There are more than half a million bridges in the United States, and you rely on them every day to cross obstacles like streams, valleys, and railroad tracks. But do you know how they work? Or why some bridges are curved while others are straight? Engineers must consider many things -- like the distance to be spanned and the types of materials available -- before determining the size, shape, and overall look of a bridge.
Since ancient times, engineers have designed three major types of bridges to withstand all forces of nature.
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| Cantilever bridge: Firth of Forth |
The truss bridge...consists of an assembly of triangles. Truss bridges are commonly made from a series of straight, steel bars. The Firth of Forth Bridge in Scotland is a cantilever bridge, a complex version of the truss bridge. Rigid arms extend from both sides of two piers. Diagonal steel tubes, projecting from the top and bottom of each pier, hold the arms in place. The arms that project toward the middle are only supported on one side, like really strong diving boards. These "diving boards," called cantilever arms, support a third, central span.
Check out the forces that act on truss bridges!
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| Ancient Roman aqueduct |
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| Suspension bridge: Golden Gate Bridge |
Now that you've mastered the bridge basics, test your bridge-building skills in the Bridge Challenge!
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