawing ?, 2) Did a structural engineer sign off ?, 3) Do they have any thoughts on the load capacity of the rig ?.

But I thought I would run this past my colleagues at CB as to their thoughts.
 

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I'm NOT a structural engineer but the parts ratings far exceed the load and any likely future load.

AFAIR cheap 3/8" rod is rated to 1800+ lbs WWL and I often spec battens to 20lbs per foot max load. That's a S4 every foot! 750 + batten and distro maybe 1000lbs? So each drop can do nearly twice an entire run. More if they used better rods. I'd have to dig out the strut specs, but since I see double strut, it seems similarly capable.

Sway is limited by the drop length relative to the spacing. You're not in earthquake country are you?

What do you think is the weakest link?
 
I'm NOT a structural engineer but the parts ratings far exceed the load and any likely future load.

AFAIR cheap 3/8" rod is rated to 1800+ lbs WWL and I often spec battens to 20lbs per foot max load. That's a S4 every foot! 750 + batten and distro maybe 1000lbs? So each drop can do nearly twice an entire run. More if they used better rods. I'd have to dig out the strut specs, but since I see double strut, it seems similarly capable.

Sway is limited by the drop length relative to the spacing. You're not in earthquake country are you?

What do you think is the weakest link?

Weakest link I suspect is the threaded rod, one rating I saw was 600 lbs., another for load-rated was 2,400 lbs, so all over the place. Plus I've no idea as to the capacity given span of roughly 8-10 ft between rod sections from Kindorf to roof.

https://www.engineeringtoolbox.com/loads-hanging-rods-d_1341.html

The ability of the entire structure to sway also concerns me.

And while not in a designated earthquake area, there was an earthquake back in 2010 or so, which resulted in new NYC codes as well as a complete building re-design to meet those more stringent city codes, go figure.
 
The Lack of lateral bracing is astounding.

Without inspecting the attachments to structure it would be impossible to judge the rating. The suspension scheme, number of roads per pipe run, gauge of Strut and Rod, would appear to be sufficient to handle a 20#/linear foot rating. All of that could be for nothing if it's connected to TGI joists incorrectly, or if it's installed on overloaded Open Web Trusses, or if any of the hardware used was not actually properly rated.

Your contacting the original company is probably best. 'Field Engineering' happens when issues crop up but if the Job called for and engineering stamp in the first place any redesign of the support structure would be required to be run through the engineering process again. Someone, with the Physical plant of the school or the GC in charge of the construction does have an O&M manual along with a full set of drawings and engineering data.
 

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