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,


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:

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,
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