Monday, February 18, 2013

Working on a tall building model to test in Wind Tunnel

18.2.13: We're designing three tall building models a metre high that can be used for airflow, resonance and seismic testing in a wind tunnel. The towers will have a litre can of water at top to test damping. Three models: core and outriggers, lattice facade, mega-braced frame . Here's the outriggers team! The purpose is to explore the role of the FACADE as a structural element.

diagram Gunel and Ilgin
One of the problems we have is the 'D'Arcy Thompson' one of SCALE (ex-Growth and Form). A tower that is ONE metre high is as different from one 100-200 metres high as a spider is from me. Throw the spider out of a first floor window, no harm done - it will throw out a silken thread and float safely to earth. Please don't do it to me! A 200th scale model is actually an 8 millionth of the real thing, considered by volume and mass.
   If you made a core of of one single piece of wood, it would be completely solid with no elasticity, and would topple over. We have to make a core that resembles a backbone of vertebrae, that can sway and bend. We have to post-tension it, because if needs to behave elastically and not just bend and stay bent. The building has to be firmly fixed to a baseboard, to simulate a strong foundation.
    We are going to try using bungee cord for the facade to make it behave elastically. Although it is tempting to make a facade out of clear plastic, imagine how solid that would be if translated to full scale - the only thing that may resemble the behaviour of glass in a real tower is the thinnest cling-film. Many of the structures are being bolted (so that they flex). The bolts must not be too tight or the structure is too stiff to behave elastically. If they are too loose, it is slack and deforms plastically. So we are using spring washers, self locking bolts and may have to use some of the bungee cord as bracing to restore the shape.
    All interesting explorations!! (More pictures will follow)

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