Presentation about bridges, Slides of English Language

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Bridges

Basic forms There are six basic bridge forms:

• (^) the beam,
• (^) the truss
• (^) the arch
• (^) the suspension
• (^) the cantilever
• (^) and the cable-stay. Bridge, structure that spans horizontally between supports, whose function is to carry vertical loads. The prototypical bridge is quite simple two supports holding up a beam yet the engineering problems that must be overcome even in this simple form are inherent in every bridge: the supports must be strong enough to hold the structure up, and the span between supports must be strong enough to carry the loads.

Beam

The beam bridge is the most common bridge form. A beam carries vertical loads by bending. As the beam bridge bends, it undergoes horizontal compression on the top. At the same time, the bottom of the beam is subjected to horizontal tension. The supports carry the loads from the beam by compression vertically to the foundations. Truss A single-span truss bridge is like a simply supported beam because it carries vertical loads by bending. Bending leads to compression in the top chords (or horizontal members), tension in the bottom chords, and either tension or compression in the vertical and diagonal members, depending on their orientation. Trusses are popular because they use a relatively small amount of material to carry relatively large loads.

The arch bridge carries loads primarily by compression, which exerts on the foundation both vertical and horizontal forces. Arch foundations must therefore prevent both vertical settling and horizontal sliding. In spite of the more complicated foundation design, the structure itself normally requires less material than a beam bridge of the same span. Arch

Suspension

A suspension bridge carries vertical loads through curved cables in tension. These loads are transferred both to the towers, which carry them by vertical compression to the ground, and to the anchorages, which must resist the inward and sometimes vertical pull of the cables. The suspension bridge can be viewed as an upside-down arch in tension with only the towers in compression. Because the deck is hung in the air, care must be taken to ensure that it does not move excessively under loading. The deck therefore must be either heavy or stiff or both.

Materials The four primary materials used for bridges have been wood, stone, iron, and concrete. Of these, iron has had the greatest effect on modern bridges. From iron, steel is made, and steel is used to make reinforced and prestressed concrete. Modern bridges are almost exclusively built with steel, reinforced concrete, and prestressed concrete. Bridges are designed, first, to carry their own permanent weight, or dead load; second, to carry traffic, or live loads; and, finally, to resist natural forces such as winds or earthquakes.

A beam bridge is supported by one or more beams. An example of a beam bridge is southern Louisiana's Lake Pontchartrain Causeway bridge that spans 23.83 miles. It is the world's longest. A truss bridge is supported by a truss that bears the load of the bridge and everything that crosses it. A cantilever bridge is built with two sections that are each supported on one side and meet in the middle. The largest cantilever bridge in the world is the Quebec Bridge in Canada, at 1801 feet. The world's oldest bridge still being used is the stone-segment arched Zhaozhou Bridge in China that was built in 605 A.D. The Inca civilization in South America is known for the rope suspension bridges they built to enable crossing steep ravines and gorges in the jungle. The Akashi Kaikyo Bridge in Kobe, Japan spans a distance of 6529 feet. When it opened for use in 1998 it became the longest suspension bridge in the world. The busiest bridge is the George Washington Bridge that connects New Jersey's Bergen County to New York City. More than 102 million vehicles use it each year. It is a double decker bridge. The Golden Gate Bridge in San Francisco is 8981 feet long and incorporates 80,000 miles of cable. It is one of the most famous bridges in the world. Interesting facts about bridges

Technical words

1. prototypical bridge –прототип моста прототип моста
2. spans - пролеты
3. single-span truss bridge -однопролетный ферменный мост
4. undergoes horizontal compression -подвергается горизонтальному сжатию
5. anchorages -якорные стоянки
6. deck- колода
7. horizontal sliding -горизонтальное скольжение
8. upside-down arch -перевернутая арка
9. cantilevered -консольный
10. Inner towers –прототип моста внутренние башни
11. straight diagonal cables -прямые диагональные кабели
12. rope suspension bridges -канатные подвесные мосты
13. stone-segment arched -каменно-сегментный арочный
14. steep ravines -крутые овраги
15. gorges -ущелья
16. suspension bridge -подвесной мост
17. Cable-stayed bridges -вантовые мосты
18. dead load -статическая нагрузка
19. prestressed concrete- предварительно напряженный бетон
20. supports holding -поддерживает удержание