March 8, 2011

Snow on the roof

Why did I tell you such a weird thing in the last post? The reason was the KAIT Kobo building you can see in the photos below.
External view. Photo from naoyafuji.

Internal view. Photo from brandon shigeta.

Is there anything remarkable in this building? Since the previous post had something to do with columns, you may make an educated guess...

There are many, many columns, exactly 305 steel columns in total. Careful, don't let them fool you. In fact, there are only 42 columns. But wait, didn't I write 305... where did the other 263 columns go?

They're still there, of course, they didn't disappear in the air. But they're not columns, they just look like columns. A column is not only a vertical constructive element. There's an additional feature it must fulfill: it has to be compressed. And these 263 ain't compressed at all. They're tensioned: the roof pulls them.

Such high number of supports was intended for architectural reasons. They limit the different spaces, and resemble a natural bamboo forest (which happen to be in Japan, like this building). Almost every single column (290 of them, to be accurate) has a different quadrangular shape, ranging from 16-by-145 mm, to 63-by-90 mm. If the thinnest of them (which is not even 2 cm thick!) was a real column, it would buckle. So, the question behind the structural concept was the one I asked you in the previous post: how to prevent such a thin column from buckling?

The "columns" would buckle when the roof is loaded...

And the answer is the same: it won't buckle if it doesn't buckle.

To achieve our slogan, the steel structure was built in two phases. First, the 42 real columns and the roof steel frame (made of 20 cm deep steel beams arranged in a 1.5 by 0.9 m grid). Then, the 263 fake columns were hanged from the girders, the roof was loaded with weights up to the snow load (the maximum vertical load the building has to stand), and then (and only then) the lower part of these 263 supports was fixed.

When the roof was unloaded afterwards, the roof structure went up (as you already know, with the previously applied "snow" load it was deformed), and consequently the 263 false "columns" were tensioned. By means of this peculiar strategy, these supports are supposed to be never ever compressed and consequently they will never ever buckle, they will always stand straight and resemble real columns to the profane eye, but no longer for you, right?


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