# The Mathematical Bridge of Cambridge

The footbridge shown above crosses the river Cam on the campus of Queens’ College in Cambridge, England. The Mathematical Bridge was first built in 1749. It has a nice arch, but there are no curves in the design- all the timbers are completely straight.

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The Mathematical Bridge is constructed out of interlocking pieces of timber. Each rib of the superstructure are set at tangents to the circle describing the underside of the arch of the bridge. In the arch itself, each member is under compression with little or no lateral force that could cause bending. Where the main members cross, the wood joint transmits the compressive stress from one member to the next, with a bolt serving to hold the joint together laterally, rather than itself carrying any stress. There are also radial members which both support the top rail and lock all the overlapping tangents into a rigid truss. The load bearing deck is supported by horizontal cross-beams attached to the bottom of the radials, close to the junction of two tangents. When a load is applied the vertical forces get distributed along the tangents as compression opposite to the compressive forces from the tangents, thus balancing each other.

The rest of the article on the bridge at Amusing Planet is less technical, and goes into the history of the design, which has been used elsewhere, and may have originated with Leonardo da Vinci.

(Image credit: Flickr user Michael Jefferies)

Source: neatorama

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