Bridge+notes

**Bridge:** A link or connection between two objects - usually places either side of an obstacle, such as a river, chasm, or estuary.  A bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle. Designs of bridges vary depending on the function of the bridge, the nature of the terrain where the bridge is constructed, the material used to make it and the funds available to build it



**Are all bridges alike?**
There are six main types of bridges:
 * Beam Bridges
 * Cantilever bridges
 * Arch Bridges
 * Suspension bridges
 * Cable-stayed bridges
 * Truss bridges

Bridges are usually made of concrete, steel, cement, iron, wood, stone and/or metal. Bridges connect one place to another. A bridge's //economic efficiency// will be site and traffic dependent, the ratio of savings by having a bridge (instead of, for example, a ferry, or a longer road route) compared to its cost. The lifetime cost is composed of materials, labor, machinery, engineering, cost of money, insurance, maintenance, refurbishment, and ultimately, demolition and associated disposal, recycling, and replacement, less the value of scrap and reuse of components. Bridges employing only compression are relatively inefficient structurally, but may be highly cost efficient where suitable materials are available near the site and the cost of labor is low. For medium spans, trusses or box beams are usually most economical, while in some cases, the appearance of the bridge may be more important than its cost efficiency. The longest spans usually require suspension bridges.
 * What are they made of?
 * What are they connecting?
 * <span style="color: #008080; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">How is the span between their piers or towers?



<span style="color: #008080; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">2. What social and/or political benefits can bridges provide to places?
<span style="color: #008080; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">A bridge is designed for trains, pedestrian or road traffic, a pipeline or waterway for water transport or barge traffic. An aqueduct is a bridge that carries water, resembling a viaduct, which is a bridge that connects points of equal height. A road-rail bridge carries both road and rail traffic. Bridges can improve communication, popularity and the quality of life in the places they are built. <span style="color: #008080; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">The first bridges were made by nature itself — as simple as a log fallen across a stream or stones in the river. The first bridges made by humans were probably spans of cut wooden logs or planks and eventually stones, using a simple support and crossbeam arrangement. Some early Americans used trees or bamboo poles to cross small caverns or wells to get from one place to another. A common form of lashing sticks, logs, and deciduous branches together involved the use of long reeds or other harvested fibers woven together to form a connective rope capable of binding and holding together the materials used in early bridges. <span style="color: #008080; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Bridges provide benefits to people living on either side of the bridge. <span style="color: #008080; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Some of the benefits of bridges are obvious: supplies of food and traded goods can get across an obstacle or through difficult terrain in a shorter time. <span style="color: #008080; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">This means that, in economic terms, the cost of travel and trade falls and the financial benefits of increased social cohesion and sharing resources rise. Other longer-term payoffs from easier travel, which is crucially dependent on good bridges, come as a result of increased opportunities to share ideas – intellectual, political and religious. <span style="color: #008080; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Today bridges allow easy travel across major rivers and estuaries, over the new obstacles of motorways and railway lines, and between neighbouring islands. International trade and travel depend on shipping and air routes, but efficient distribution networks depend on bridges.
 * <span style="color: #008080; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Why were the bridges built?
 * <span style="color: #008080; font-family: 'Palatino Linotype','Book Antiqua',Palatino,serif;">Did they provide benefits? To whom? Why?