Different Types of Bridges Essay -- miscellaneous

Different Types of Bridges The quest for travel has always been one that man has tried to conquer. First, he traveled on foot, and then developed methods of transportation such as boats, but one of the first obstacles that he had to overcome was getting across rivers, waterways, and canals. Today, bridges have become a part of everyday life; hence without them, people would have a much more difficult time going from one place to another. In the United States alone, there are more than half a million bridges (History of Bridges 1). Although bridges have been in existence since ancient times, they were not first made by man. Nature actually made the first bridges by toppling logs across streams. This was considered the first beam bridge as the flat rocks were used to support the log. Then, the water eroded the rocks and eventually a stone bridge was formed. The ancient Romans built arched bridges because they needed roads and bridges to connect the sections of their empire. The original swing bridge, from which the suspension bridge was produced, was a simple vine that swung people over the water. From these beginnings, men created four main types of bridges. To begin with, beam bridges, also known as girder bridges, are one of the easiest and simplest types of bridges to build. In ancient times, people used to make these bridges out of granite. Beam bridges can be made by putting a wooden plank over an area needing to be crossed. To get across larger areas, piers or supports can be fabricated up from the river bed to hold up a couple of beams. The piers of the girder bridge have constant pressure on them. Therefore, the beams, which are usually made out of concrete or steel, have a lot of strength so they do not crumble due to the heavy load. Many beam bridges are made of pre-stressed concrete. This concrete has steel rods inside of it, which help resist tension. When the weight pushes down on a bridge, the top of the beams are pressed together creating compression, while the bottom edge is stretched and causes tension. Beam bridges are not practical in cities with a lot of high rises, because the bridge has very low clearance. The bigge st limitation of the girder bridge is its length. The farther apart the piers are, the weaker the bridge gets. Beam bridges are good to use on spans of up to two hundred feet ( How Bridges Work 1). A bridge of greater... ... long way (Bridges 3). A cable-stayed bridge is used to cross medium lengths, which are approximately five hundred feet to two thousand eight hundred feet (Bridges 3). The cable-stayed bridge requires less cable than a suspension bridge, and is much faster to build in comparison to suspension bridges. Cable stayed bridges are supported by stave towers. These towers are ‘A’ shaped, and absorb almost all of the bridge’s compression. Unlike suspension bridges, cable stayed bridges only have two towers and do not need any anchorages. Now that man has overcome the obstacle of getting across rivers, canals, and waterways efficiently, it is now time to perfect these human creations so no more mishaps happen. Even though people keep hearing about collapsing bridges, they still use them because it has become a part of their everyday life style. Without bridges, people would have a difficult time getting from one place to another. It could be done by means of a ferry or other boat, but that is time consuming and a real pain in the neck because once a person gets across the river or canal, they would have to walk everywhere. So, without bridges, things would not be the way they are today.