Types of Bridges
A bridge is a structure that links two areas together that are divided by some type of obstacle such as water or a steep valley.
Bridges have been built around the world for centuries, with some places still sporting ancient bridges from Roman times.
A bridge can be anything from a plank of wood across a stream to a large concrete construction miles long.
Through the ages bridges have been built from all types of materials from rope, wood, stone, brick, concrete and various metals.
The most common types of bridge come from five general styles of design, they are the arch, the beam,the bascule, the cantilever and the suspension.
THE ARCH BRIDGE
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SYDNEY HARBOUR BRIDGE.
The idea of the arch bridge is to transfer the weight of the bridge outwards towards either side by way of it's curved structure or arch onto it's supporting pillar known as an abutment.An arch bridge can be constructed from one single arch or a series of many arches connected to each other by the abutments.
The most famous of this type of bridge is the Sydney Harbour Bridge in Australia.
This steel arch bridge that spans Port Jackson in Sydney Harbour, carries rail traffic, vehicular traffic, cycles and pedestrians from Millers Point in Sydney's business district to Milsons Point on Sydney's north shore.
Built between 1923 and 1932 the bridge is 3,770 ft ( 1,149m ) in length, 161 ft ( 49m) wide and has a span of 1,650 ft ( 503m). The top of the arch is 439 feet ( 134m) above sea level and the main deck has a clearance of 160 feet ( 49m).
Built as part of the Bradfield Highway transport system the bridge has a variable toll system depending on time of day and time of year.
The longest bridge of this type in the world is the Chautianemen Bridge which spans the River Yangzte in Chongquing, China at 5,712 feet ( 1,741m) long overall with it's main deck 3,057 feet ( 932m) long with a span of 1,811 feet ( 552m), built in 2009.
THE BASCULE OR DRAW BRIDGE.
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The bascule or draw bridge is generally formed from a beam or girder bridge that has been given a deck that can be pulled up to allow traffic to pass under it.
These types of bridges are generally constructed above areas of tidal water where the water level rises and falls quite considerably with the daily tides.
The most famous of this type of bridge is Tower Bridge in London, UK.
Tower Bridge is both a bascule bridge and a suspension bridge that spans the River Thames in London between the borough of Tower Hamlets and the city of London on the north of the river ( Tower of London side) and Bermondsey in the Borough of Southwark on the south side of the river..
The bridge was built between 1886 and 1894 to accomodate two lanes for vehicular traffic and pedestrian walkways .
It's draw bridge section that is positioned in the middle of the river is 196.8 ft ( 60 m) long and allows the passage of tall water craft to pass beneath it and has a 28 ft ( 8.6m) clearance at high tide when closed and due to it's 83 degree raise it can reach a clearence of 139 feet ( 42.5m) when open.
The two stone supporting towers on either side of the draw bridge hold it's 185 feet (56.3m) long suspension platforms - known as piers - and their cables that take the other two sections of the bridge further onto the shore which are further supported by another 40 foot tower ( 12m) . The taller towers are 213 ft ( 64.9m) high and the hydraulic motors housed inside them can lift the draw bridge in less than five minutes.
The upper truss beam at the top of the draw bridge section houses a glassed in walkway for pedestrian traffic.
The longest bridge of this type in the world is the Lake Pontchartrain Causeway bridge between Metaine and Mandeville in Louisiana, USA, which is two parralel road bridges built in 1956 and 1969 respectively which are 24 miles ( 39km) in length.
THE BEAM OR GIRDER BRIDGE.
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THE NITEROI BRIDGE.
The beam or girder bridge is the most simple of the bridge designs and the design that has been around for the longest.
Basically the beam or girder bridge is constructed by way of two or more support pillars which hold up a beam or girder on which the deck - the path, the road or railtrack - is situated on.To make the bridge longer it just requires more support pillars in order to take more beams or girders.
One of the largest types of beam or girder bridge is the President Costa E. Silva Bridge situated over the Guanabara Bay in Rio de Janeiro, Brazil.
Construction began on the 8 lane vehicular traffic bridge in January 1969 and was opened in March 1974.
The bridge is 8.25 miles ( 13km) long and 236.2 feet ( 72 m) wide with a span of 236.2 feet (72 m ).
It is a toll bridge that takes 140,000 vehicles a day between the cities of Rio de Janeiro and Niteroi.
It was named after the president of Brazil at the time of it's construction, President Costa e Silva although it is better known locally as the Niteroi Bridge.
The longest bridge of this type in the world is the Bang Na Expressway in Bangkok, Thailand at 34 miles ( 55km) long by 27 m wide, built in 1996.
THE CANTILEVER BRIDGE.
THE FORTH RAIL BRIDGE.
A cantilever is a projecting beam that is supported at one end and which carries a load at the other end. A cantilevered bridge is formed by two cantilevers being placed next to one another in order for one to counterbalance the other, which are connected by a support pillar. The support pillar is anchored onto a pier at it's base which is buried into the bedrock below.
The most famous of this type of bridge is the Forth Rail Bridge in Scotland that consists of three double cantilevers.
This rail bridge that spans the Firth of Forth waterway between Scotland's capital Edinburgh and the town of Fife is the second longest cantilever bridge in the world and was considered an engineering masterpiece when it was constructed at the end of the 19th century.
Opened in 1890 the bridge is 1.5 miles ( 2.5km) long and has a span of 1,710 ft ( 521.3m) and carries a traffic load of 200 trains a day.
The longest bridge of this type in the world is the Pont de Quebec between the city of Quebec and the town of Levis in Canada at 3,239 feet long ( 987m) by 94 ft ( 29 m) wide with a span of 1,800 ft ( 5,459m ), which was built in 1917.
THE CABLE STAY OR SUSPENSION BRIDGE.
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THE GOLDEN GATE BRIDGE.
The cable stay or suspension bridge are of similar design to one another and are constructed by using cables hung from pillars at either end of the bridge, and it is by way of these cables that the main deck is held aloft. The idea is to form tension in the cable by way of compression from the pillars.The cables are generally made up of multiple steel wires or forged or cast chain links.
This type of bridge is ideal in areas of high wind or unstable ground as the cables allow a certain amount of movement to the structure, enabling it to move ever so slightly at times of high wind or in high risk, earth movement areas.
The most famous of this type of bridge is the Golden Gate Bridge in San Francisco, California, USA.
Built between 1933 and 1937 this six lane, toll, suspension bridge that carries 118,000 vehicles per day between the city of San Francisco and Marin County in California is 8,981 ft ( 1.7km) long and 90 feet (227.4m) wide with a span of 4,200 ft(1,280m).
The bridge was built as part of the highway network U.S Route 101 and California Route 1.
The longest bridge of this type in the world is the Akash Kaikoyo Bridge between Awaji Island and Kobe in Japan at 4 miles long with a span of 1,991 feet, built in 1998.
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