# Calculating Load Limits?



## Sony (Sep 21, 2010)

So I have been given a load limit of 65 Pounds per Linear Foot for a grid I will be designing on later this year. Just wondering is there any way to calculate the Uniformly Distributed Load Limit and Point Load Limits from this number? The Grid is a 6ft square grid supported by 1/2" steel rods at every junction but not secured to the walls at all. So there is 6ft between each support, and the grid is made out of standard 1.25" Schedule 40 pipe.

So thats the question, using this information is there any way calculate my UDLL and PLL for say if I wanted to hang a piece of scenery off of the grid or maybe some truss?


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## Footer (Sep 21, 2010)

Yup, the formula do exist to do that. However, you can not go from PLF to a point load without knowing the type of material you are going to be hanging from, what each point can handle, and how much deflection the material and your sanity can handle. The point load also changes depending on where you are, but usually you figure it for the worse case scenario. Pick up this book... Amazon.com: Structural Design for the Stage (9780240803548): Alys Holden, Ben Sammler: Books . It will give you all the formulas, tables, and everything else you could possibly ask for. It will give you the piece of mind to know EXACTLY how much you can load any grid/truss/deck.


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## kendal69 (Sep 22, 2010)

Get this software:
Rigging Books, Cards and Programs

Designed by the late Harry Donovan arguable the foremost master of rigging. I was honored to take one of his last classes.


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## Footer (Sep 22, 2010)

kendal69 said:


> Get this software:
> Rigging Books, Cards and Programs
> 
> Designed by the late Harry Donovan arguable the foremost master of rigging. I was honored to take one of his last classes.



That software is great, but is a bit overkill for this. Before you use the software, you should know what the software is actually doing. If you can't do it on paper, you don't know why the software is doing what it is doing. Never blindly trust a computer's math. Its a tool, its not a solution to find an answer that you can't find yourself... at least in this case. People that are building spaceships and that kind of thing.... computer away!


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## church (Nov 29, 2010)

You ask a good question but reading a book and using a software program on their own do not provide the required knowledge and skill to perform these calculations and then rely on the result when an error can have fatal consequences. Get someone who is qualified to do the calculations and explain how it is done.


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## museav (Nov 29, 2010)

church said:


> You ask a good question but reading a book and using a software program on their own do not provide the required knowledge and skill to perform these calculations and then rely on the result when an error can have fatal consequences. Get someone who is qualified to do the calculations and explain how it is done.


+1. I would guess that the final grid design would have to be signed and stamped by a registered Structural Engineer so they're probably going to run calcs anyways. I'd also like to reiterate Footer's point that no matter what you do for the grid itself, the potential allowable loads for the overall grid system are also dependent on the attachment of the grid to the building structure. This bit me once with a speaker install when it turned out that the massive concrete beams we intended to hang from were already at the maximum design load and we couldn't place any additional load on them, thus having to double or even triple the span to get to beams we could use which obviously affected the structure required.


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## Sony (Nov 29, 2010)

This thread is old and a moot thread anyways, we got the specs we needed about 2 days after the final post in this thread. I was only asking because the structural engineer was being fussy and wasn't giving us the numbers we needed.


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## MPowers (Nov 30, 2010)

Sony said:


> So I have been given a load limit of 65 Pounds per Linear Foot for a grid ........... The Grid is a 6ft square grid supported by 1/2" steel rods at every junction but not secured to the walls at all. ......... the grid is made out of standard 1.25" Schedule 40 pipe.



Got a couple of questions/points here. 

First, standard loading per linear foot recommended by ESTA, and every rigging company and installer that I know of is 30 pounds per linear foot.

Second: A pipe grid that is not secured to the side walls and hung from rod is far against all good rigging practice unless substantial cross bracing is incorporated into the design.

Third: "Standard" pipe used in entertainment industry for hanging lights is 1 1/2" not 1 1/4". 

Forth: 1 1/4" pipe is not rated to support 65 pounds per foot on a 6'-0" span.

If this pipe grid design is built and installed as you describe, there will be some serious safety concerns and I for one, would refuse to work on or under it.

Oh, by the way, I've been designing and installing, rigging and pipe grids for over 30 years. I've installed over 100 pipe grids in schools TV studios, black boxes and etc. so i do have some slight knowledge of the subject.

Here is an excerpt from InterAmerica one of the Nations' premier pipe grid and tension grid manufacturers and installers.
=======================
Our standard grid specification is based on a linear foot live load of 30 pounds per foot. Special considerations are required for heavier loads, especially point loads. Examples of a heavy point load might be a 250+ pound speaker or TV monitor 
The standard pipe grid consists of 1-1/2â€￾ schedule 40 steel pipe battens crossing at right angles. The upper level of battens run in one direction and is suspended from the building structure. The lower level of battens is clamped perpendicular to the upper pipe battens. Our cross clamps are the heaviest duty found in the industry. Our clamps lock the crossing pipes together at a perfect 90 degrees.
For lateral stability, at least two ends of the pipe grid should be attached to walls. This attachment can be a support shelf running the full width of the grid along each wall, or individual wall flange brackets.
==============================


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## Sony (Nov 30, 2010)

Okay look... I'm really not happy that somebody decided to bring this thread back up. The grid is safe, and since this thread opened there have been serious modifications to make it safer, including cross bracing and beefier supports, all done by the engineers and installers who designed the grid. There is even talk about replacing all the pipe with 1.5" schedule 40 and bolting it to the walls but 1.25" schedule 40 will have to do for now. If you had read my previous post you would have realized the situation has majorly changed since I started this thread hence this thread is entirely moot and I have the numbers I need, so please let it be...I really don't want to have to ask to have this thread deleted.


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## erosing (Nov 30, 2010)

Sony said:


> Okay look... I'm really not happy that somebody decided to bring this thread back up. The grid is safe, and since this thread opened there have been serious modifications to make it safer, including cross bracing and beefier supports, all done by the engineers and installers who designed the grid. There is even talk about replacing all the pipe with 1.5" schedule 40 and bolting it to the walls but 1.25" schedule 40 will have to do for now. If you had read my previous post you would have realized the situation has majorly changed since I started this thread hence this thread is entirely moot and I have the numbers I need, so please let it be...I really don't want to have to ask to have this thread deleted.


 
MPowers point(s), I believe are very relevant to the future for those that may join in a similar situation. While they seemingly reference you, I would assume they are to note the corrections that have otherwise not been noted already. Not to embarrass you, but to help others.


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