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Many beam bridges that you find on highway overpasses use concrete or steel beams to handle the load. The size of the beam, and in particular the height of the beam, controls the distance that the beam can span.
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www.howstuffworks.com/bridge2.htm
www.howstuffworks.com/bridge2.htm
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Beam Bridges - Design Technology ... A beam or "girder" bridge is the simplest kind of bridge. In the past they may have taken the form of a log across a stream but today they are more familiar to us large box steel girder bridges. There are lots of different types of beam bridges.
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www.design-technology.org/beambridges.htm
www.design-technology.org/beambridges.htm
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But even the best materials can't compensate for the beam bridge's biggest limitation: its length. The farther apart its supports, the weaker a beam bridge gets. As a result, beam bridges rarely span more than 250 feet.
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www.pbs.org/wgbh/nova/bridge/meetbeam.html
www.pbs.org/wgbh/nova/bridge/meetbeam.html
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The beam bridge... consists of a horizontal beam supported at each end by piers. The weight of the beam pushes straight down on the piers. The farther apart its piers, the weaker the beam becomes. This is why beam bridges rarely span more than 250 feet.
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www.pbs.org/wgbh/buildingbig/bridge/basics.html
www.pbs.org/wgbh/buildingbig/bridge/basics.html
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Beam bridge - Wikipedia, the free encyclopedia
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Beam bridges are the simplest kind of bridge today. They are a direct descendant of the log bridge, now more commonly made from shallow steel 'I' beams, box girders, reinforced concrete, or post-tens...
en.wikipedia.org/wiki/Beam_bridge
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Bridge - Wikipedia, the free encyclopedia
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A bridge is a structure built to span a valley, road, body of water, or other physical obstacle, for the purpose of providing passage over the obstacle. Designs of bridges vary depending on the func...
en.wikipedia.org/wiki/Bridge
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The beam has to be able to resist the bending which will happen with the biggest load that the designer wants it to take. There are simple examples of stone beam bridges which have survived for a long time. Large modern examples use carefully designed beams to support the bridge deck (the part that we cross over.)
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www.bardaglea.org.uk/bridges/bridge-types/bridge-types-...
www.bardaglea.org.uk/bridges/bridge-types/bridge-types-beam.html
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Over the sturdy beam, there are boards, metal, or most commonly a layer of concrete. The bridge road surface is level with the road, making it very strong. Beam bridges are used to span no more than 250 feet.
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www.pennridge.org/works/brbeam.html
www.pennridge.org/works/brbeam.html
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