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Beam bridges are very easy to build and consist of a flat horizontal slab that lays atop two vertical supports at either end

Simple beam bridges do not measure longer than 250 feet.

Beam bridges can be connected over longer distances on multiple supports to form continuous span bridges.

The longest bridge in the world is a continuous span bridge called the Lake Ponchartrain Causeway. It is located in Louisiana. It spans about 24 miles.

The primary building materials for highway beam bridges are steel and concrete.

When weight is added to a traditional beam bridge, it bends in the middle.

Sources: Encyclopeida.com, Encyclopedia Brittanica
Image source: CNN/David Fraser

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Arch bridges were developed by the ancient Romans and are still in use today

Arch bridges were first built with stone and brick, but are now mainly built using steel and concrete

Arch bridges work by distributing weight across a curved arch and onto two abutments on either end.

Pictured below is Pont Valentré in Cahors, France. It was finished in 1380 after 70 years of construction. It has eight arches and is registered as a UNESCO world Heritage site as part of the pilgrimage routes of Santiago de Compostela

Sources: Design-technology.org, Encyclopedia Brittanica, holidays-cahors.co.uk, UNESCO
Image source: Pixabay

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Suspension bridges can be very expensive. The Guinness World record for most expensive bridge is held by California's Bay Bridge (pictured below). It cost $6.3 billion to reconstruct  in 2002 after an earthquake destroyed sections in 1989.

Suspension bridges are made of two (or more) vertical towers and two long horizontal cables that rise along the sides of the bridge and fall into an inverted arch between the towers. Numerous short vertical cables known as suspenders connect the horizontal cables to the roadway. Most of the weight on the bridge is supported by the two towers.

The horizontal cables are secured on either end of the bridge by rock or concrete anchorages, which pull outward on the towers with equal force as the road pulls inward on the towers, balancing out the force.

The Golden Gate Bridge is the most well-known suspension bridge in the world. Other famous suspension bridges include Tower Bridge in London, the Brooklyn Bridge in New York, and the Akashi-Kaikyo Bridge in Kobe, Japan, the longest suspension bridge ever built.

The Golden Gate bridge also incorporates trusses and arches in its construction

Sources: PBS, Wonderopolis, Guinness World Records
Image source: thepolisblog.org

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Truss bridges are supported by a series of "trusses" which are triangular structures that are very stable

There are more variations in truss bridges than in the other main bridge types, and many of the other types incorporate trusses in their design

The trusses can be found underneath the roadbed (deck truss) , supporting it on either side (pony truss) , or on the sides and top (through truss). There are lots of other variations that include the other types of bridges.

Pictured below is the Tokyo Gate Bridge in Japan. It is nicknamed the Dinosaur bridge because its truss structures look like two dinosaurs facing each other.

Sources: Encyclopedia Brittanica, North Carolina Department of Transportation
Image source: Zengame/wikimedia.org