truss calculations

[theroo]

hi

 

just wondering if anyone knows any sites or perhaps can themselves tell me about the calculation of forces in trusses? particularly those that are used in flying in theatre?

 

thanks!

[Brian]

This is a real 'how long is a piece of string question'. I know how to do the calculations but there is no way I would ever do them for anyone else, I'm not qualified to do so. I have probably about 3000 pages of reference material on the shelf in front of me now on structural calculations.

[Pete McCrea]

I could in theory tell you the load on each chord having (oh sooo) nearly completed a Civil Engineering Degree. But as Brian says, I wouldn't do it for someone else to use for the basis of flying stuff of the truss. It comes down to basic analysis in terms of finding out the Bending moment/Shear forces/Axial forces in the members, that I'm sure we could detail if it's on a chord by chord basis.

 

If your after load charts to tell you how much a certain peice of truss can carry, then each manufacturer will have them for the relevant truss components. Try their websites.

 

However, and forgive me if I sound over cautious/harsh or not not planning on using it for a job, but if you have to ask, do you really have the necessary knowledge to do the job safely? I'd suggest that a rigger who is competent to do the job would know where to get the relevant information to complete the task. Forgive me if your asking for another reason, and not with the intent of rigging stuff. Get someone to train you and serve time with riggers learning the skill if you want to do it properly.

[Chris Higgs]

Get the operating manual and load chart for the relevant truss from the manufacturer.

You don't need to know anything else unless you are an undercover loss adjuster or barrack room engineer.

 

But seriously, if you need to know for some other reason, get the manufacturer to copy you the relevant parts of the product's structural report.

[theroo]

hi

 

haha, don't worry, I'm not planning on building a flying truss or anything, it is just for a project whcih I am doing.

 

But thanks for the concern :(

 

Could you help me with the names of some truss manufacturers? That'd be great so I can start to contact them.

 

However, while the load charts would be great, it is more of the actual calculations that I am interested in. ACtually, what I really need is the optimum shapes/angles and materials for building trusses.

 

Many thanks for all your help guys.

[Wilf dLampy]

Total Fabrications, based in Birmingham, are a truss manufacturer.

[Guest lightnix]

Total Fabrications, based in Birmingham, are a truss manufacturer.

And here is their website

 

You could also try...

 

Slick Systems

James Thomas Engineering

Optikinetics

[Pete McCrea]

Materials required to be strong in tension, and light to boot, hence the fact that Aluminium is the main material. The key design factor is to produce something that can take the 'moment' created by the load. This is accomplished by make in the second moment of area in the laoding plane larger, i.e. increasing the depth of the truss, or increasing the capacity that each member can carry. The other key area is the transfer of the load through the joints- often carried out by bolting or pinning the sections together. Various manufacturers have different ways of accomplishing this.

 

We were recommended 'Structural Mechanics, 2nd Edition', by Ray Hulse and Jack Cain (Plagrave Publishing year 2000, ISBN 0-333-80457-0) as our reading material, and it details the analysis of truss members. Might be worth a read if you want the really detailed stuff.

 

Little DJ

[Chris Higgs]

Two good books to read and re-read :

 

Prof. J.E. Gordon

"Structures and why things don't fall down" and

"The science of new materials or why things don't fall through the floor"

Haven't got the ISBN to hand because the books are at the office, but Amazon should help.

 

FYI: Since 2003, Total Fabs and Slick are the same company.

[MarcT]

Materials required to be strong in tension...

...and in compression too. A loaded truss span is likely to have the bottom chords in tension, whilst the top chord(s) are being compressed.

 

The key design factor is to produce something that can take the 'moment' created by the load. This is accomplished by make in the second moment of area in the laoding plane larger, i.e. increasing the depth of the truss

Indeed, but you shouldn't make the truss too slender (ratio of depth:width), or it could fail by out of (loading) plane buckling.

 

Prof. J.E. Gordon

"Structures and why things don't fall down" and

"The science of new materials or why things don't fall through the floor"

I'll second that. They were on my Engineering degree's part 1A Structures reading list 10 years ago, and are just as relevant today. Coincidentally, I found said list this morning whilst tidying the garage...

 

Regards,

Marc

[Pete McCrea]

Sorry. Was thinking more of the bottom chords. Yes, the top chords will be in compression, with the bottom chords in tension, assuming a point/UDL in the center of the span.

 

Simple first year lectures, but hey I finished my exams today so I'll allow myself some slack, and I have been celebrating (down the Students Union)!! I was never the best at the structural side of things.