This provides a very good visualization of how the members in a tower respond to the forces put on when a top load is applied, and as the saying goes, a picture is worth a thousand words. Thanks for providing, and adding to 'the book of knowledge' we're compiling here..USCEngr wrote:This may be a bit late to help some students but this short vid shows some of the basic elements of the towers and their purposes.
https://youtu.be/Uv0G4OwRWCw
There are essentially three different elements in a tower: the legs, the horizontal truss and the diagonal truss. Which elements are in compression and which are in tension? Do compression elements or tension elements need to be thicker? And which elements will eliminate bulging/bowing and which elements reduce torquing? Building a straw tower, a builder can add and remove each element and get answers to these questions. Engineers would create computer simulation models but a straw model works just as well.
Speaking of words, a couple of nomenclature things to clear up, just so we’re all on the same page. First, “truss” is not the correct term for the individual bracing members. From Wikipedia:
In engineering, a truss is a structure that "consists of two-force members only, where the members are organized so that the assemblage as a whole behaves as a single object". A "two-force member" is a structural component where force is applied to only two points.
So, "horizontal brace", or "bracing member", or "ladder", and "diagonal brace", or "bracing member", or "X".
Second, understanding the “bulging/bowing’ you note is critically important in designing a tower. Its called "buckling", and it is how long thin columns, when put under axial compression loading, fail. If you go back into this thread (and other threads in the towers forum), you will find pages and pages of detailed discussion of how buckling works, and how to do analysis and design to increase the buckling strength of the legs (so that the tower can hold the design load). One of the very basic design decisions to be made is the optimal tradeoff between lighter, less stiff legs with more bracing, or heavier, stiffer legs with less bracing; how to this is discussed in detail. The effect of size (cross section) on buckling strength (of members under compression load), and tensile strength (of members under tensile load) is discussed. The important relationship of density to strength is discussed.
On page 2, there is a detailed discussion of the basic mathematical relationships at work, including the very important ‘inverse square relationship’ between a column’s length and its buckling strength
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On page 4, some more basic concepts for design and construction are presented and discussed
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Then, on page 10- there is a multi-page attachment with drawings on bracing; specifically a ‘ladders and Xs' configuration.
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And, last, if you go way back to the archives; to the 2011 towers forum, there is some very good, very detailed discussion and analysis of various bracing system; configuration, and performance against various criteria.
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Putting the detailed information that has been compiled here in this forum since the season started together with the visuals of what’s going on you’ve provided, provides everyone with a comprehensive understanding of how to proceed, how to be ….as competitive as you want to be. Every year I’m surprised at the number of people who find the tremendous resource this forum is, but don’t bother to go back and ‘read the book.’ And once again, I urge you, and anyone who is working on how to ....create a 'good' tower', how to improve the performance of your tower from what you've achieved so far to take the time to digest all the info that we've collectively put together here.