How Does This Thing Stand Up? ~regarding Snelson’s Needle Tower

by Susan Lowell

When I first started to really look at
Kenneth Snelson’s Needle Tower outside of The Smithsonian’s Hirshhorn Museum in Washington DC, the question that came to mind was: how does this thing stand up?

Tensegrity structures break a fundamental rule we have (well, maybe a few fundamental rules): the solid pieces do not touch other, yet the Tower rises. What is going on?

Not only that, but the compression struts are not horizontal to the ground and do not line up one on top of the other. Instead, they are at 45° angles and a zigzag this way and that.

The whole thing just doesn't make sense.

And yet, the Tower rises.

Our first challenge is just being able to comprehend what a tensegrity structure is and how it works, since we have never encountered anything like it before (except, of course, in nature).

So, how does it stand up? It doesn’t.

It might be more accurate to say it stands
out. It is fully expanded. In some ways (but not exactly), it’s like a balloon: the compression struts pushing out against the tension cables which are pulling in, much like compressed air in a balloon pushes out on the rubber casing which is pulling in.

An inflated balloon is structurally independent of gravity, so it does not really stand "up." You can turn it whichever way you want and as long as you can stabilize the part that meets the ground by connecting it to ground, the physics of the independence of the structure allows it to hold its shape.

Tensegrity structures work the same way. The Needle Tower stands up because the three struts at the bottom of the tower are anchored to the ground. But, it could just as easily be "stood" on its side, or upside down, or even at some funny angle stretching out obliquely into space.

Take a look at some of
Snelson’s other sculptures, such as his Dragon and you will see what I mean. Or, watch footage of the needle tower being put up. It is completely assembled on its side and then, much like an obelisk, it is pulled into the upright position.

Unlike the obelisk, at no point is its physical integral structure threatened in the process of being stood up.

There is no internal shear occurring.

But that discussion is for another day.

For the moment, just recognize that in terms of their structural integrity, tensegrity structures, like balloons, are gravity independent and omnidirectional.

So are we.