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Completely O/T - minimum weight structures


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#1 Greg Locock

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Posted 05 April 2013 - 02:08

This is a really neat bit of work I once came across at uni, I suggest you start at the back, as that has the punch line - a graph of structure volume vs aspect ratio for a cantilever.

http://naca.central....arc/rm/3303.pdf

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#2 Bloggsworth

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Posted 05 April 2013 - 11:05

Didn't understand a word...

#3 Greg Locock

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Posted 07 April 2013 - 00:24

Didn't understand a word...

A famous structural engineer once said that the worst thing that ever happened to the analysis of structures was when the idle French mathematicians of the 18th and 19th century got involved.

It is true that you can get amazingly good results in both structures and statistics (another playground) by sticking to basics and approximating.

But, if you want to know what a minimum weight structure would actually look like, that paper tells you.


#4 Kelpiecross

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Posted 07 April 2013 - 03:39

The graphs and drawings at the end of the paper are very interesting - unlike the preceding gibberish (gibberish to me anyhow).

The Michell structures at the end remind me very much of the "iron bridge" at Ironbridge. I don't know if the "iron bridge" structure was calculated (certainly calculus and mathematics were pretty advanced by 1779 when the bridge was built) - or it was built by the "that looks about right" method.

#5 Lee Nicolle

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Posted 07 April 2013 - 09:32

It would not download for me [steam driven internet. Grrr!] but my observation is that in the past they built things very strong, probably too strong but their standards were different too. some old stone bridges built in the horse and buggy days carry semi trailers! Overenginered, you bet.
A lot of steel/iron bridges are the same. They carry probably 3 times the weight originally envisaged.
There was a TV series, 'mighty structures' or similar that showed the building of some of these, it also showed the failures.
In my area the 'engineers' have built major and minor bridges that have lasted less than 20 years. Concrete and steel which have spalled terribly. One was load limited at 2 ton, after walking under it I advoided driving over it!
The major one over the Murray had a 3 tonne limit and the trucks were going 30km out of their way to go around it. This on the main road to the Riverland and Sydney. That was a very major 'Ooops'

#6 Tony Matthews

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Posted 07 April 2013 - 10:37

There can't be many more complex stone structures than the great cathedrals of GB and the Europe, and although some collapsed during the build - DAMN! Oh well, start again - once up they have staid up. Not many buildings of such size last over a thousand years, and not many recent ones will last a couple of hundred, planning allowing.The concept of the flying butress fascinates me, wonderfully elegant solutions to a serious problem. I don't often enter a historic cathedral, but when I do I tend to fill up, but with admiration for the architects, builders, carpenters and stonemasons, not for anything else.

#7 Kelpiecross

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Posted 07 April 2013 - 14:03


I am a bit surprised to see that the members in the Michell structure (Fig.28) are curved - I would have thought straight would be stronger - unless maybe they wanted to use as few joints as possible and long one-piece members.

I can see applications in bridges and buildings etc. - but in cars?


#8 Greg Locock

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Posted 07 April 2013 - 22:14

The line about the French was either Jacques Heyman -author of many books on structural design http://www.goodreads....Jacques_Heyman
and also my lecturer, or JE Gordon, who wrote the two books on Structures and Materials that everybody who is interested should read.
http://www.goodreads...arch_type=books

I'm guessing it was Gordon.



#9 Greg Locock

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Posted 07 April 2013 - 23:37

did you go to uni there?

Yes, Heyman's lectures were very popular, even the architects turned up for some of them!