Can you imagine how hard it would be to cross a river without these structures? Take the Mississippi, for example. Even taking a boat would be difficult! One of the most popular types is the suspension bridge. They can also be beautiful and elegant. Suspension bridges get their name from the fact that the roadway is suspended by cables from two tall towers. Most of the weight is supported by the two towers.
They, in turn, pass the compression forces from the cables directly into the ground. Suspension bridges also have smaller cables called suspenders.
These run vertically from the deck up to the main supporting cables. This creates graceful arcs between the towers and down to the ground. The towers of a suspension bridge can be fairly thin. The force of the deck pulls inward on the towers. At the same time, the main support cables extend beyond the towers to anchor each end.
These are usually solid rock or heavy concrete blocks secured underground. The anchors pull outward on the towers with an equal force to that of the deck. This centers the weight of the bridge on the tower. Early forms of this structure had design flaws. For example, some used chains for the main cables. These could collapse if one link broke. This problem was solved by making main support lines out of bundles of high-strength steel.
Several parts of the bundle can fail and the bridge will stay standing. Some early suspension bridges also had thin and unstable decks. When hit by heavy winds, they would shake themselves apart. Today, the structures have thicker, rigid decks. Suspension bridges seem like marvels of modern engineering.
But the first ones were built by the Incas over years ago. These were made of twisted grass and often spanned over feet.
They were used to cross deep mountain gorges in Peru! Have you ever crossed a suspension bridge? Have you ever seen one from a distance? We hope today's Wonder of the Day bridged the gap in your understanding of basic engineering! Learn even more when you explore the following activities with a friend or family member:.
Thank you so much, Hunter c.! Cables consisting of many strands of wire for suspension were used instead of chains for the first time in by French engineers. Soon John Roebling, American inventor, found a way to spin the cables at the place of building instead of transporting them prefabricated. He also invented rigid deck platform which is stiffened with trusses. Since then suspension bridges became popular because they allowed to bridge spaces that could not be bridged with conventional methods.
Its advantages are that it can be made with longer spans than with other types; it is cheaper bridge type even with longer spans because it uses less material; during construction it does not require access from below so it doesn't matter much what is below nor how high is bridge; it is more earthquake-proof than other types; and it can be modified easily to accommodate wider vehicles or to add additional lanes. Where can you find examples of compression hint: think of the empty can and tension hint: try a game of tug of war.
Using lots of math, civil engineers position the parts of a suspension bridge so compression and tension work together to hold up some of the world's longest spans. With a partner and some common household items, you be able to see what it feels like to be a suspension bridge—and compare the strength of a suspension bridge to a beam bridge. Background People have been building suspension bridges for more than years to cross the widest rivers and canyons.
Today, you can still find suspension bridges deep in the remote jungle as well as in most major cities. In the U. The main parts of a suspension bridge are its towers, cables, decking and anchorages. As you might guess, the long cables are the unique part of a suspension bridge. To start, face your partner.
Don't let go! Do you feel a tug? What is the force associated with pulling? This is tension, which suspension bridge cables use. Now slowly, carefully lean toward each other. What kind of pressure do you feel now?
Structural Failure Some bridges have in the past suffered from structural failure. This may be combination of poor design and severe weather conditions. When it was opened in , the Tacoma Narrows Bridge was the third longest suspension bridge in the world. It later become known as "Galloping Gertie," due to the fact that it moved not only from side to side but up and down in the wind.
Attempts were made to stabilize the structure with cables and hydraulic buffers, but they were unsuccessful. Eventually on November 7, , only four months after it was built the bridge collapsed in a wind of 42 mph.
The bridge was designed to withstand winds of up to mph. Some experts have blamed the collapse of the bridge upon a phenomenon called resonance.
When a body vibrates at its natural frequency it can shatter.
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