Bridges
Introduction
History of Bridges
Types of Bridges
Examples and Reasons for Collapse of Bridges
Famous Bridges in Alberta
Conclusion

Introduction:

A bridge is a structure that allows people and vehicles to cross over an open space. Bridges have always been and will be required for the development of trade, transport, travel and just for communication between people. We are going to present the history of bridge building, information about different types of bridges, the facts and causes of bridge collapse and some famous bridges in Alberta.

History of Bridges:

Thousands years ago, people start to put trees or stones to connect two sides of a river to pass across. That was the simple way to build a Bridge. The first known bridges were in Greece, but Ancient Romans were the greatest builders with the Arch type of bridges. Many of old bridges were collapsed because of floods. However, the bases to construct a bridge were improved during time to build strong, long, resistant bridges to be used in multiple ways.

Types of Bridges:

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  • Beam bridges: are made from horizontal long thick piece of wood or metal that supported at each end by masonry support that touches and directly receives the pressure. They do not exceed 250 feet (76 m) long. The world's longest beam bridge is Lake Pontchartrain Causeway in southern Louisiana in the United States, at 23.83 miles (38.35 km), with individual spans of 56 feet (17 m).






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  • Cantilever bridges: are made using wood or metal, built using cantilevers (horizontal beams supported on only one end). Most cantilever bridges use a pair of continuous spans that extend from opposite sides of the supporting piers to meet at the center of the obstacle the bridge crosses. The largest cantilever bridge is the 549-metre (1,801 ft) Quebec Bridge in Quebec, Canada.













  • 1244739801.jpgArch bridges: are built from stones or concrete, have axes (masonry support that touches and directly receives thrust or pressure) at each end. The largest arch bridge will be completed in 2012 in Dubai, it named "Sheikh Rashid bin Saeed Crossing"
    The example of an ancient arch bridge is one of the Roman bridges on Afrin river in Syria.
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  • Suspension bridges: are built from cables that attached to large watertight chamber used for construction under water. The longest suspension bridge in the world is the 12,826 feet (3,909 m) Akashi Kaikyo Bridge in Japan.









  • 800px-Sutong_Bridge.jpgCable-stayed bridges: are designed as suspension bridges but it requires less cable and the towers that hold the cables are shorter. The longest cable-stayed bridge is the Sutong Bridge over the Yangtze River in China.







  • 120px-MovableBridge_curl.gifMovable bridges: are designed to open to facilitate the passage of boats or ships in the river. Generally, they are powered by electricity.













  • 800px-Craigavon_bridge.jpgTruss bridges: are designed to with two levels (upper one and lower one) to use the bridges for more than one purpose level for vehicles and level for railways or pedestrians.










Examples and Reasons for Collapse of Bridges:

The physical phenomenon of resonance occasionally causes a bridge to collapse.
Broughton Bridge was one of the first suspension bridges constructed in Europe. It was built in 1826 in England. The bridge collapsed in 1831. Soldiers were marching over the bridge in step and the bridge began to vibrate. The vibration increased rapidly and one of the iron columns supporting the suspension chains fell towards the bridge. About forty people were throwing in the water. Fortunately, nobody was killed as the water was only about two feet deep. After that was issued an order that troops should "break step" when crossing a bridge.

A similar incident occurred in France in 1850. Angers Bridge, also called the Basse-Chaîne Bridge, was a suspension bridge. The battalion used the bridge during a powerful thunderstorm when the wind was making the bridge oscillate. The soldiers had been ordered to break step. However, their efforts to match the swaying and keep their balance may have caused them to involuntarily contributing to the resonance. In any case, the oscillation increased, the cable broke and the bridge collapsed. Over 200 people died. It is the greatest number of casualties in bridges’ collapse.
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Tacoma Narrows Bridge: The dramatic, rhythmic twisting that resulted in the 1940 collapse of the original Tacoma Narrows Bridge, is characterized in physics textbooks as a example of resonance. At the time of its construction (and its destruction), the bridge was the third longest suspension bridge in the world.



The failure of bridge happened as a result of mechanical resonance. The bridge started to move up and down more and more rapidly. This motion is generally called oscillation. When size of the oscillations got so large, the bridge broke because it had been constructed improperly. Resonance requires three basic conditions:
  1. An object with a natural frequency (When we are standing on the big bridge, we sometime feel the vibration)
  2. A forcing function at the same frequency as the natural frequency (It may be steps or wind)
  3. A lack of damping or energy loss (Damping is a means of removing mechanical energy by converting it to heat)
When the forcing function's frequency matches the natural frequency of an object it will begin to resonate. It means the oscillation's amplitude grow larger and larger. Before the oscillations reach infinity one of three things happens:
1) the object's dynamics change so that the resonant frequency and forcing functions no longer match
2) the energy lost or
3) the object breaks

Famous Bridges in Alberta

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High Level Bridge - Lethbridge
The impressive High Level Bridge is located 257km southeast from Calgary. This Canadian Pacific railway single-track viaduct, built between 1907 and 1909 across the Oldman River Valley, was an engineering triumph. It the longest and highest trestle steel bridge in Canada reaching 1.600 meters in length and 95 meters in height. By allowing significantly longer trains shorter transit times, the Lethbridge viaduct greatly increased capacity of the Crowsnest Pass Route.




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The Centre Street Bridge across the Bow River, Calgary, was built in 1916. The remarkable feature of the bridge is the four massive concrete lions. The bridge went through extensive restoration in 2001 and the original lions were replaced. One of the original lions is now located at City Hall.
Now this bridge is the truss one - its low level is shorter than upper and connects just the shores of the river.



Conclusion:
The bridges have a long history, different design and made from different materials. The engineers improve the technology constantly to build high, long and resistant bridges. Alberta has many beautiful bridges that we invite you to discover.

Bibliolgraphy:


History and Types of Bridges
Roman Bridges
The Sheikh Rashid bin Saeed Crossing
Angers Bridge - France
Tacoma Narrows Bridge
Mechanical Resonance
High Level Bridge - Lethbridge, Alberta
Central Street Bridge (Calgary)
Lake Pontchartrain Causeway-Flicker
Akashi Kaikyo Bridge
Sutong Bridge
Movable bridges
High Level Bridge - Lethbridge (from Irina's camera)