The Marvelous and Wonderful World of Arch Bridges

Sam J. Klopping

Mrs. Bremer

Chemistry Honors

22 January 2013

The Marvelous and Wonderful World of Arch Bridges

Can you imagine a world without bridges? Just think of how difficult it would be to cross a river. You would have to drive to the river, put your car on a boat, and float across the blue inconvenience just to get to your job. Now with bridges you can admire the water as you cross it, or be scared and look at the floor of your vehicle. Bridges are basically as important as food, but not quite. The point is: everybody uses bridges sometime in there life, and traveling would be much more difficult than it has to be if nobody thought, 'Hey, I can put this log over this creek and then I wouldn't get wet!'

History of Arch Bridges:

Bridges have been around for a long time. The oldest man-made bridges date all the way back to the thirteenth century BC. These bridges were constructed by the ancient Greeks and Romans using mostly stone. The oldest arch bridge was erected in Greece in 1300 BC. It is known as the Mycenaean Arkadiko Bridge and is still standing today. It was built using a corbel arch, a design where successive levels of stone are slightly offset creating a steep arch.

The Pont du Gard Bridge in France was created by the Romans in the first century AD. It was used as an aqueduct to carry water to the city of Nimes. This bridge spanned 25 meters, which was a great distance for the time.

Another example of an ancient arch bridge, and perhaps the most important arch bridge in history is the Zhaozhou Bridge in China. It was constructed in sixth century AD. It was a milestone in bridge making for a few reasons. It has a span of 37 meters, which is longer than all of the bridges built by the Romans and Greeks at the time. It also had the flattest arch of the time. Lastly, the bridge was the first to be built using open-spandrels, meaning the roadway was support using columns and was not solid.

Once steel was discovered, almost all the bridges in the nineteenth century were built using it. The new material had one advantage over stone: bridges no longer had to be solid. Now bridges could be constructed easier and be lighter. A few noteworthy examples would be: the Eads Bridge in St Louis, which spans the entire Mississippi River, and the New River Gorge Bridge, the longest arch bridge ever erected at 518 meters.

In the twentieth century, prestressed concrete was introduced to the world. Arch bridges flourished with this new material. Prestressed concrete has the strength that stone has, but could be molded into any shape. This new material was eventually combined with steel to make the strongest of bridges, reaching the pinnacle of bridge-making in the modern world.

Some of the most famous arch bridges have been named previously, such as the New River Gorge Bridge (518 meters), which is the longest arch bridge in the world. A few other widely known arch bridges would be the Bayonne Bridge (510 meters) in New York and the Sydney Harbour Bridge (509 meters) in Australia, which are the second and third largest bridges respectively. The Salginatobel Bridge (90 meters), designed by the renown Robert Maillart, is known for its beauty and its aesthetically pleasing looks. Another commonly known arch bridge is the Ponte Vecchio. It stands in Florence, Italy, and still has shops built along, which was common in the Renaissance era.

The Process:

There are quite a few factors that play major roles when designing and building bridges. The architect has to decide which type of bridge would work best in the location. They also have to figure out which material to use. Another factor is how to make the bridge aesthetically pleasing while still creating a strong

bridge. Lastly, the architect must figure out how to do all of the previous stated objectives while still being cost efficient. It seems pretty tough to manage all of this, but this is only the thought process.

When deciding which type of bridge would work best in a location, we have to know the length of the gap. Are we trying to span a small gap, something under 40 meters? If yes, then we should probably go with a simple beam bridge or maybe a truss bridge if the loads are going to be heavy. If the bridge is going to be spanning a gap between 50 - 500 meters, then the arch bridge is probably the best way to go. The suspension and cable-stayed bridges should probably be the only bridges to exceed 500 meters. When the world needs a bridge longer than 2000 meters, someone will design a new type of bridge to accomplish the feat.

The next step is choosing which material to use. There are really only to options in these modern times: steel or prestressed concrete. Steel is lighter than prestressed concrete and can handle tensile stress much better than it. Prestressed concrete is heavier than its counterpart but manages compression in a way like no other material. Now you might be asking, 'Why can't we just combine both materials to make one super-material that can preform amazingly while under both tensile stress and compression?' Well it's been done. It is a material called reinforced concrete, and it does just that. It seems like reinforced concrete would be the only logical material to use, but it is also super heavy. When choosing a material for an arch bridge, we should probably choose steel for anything over 300 meters so it won't break from its