Strengths of different truss patterns
- Thread starter hello183
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JasonK
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triangles are generally strong then other shapes. however it would matter what the expect loading patterns would be to ID the best trussing. it is also a weight/strength trade off, different patterns make different choices for that. (and some might just be 'this is what I wanted' or 'this is good enough and easier to build').
JasonK
Participation Award Recipient
I would need to refer you to a mechanical engineering text book for that discussion (as it can get rather complicated). I touched on the subject in college, but that wasn't my primary focus.
quorneng
Master member
hello183
In the great majority of truss designs the limiting factor for any given weight is the compressive strength of each part. A truss design with long individual elements will be likely fail in compression before a truss with shorter but thinner elements with the same total weight, however lots of shorter elements means more joints and proper structural joints ca be difficult to achieve.
Unfortunately you would have to get involved in both structural stress analysis and the strength of materials to determine which truss design gave the best possible strength to weight.
Like most things in model aeronautics the answer is either experience coupled with experimental "trial and error" or to simply copy what others have done in similar applications.
In the great majority of truss designs the limiting factor for any given weight is the compressive strength of each part. A truss design with long individual elements will be likely fail in compression before a truss with shorter but thinner elements with the same total weight, however lots of shorter elements means more joints and proper structural joints ca be difficult to achieve.
Unfortunately you would have to get involved in both structural stress analysis and the strength of materials to determine which truss design gave the best possible strength to weight.
Like most things in model aeronautics the answer is either experience coupled with experimental "trial and error" or to simply copy what others have done in similar applications.
Thank you. I will use the trial-and-error method. But when wings are built, isn't it stronger when the spars are spread apart more? So, for trusses in a fuselage for example, can't it be stronger if the longerons are spaced farther apart, even if it makes the uprights and trusses a bit longer?
JasonK
Participation Award Recipient
the strongest 'form' would be solid material [IE a completely solid wing]. The goal of trusses is to get most of that strength at as small of a fraction of the weight as possible. by removing material you will decrease strength. However, the goal is to find that balance point between reduced strength and reduced weight that gives you the best outcome.
Think about an I beam, it is weaker then if it was solid, but it might be 90% as strong but at 30% of the weight. Building trusts is the same type of idea.
@hello183, I am no truss expert. But I have some experience with structures and bridges. @JasonK is correct, the goal is to lighten a structural member by reducing it to its bare minimum. Triangles are the fewest-parts that are stable and tend to Yield a light structure.
but the key to success is understanding the load path.
Typically in a bridge, the travel surface (load bearing functional part) rests on a flange (top or bottom) member of the structure and this tends to distribute the beam load to the junction points that thransfer through the beams simple as compression or tension. by changing the configuration of members, you can sometimes furth reduce the member size/wt. in a flexure member like most bridge structures, or cantilever structures like a wing spar, the load is highest in the outermost surfaces
Bridge Trusses:
Wooden (residential) Trusses:
but the key to success is understanding the load path.
Typically in a bridge, the travel surface (load bearing functional part) rests on a flange (top or bottom) member of the structure and this tends to distribute the beam load to the junction points that thransfer through the beams simple as compression or tension. by changing the configuration of members, you can sometimes furth reduce the member size/wt. in a flexure member like most bridge structures, or cantilever structures like a wing spar, the load is highest in the outermost surfaces
Bridge Trusses:
Wooden (residential) Trusses:
@JasonK, thank you for explaining it like that. I had a hard time understanding the balance the weight to strength thing, but I understood the example that you said about the I beam.
@FoamyDM, why don't some of the truss designs in your picture have triangles in them? the lattice and the double intersection warren don't. They're more like diamonds. I thought trusses only use triangles because they are usually the strongest shape?
@FoamyDM, why don't some of the truss designs in your picture have triangles in them? the lattice and the double intersection warren don't. They're more like diamonds. I thought trusses only use triangles because they are usually the strongest shape?
JasonK
Participation Award Recipient
That gable has 6 triangles and looks like one of the weaker options there (at least to me).
Also, those were examples of different trusses, not a 'only these shapes work' situation.
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