Stage & Lighting Truss

[ReverenceEng]

Hello,

I have a client that has a sub-contractor setting up a stage/lighting truss system that is freestanding. It's nothing complex and not that huge, but my client wanted to inquire as to the requirement for engineering. When they asked the sub for it, the sub apparently replied with something like "it's not required for freestanding stage trusses". I have attached a picture of a typical (small) truss system that is similar to my client's:

My client basically just wants me to research and respond to the sweeping generalization that "engineering is not required for stage trusses".

I am inclined to simply reply that whether or not a permit is required and whether or not the permitting agency will require engineering is up to the authority. However, I'd like to let them know if there is some sort of typical expectation with these things.

Also, I am coming up short with my research on references to these in building code and any other reference documents, but perhaps I am not using the most accurate search criteria.

1. Does anyone have any experience or expectation with these as to when a permit might be required and/or when a licensed professional might need to review and stamp off on it?
2. Does anyone know of any reference documents (code/ASCE) that outlines how these have to be designed / what loads, etc., which might help answer #1?

 

[JAE]

I'm sure it varies all over the place depending on the local jurisdiction and what ordinances, rules, inspection policies, etc. exist.

Best bet is to contact your local building permits department. There are also rules you will find regarding amusement rides, etc. Again - depends on the local laws.

Even if you find something in the IBC or other document, you still need to verify with the locals if it has been accepted, adopted or amended.

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[skeletron]

There's been a number of failures within the last decade or so. This one was pretty heavy in the news:

https://en.wikipedia.org/wiki/Radiohead_stage_collapse

Not trying to employ scare tactics here, rather, I would really take any light structure, with heavy load above crowds of people, with the risk of gusting, serious enough to engage an engineer.

 

[boo1]

check

https://www.structuremag.org/wp-content/uploads/2014/08/F-Stage_Rigging_Nolan_Mar_081.pdf

 

[jdgengineer]

It's my opinion that engineering should be completed for those lighting truss structures. Wind loading can be fairly significant forces on the structures. Ultimately, the enforcement of this is up to the local jurisdiction.

For relatively small structures (like in your photograph) we have designed the lighting truss as a moment frame. Typically the trusses are connected via bolts through an end plate at the end of each truss section. As this is how they connect the individual 10' pieces together, it seems reasonable to me to consider this as a moment connection as it hits the truss block at the joint. The corner truss blocks should have a load rating (and sometimes are used mid-span of the trusses).

Most of these lighting trusses only have diagonals on two sides and only have load ratings for load in this direction. For wind loading and other out of plane loads you will likely need to use engineering judgment. They do make trusses that have diagonals on all 4 sides. These should really be used for columns and any beams seeing significant out of plane loads.

I've never worked on anything larger than what you are showing and haven't completed engineering on a truss in several years. Someone else may be able to chime in who is more involved in the entertainment industry.