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Increase natural frequency of truss tower

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Ferdissss
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Increase natural frequency of truss tower

Hi, 

We played a 'game' in class at uni, but I was never able to finish it or understand it completely. Could anyone help me? 

 

We were given a simple truss tower (Picture below). It is 4x4x30m. I was not able to attach the file, sorry.

The task/game was to get the natural frequency over 5 Hz, timber utilization over 1(I guess that means ratio under 1, right?) and a total weight of max. 25 000 kg. 

 

Rules of the game: 

- Not allowed to add materials. Only allowed with timber GL28(glulam): 100x100, 100x200, 100x300, 200x200, 200x400, 300x300. 

- We can add as many elements as we want, but not delete existing elements or add new supports. 

- We can change the type of release. 

 

I added a simple bracing(one diagonal) on all four sides, at all the 'floors'. The natural frequency was then 3,3 Hz. No matter what I tried from here, my frequency got lower.

 

 

vildehog_0-1702060520638.png

 

 

Any thoughts?

Thank you! 

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Message 2 of 3
Simau
in reply to: Ferdissss

@Ferdissss 

At each level add 4 interior diagonals

 

Frq_increase.jpg

 

M. Agayr
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Message 3 of 3
Simau
in reply to: Simau

@Ferdissss 

Use a mixture of X ,inverted V, and interior diagonals with the smallest section (100x100)

frq increase.jpg

M. Agayr
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