Prestressed Concrete Beams

Concrete is awesome under compression. Concrete can take a huge amount of stress without failing. Concrete, however, is pretty awful under tension. Iron is awesome under tension but not so great under compression - eventually failing in pretty spectacular ways. Combine the two, however, and you get some pretty outstanding results.

One of our master teachers, Andy Nydam, tells a great story about a mother - I don't want to suggest that it was his mother because I wouldn't bet his reputation on that detail - who allowed one brother to payback a transgression by the other brother by using a single towel hit. The mother envisioned a single snap with a towel, but the wronged brother laid the towel out overnight in the freezing weather soaked in water. Ice - bad under tension, good under compression...towel - bad under compression, good under tension...composite frozen towel - good under both.

I'm not saying; I'm just saying.