Thursday, July 10, 2003

I learned something new recently. I already knew that house foundations are primarily poured concrete, but they have a small amount of steel rebar in them to improve their strength. What I learned for the first time is that the reason these two materials are combined is because they bring different advantages. Concrete has tremendous ability to resist pressure; it can carry the weight of a house and its contents until doomsday. But concrete lacks shear strength: the strength necessary to resist breaking when twisted, lifted, or moved. In contrast, steel has tremendous shear strength but is not as good with compression strength. When the two are combined, their strength of one compensates for the weakness of the other. The point is well illustrated in the problems bedeviling Fallingwater, where the concrete cantilevers are finally crumbling under shear forces. If Wright's engineering firm hadn't snuck extra steel into the design behind his back, it would have collapsed long ago.

Now, there are a lot of ways this fact can be used as a metaphor -- a good marriage springs to mind -- but my mind is elsewhere. The upheavals in our life in August and September, and then again in December and January, were sudden jolts that tested the very limits of our shear strength. It was tremendously difficult, but we survived it. In times of upheaval, our steel held out. And I thought that would give me confidence in the strength of my personal foundation.

What has suprised me, I think, is that steel isn't enough. You have to have the concrete that can withstand the daily pressure: the unwavering, droning force of gravity. It just never lets up, never gives you a break, never ends. And I don't know that I have the strength of concrete.

 4:12 PM

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