Tuesday, May 25, 2010

Compression and Tension

FLG often mentions his stint as an engineering student. Well, today he walked by some workers lowering concrete cylinders into the street. For what purpose he wasn't sure.

However, it did remind him that while concrete is very good at dealing with compression it's pretty bad at tension. This means that concrete is a great material for pillars, but terrible for the spans connecting those pillars. The solution to this problem is often to place reinforcing steel bars (rebar) in the concrete. The steel then takes the tension forces and the concrete deals with compression.

Even more interesting, at least to FLG, is how the Romans dealt with the poor way stone and concrete deal with tension -- the arch. The arch is really two different semicircles that are falling into each other. This transforms the tension into compression and voila, no more problems with using stone and concrete.

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