The Physics of Bridges

While checking my e-mail this morning, I was intrigued by a link to a Popular Mechanics page titled "The World's 18 Stranges Bridges" and of course I went to check the website. I saw some really striking (both in architecture design and function) bridges that really seem to defy physics, but at the same time don't since these structures are still up and running in the world today. Here are some of the pics that I liked the best:

Langkawi Sky Bridge in Malaysia

Juscelino Kubitschek Bridge in Brazil

Millau Viaduct in France

Henderson Waves in Singapore

Rolling Bridge in London

Bridges are typical structures that must follow the laws of physics in order to function. While some of these bridges seem like the architects placed safety and fuctionality as secondary issues below aesthetic design, these infrastructures still follow the laws of physics in essence. Generally, bridges involve a number of physics concepts including Newton's Laws, Resonance, Forces, and more. Bridges typically come in three different groups: beams, arches, and suspension bridges. Each design has its own physics concepts and challenges behind it. Suspension bridges typically span longer distances, with arches coming in second, and beams last. The difference lies in how the three types of bridges deal with the two major forces of COMPRESSION and TENSION (like a spring). The best way to deal with these forces is to either dissipate or transfer them.

For instance, arches are good examples of dissipation. The design itself, a semicircular structure with supports on either side, naturally turns the weight of the object from the center of the deck to the abutments. Because compression lines are pushed outward along the curve of the arch and towards the abutments, the force of compression is dissipated, which means the force is not concentrated on one area, but is rather spread out to a larger region so that one part does not bear the brunt of the force. 

On the other hand, suspension bridges are great examples of transfering the effects of the forces of compression and tension. To transfer force is to move it form an area of weakness to an area of strength. In a suspension bridge, the towers, through which the cables are connected to, support majority of the bridge's weight. The cables feel the force of tension, but the force is transferred to the abutments or the towers, all of which are entrenched in the ground, in which the force dissipates into overtime. The compression force felt by the road is also transferred in the same manner.