# Strength of Wood and Metal



## erosing

Full Disclosure: This is a question that I stemmed off of from writing an academic paper.

I was looking through my books and unless I missed it somewhere I could not find any references to the strength of plywood, sheet metals, metal tubing, or wood and metal in general when concerned with platforming. I am now wondering if I missed it somewhere or if it simply does not exist. 

For example purposes only:

Would a platform, with proper framing, covered in 1" ply have twice the strength of one covered in 1/2" ply? 

Does a 2" metal square tubed frame have twice the strength of a frame with 1" tubing?

What about solid vs. tubed metal framing?

Does a 2x4 have half the strength of a 4x4?

I'm still searching the rest of my books and I have not made my way to the internet yet, but I'm curious if such information exists somewhere. Bonus points if it's somewhere in a book I can add to my collection.


These are the books of gone through so far and as far as I've seen none have gone into the strength of materials.

Stagecraft 1: A Complete Guide to Backstage Work – William H. Lord
The Stagecraft Handbook – Daniel Ionazzi
The Backstage Handbook – Paul Carter
Stage Scenery and Lighting – Samuel Selden
The Health & Safety Guide for Film, TV & Theater – Monona Rossol
Stage Crafts – Cris Hoggett
Scene Design and Stage Lighting – W. Oren Parker and R. Craig Wolf


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## FatherMurphy

I think the information you're looking for is more likely to be found in a structural engineering text than a stagecraft book, especially the relative strengths of materials. Tables do exist, but you also have to know specifically what sort of load you're asking about. Most load tables you'll find for, say, rock and roll truss, is for a horizontal beam flexibly supported at both ends. Other tables exist for rigid end supports, one rigid and one flexible, cantilever, vertical, torsion, etc., etc., etc. Then you have to consider what else is attached to the item, and how it's attached. A platform framed with 1x6, with spreaders screwed every 12", will load differently than one with 2x4s nailed every 24". Housing construction books will have some charts for standard construction techniques that may cross over to theater, but they still won't give you more than a general idea of differences, plus they're looking at floors built as a single unit, not modular platforms.

Most manufacturers will have charts for their products, so you might search for those. Texts such as 'Machinery Handbook' will have some strengths of metals info, and load charts for steel shapes aren't hard to find. For regular lumber, you also have to consider each board separately - a knot in a highly stressed location can be a bad, bad thing. Orientation is also important - you asked about 2x4 vs 4x4... is the 2x4 flat or on edge?


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## Dover

A simple question without a simple answer. From an engineering stand point most of your questions can not be answered, because it depends more on how you build it and not on what you use. A platform carries the load as a system not as individual components. Knowing the yield strength of 3/4 ply and 8' 2x4s and adding them up will not give you the same result as testing the platform as a whole. As for the question of solid vs. tubing I can not think of an application in theatrical platforming where tubing would not be stronger by weight.

If you wanted to pursue this further I would recommend an structural engineering text, as I do not think that any stage craft book will get that deep in to the engineering of platforms. Or if this is a collage paper go down to the engineering department and they might be able to assist you in analyzing various materials and designs. 

Dover


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## mjw56

Steel is stronger than aluminum and aluminum is stronger than wood (for objects with the same cross section) the strength of steel wood and aluminum, along with everything else in the world, is dependent on the grade or species. wood strength is different for almost every species group and then different grades of each species group have different strength. 

if u already have a slight bit of structural knowledge there are a few books which would allow u to become dangerous. on that note this is for education only. don't go off designing any structure until u have a P.E. liscence and professional liability insurance to cover ur [email protected]#

for wood u want to get the NDS from the American Forest and Paper Association. it lists all the formulas, load factors and strengths of materials contains deifferent sections for sawn lumber, streesed skin panels, glulams, etc. and is confusing enough to scare u a way from trying to design.

for steel AISC Steel Manual. lists all the same stuff. i cant attest to its level of confusingness though as i dont own one.

im not sure if there is a book for aluminum


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## Footer

There is one book you want. Amazon.com: Structural Design for the Stage (9780240803548): Alys Holden, Ben Sammler: Books

If you are an anti-Yale person, you might not like this book... but it is the best book out there for any technical director. 

I have designed some pretty insane systems using these book. 

It is the end all be all book when it comes to figure out loads onstage. It is my most used book. It never leaves my desk. It might as well be glued to my backstage handbook. Beyond the case formulas and the tables, it also just has great information on how to derive a load rating without using a case formula. 

It crosses everything you ever need to know about building with steel onstage minus the actual welding. If you need to build a 20' cantilever with a PSF of 150#... you can do that with this book.


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## erosing

Thanks Kyle, that is exactly what I am looking for, just bought it.


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## ajb

Structural Design for the Stage is a very good resource, but be prepared to spends some time with the book and pencil and paper before you start putting it to use. There's a lot of material to absorb if you haven't done any sort of structural design before. A big, BIG caveat about the book: It is only suitable for static designs. Dynamic loads are a whole can of worms apart. 

Another good resource for lumber is USDA FPL GTR-113 Wood Handbook: Wood as an Engineering Material Which you can also purchase as the Encyclopedia of Wood for about $15 if you prefer a dead tree copy. So far it's the best resource I've found on fastening wood.


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## tjrobb

I don't believe it covers plywood strength, but the "Backstage Handbook" has a lot of information such as what you are requesting. I have found it useful for a lot of random projects.


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## erosing

If you happen to have page numers that would be great, because then I missed it, but I don't think I did. It has the material weights, but I haven't seen anything related to the strength of stock goods other than rope and cable.


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## Footer

tjrobb said:


> I don't believe it covers plywood strength, but the "Backstage Handbook" has a lot of information such as what you are requesting. I have found it useful for a lot of random projects.



It does not have the proper tables to do load calculations. It has good info on the nominal sizes of lumber/steel and lbs per foot.


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## Traitor800

The problem with sheet goods and platforms for that matter is that the width is to large compared to the length to be able to use any of the basic beam equations for bending. The width would have to be closer to 1' for an 8' length in order to use the beam equations. Instead for like a 4x8 platform you would have to use a much more complicated 3D method for calculating bending. Not to mention the non uniform cross section that something like a platform would have.

But if you are doing bending calculations for wood, a pretty good base UTS to use is 2000#, and that works for plywood and most of the lumber that you would come across in theatre. just be sure to use a saftey factor of at least 5 for wood projects cause wood varies so much.

As for the strength of different shapes and cross sections, it all comes down to the area moment of inertia for the desired cross section, because the yield strength of a material is always the same.

-Chris


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## Footer

Traitor800 said:


> The problem with sheet goods and platforms for that matter is that the width is to large compared to the length to be able to use any of the basic beam equations for bending. The width would have to be closer to 1' for an 8' length in order to use the beam equations. Instead for like a 4x8 platform you would have to use a much more complicated 3D method for calculating bending. Not to mention the non uniform cross section that something like a platform would have.
> 
> But if you are doing bending calculations for wood, a pretty good base UTS to use is 2000#, and that works for plywood and most of the lumber that you would come across in theatre. just be sure to use a saftey factor of at least 5 for wood projects cause wood varies so much.
> 
> As for the strength of different shapes and cross sections, it all comes down to the area moment of inertia for the desired cross section, because the yield strength of a material is always the same.
> 
> -Chris



Which is the reason we have the triscuit. Much stronger design and much easier to calculate loads with.


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## robartsd

Traitor800 said:


> The problem with sheet goods and platforms for that matter is that the width is to large compared to the length to be able to use any of the basic beam equations for bending. The width would have to be closer to 1' for an 8' length in order to use the beam equations.


 
I know that this is an old thread, but I didn't want to see this information remain uncorrected. I found this researching triscuits.

The width isn't a problem (except that the equations all assume that any loading is distributed across the beam). The big problem is that nearly all engineering equations will be based on small deflections. Once you allow ANY beam to bend significantly (typically we use length/240 as a deflection limit) the effects of the bending on beam geometry needs to be considered.

BTW, design specs for plywood are freely available (registration required) from APA - The Engineered Wood Association. For triscuit engineering, see supplement 3. To me, these design specs are not quite as difficult as the NDS, but they are intended for engineers (for the stringers in the triscuit the design spec is still the NDS). The steel manual from AISC does seem to be better organized than the NDS, but because steel is more predictable, design of steel can be much more complicated—the less predictable the material properties, the more we make conservative simplifications and increase safety factors.http://www.apawood.org/pdfs/download_pdf.cfm?PDFFilename=managed/U813.pdf


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