One of the four main types of bridges is the suspension bridge. These bridges are generally long and somewhat imposing. The towers that are essential to the structural integrity of these bridges loom large. They make these spanning structures hard to miss.
The towers are not just for effect. They are the support for the cables that stretch from the land, up and over the towers, and back to the land. In turn, these cables provide the support for the vertical cables that extend from them to the deck of the bridge. The deck of the bridge is suspended from the cables — a suspension bridge.
As you examine a suspension bridge, you will see that, as a result of the cables being firmly anchored on either shore, there is a finite amount of cable to work with. The structural cables – the ones going up and over the towers – form a parabola between the towers because the weight of the deck is evenly distributed along the length of the cable.
The weight of the deck causes the cables to be in tension – meaning they are pulled downward. The bridge doesn’t collapse because the foundations of the towers are beneath the bed of the body of water; the towers stand strong as the forces are conveyed through them.
Part of the suspension bridge is a cantilever. We’ll speak about that further in a future post.