# Calculating the Specific strength for the rod

Eagle9
Imagine the skyscraper and the very long rod placed on its top that rotates from horizontal position to upwards.
http://img109.imageshack.us/img109/4817/fhfn.png [Broken]
I would like to know how is it possible to calculate/ascertain the maximal length and minimal width of the rod made of some certain material, let’s say steel. For example, is it possible to hold the rod with the length of 5 km horizontally (not by hands of course )? The rod will be broken? What, if I need to hold much longer rod (let’s say 50 km)? Which material should I use? How can I calculate its maximal possible length? As far as I know I need to use the values of Specific strength, right? In Wikipedia I found the article: http://en.wikipedia.org/wiki/Specific_strength and the values for various materials, then what? Let’s assume I am using the carbon nanotubes and I created the rod (not the elastic ribbon like Space Elevator’s cable), how can I calculate its possible maximal length? Is there any formula for this purpose?

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