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Re: Wood

Postby dholdgreve » March 14th, 2018, 6:16 am

I was also wondering if 1/16 x 1/32 x 36 balsa would be high or medium density. I use medium and am wondering if high density bracing with lighter beams would be better.
Lightening the density of the columns, and increasing the density of the X braces "does not compute... It's an apples and oranges scenario.

If you are going to lighten the density of the columns, the correct trade-off is to increase the number of tiers of X braces, thus decreasing the space (unsupported column length) between the Xs. Technically, by increasing the number of Xs and decreasing the length of unsupported columns, the load on the individual X brace members goes down, so if anything, you may be able to go even lighter on the X braces.

Case in point... I once saw a young man from Clio MI present a tower for competition... It had no ladders, but it had like 32 X braces on each side! Ya... I thought it would be too heavy too!... It weighed an amazing 5.85 grams and carried the full load. He won by a landslide!

The only reason to increase the density of the Xs (IMHO) is because you have suffered consistent failures of the X bracing pulling apart (tension failure), or some sort of shear failure.

As has been mentioned previously, when the lower columns are leaned in, the faces of the columns are no longer co-planar. All column faces now point in toward the center of the tower slightly. Using 1/32" thick material as a tension band near the bottom of the tower "may" result in shear failure at the point where the tension band meets the column because as the column pushes outward, the tension band is not perfectly aligned with the column face. To compensate for this, you "may" want to either increase the density of the 1/32" piece .or increase thickness to 1/16" on these tension pieces.
Dan Holdgreve
Northmont Science Olympiad

Dedicated to the Memory of Len Joeris
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