My name is Lauren, and Im a secondary school student in Ontario. For my gr11 advanced math class I have to find out how and why parabolics are used in arch bridges and write 3 paragraphs on it. People who cohse satelites and whatnot are lucky - I've found a ton of info, but for arch bridges there seems to be nothing.

PLEASE HELP ME!!! I'm soooo desperate becasue I cant find anything except pictures! Thank you. Looking forward to your response,

~Lauren~

Hi Lauren,

There are two curves with very similar shapes that are important in bridge construction. One is called a catenary and the other a parabola. The best two references I could find have to do with suspension bridges, but the princilpe is the same. If you hang a cable between two towers, as you see in power lines, the curve you see is a catenary. If you hang a bridge from a pair of such cables by vertical cables that are uniformly spaced along the length of the bridge, then the curve of the suspension cables becomes approximately a parabola.

The first reference I found, Suspension bridges says:

"For the suspension bridge in general the roadway is very nearly a uniformly distributed load, and each cable hangs down in a curve closely approaching that of a parabola. Perhaps that is why the suspension bridge is such a lovely imposing structure."

In the second reference if you scroll down to "Catenary and parabola" there is a further explanation.

I also found a page with definations of terminology in the bridge and tunnel induster that saya:

Parabola
a form of arch defined by a moving point which remains equidistant from a fixed point inside the arch and a moving point along a line. This shape when inverted into an arch structure results in a form which allows equal vertical loading along its length. A famous example of this shape is the Gateway Arch in St. Louis, MO. I hope this helps,
Harley
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