Prikhodko Daria

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Nov 26, 2013 (3 years and 7 months ago)

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Prikhodko Daria

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Elena Aksuta


BRIDGES: CONNECTING HUMANS THROUGH THE AGES

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The essential idea of presented work is to present the main types of bridges,
their constructive specification,
structure and to introduce some of the greatest
construction made by human being for

humanity.

Key words:
bridge, types of bridge, construction.

Can you imagine your life without bridges? Imagine that just a short part of a
distance which connects your hom
e with work, school, city centre, etc has
disappeared for a day. What will you do? I guess nothing. This construction has
appeared when our forefather has begun to transfer trees from the places they had
fallen, to the places where they couldn’t cross the
river by swimming. The first
bridges made by humans were probably spans of cut wooden logs or planks and
eventually stones, using a simple support and crossbeam arrangement. Some early
Americans used trees or bamboo poles to cross small caverns or wells to

get from one
place to another. A common form of lashing sticks, logs, and deciduous branches
together involved the use of long reeds or other harvested fibers woven together to
form a connective rope which was capable of binding and holding in place mater
ials
used in early bridges.

There are six main types of bridges: beam bridges, cantilever bridges, arch
bridges, suspension bridges, cable
-
stayed bridges and truss bridges.



Beam bridges are horizontal beams supported at each end by abutments,
hence their structural name of simply supported. When there is more than one span
the intermediate supports are known as piers. The earliest beam bridges were simple
logs that sat across

streams and similar simple structures. In modern times, beam
bridges are large box steel girder bridges. Weight on top of the beam pushes straight
down on the abutments at either end of the bridge. They are made up mostly of wood
or metal. Beam bridges ty
pically do not exceed 250 feet (76 m) long. The longer the
bridge, the weaker. 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).



Ca
ntilever bridges are built using cantilevers

horizontal beams that are
supported on only one end. Most cantilever bridges use a pair of continuous spans
extending from opposite sides of the supporting piers, meeting at the center of the
obstacle to be cros
sed. Cantilever bridges are constructed using much the same
materials & techniques as beam bridges. The difference comes in the action of the
forces through the bridge. The largest cantilever bridge is the 549
-
metre (1,801 ft)
Quebec Bridge in Quebec, Cana
da.

The bridge accommodates three highway lanes
(none until 1929, one until 1949, two until 1993), one rail line (two until 1949), and a
pedestrian walkway (originally two); at one time it also carried a streetcar line. It has
been owned by the Canadian Na
tional Railway since 1993.



Arch bridges have abutments at each end. Dating to the Greek Bronze
Age the earliest known arch bridges were built by the Greeks and include the
Arkadiko Bridge.

The weight of the bridge is thrust into the abutments at either sid
e.
Dubai in the United Arab Emirates is currently building the Sheikh Rashid bin Saeed
Crossing which is scheduled for completion in 2012. Length of 1.6 kilometers. The
bridge will be 64 meters (210 ft) wide and will rise 15 meters (49 ft) above the water.

When completed, it will be the largest arch bridge in the world.



Suspension bridges are suspended from cables. The earliest suspension
bridges were made of ropes or vines covered with pieces of bamboo. In modern
bridges, the cables hang from towers that a
re attached to caissons or cofferdams. The
caissons or cofferdams are implanted deep into the floor of a lake or river. The
longest suspension bridge in the world is the 12,826 feet (3,909 m) Akashi Kaikyo
Bridge in Japan. The bridge has three spans. The c
entral span is 1,991 m (6,532 ft)[1],
and the two other sections are each 960 m (3,150 ft). The bridge is 3,911 m (12,831
ft) long overall. The central span was originally only 1,990 m (6,529 ft), but the Kobe
earthquake on January 17, 1995, moved the two
towers sufficiently (only the towers
had been erected at the time) so that it had to be increased by 1 m (3.3 ft). The bridge
was designed with a two
-
hinged stiffening girder system, allowing the structure to
withstand winds of 286 kilometers per hour (178

mph), earthquakes measuring to 8.5
on the Richter scale, and harsh sea currents. The bridge also contains pendulums that
are designed to operate at the resonance frequency of the bridge to damp forces. The
two main supporting towers rise 298 m (978 ft) ab
ove sea level, and the bridge can
expand because of heating up to 2 meters (7 ft) over the course of a day. Each
anchorage required 350,000 tones (340,000 LT; 390,000 ST) of concrete. The steel
cables have 300,000 kilometers (190,000 mi) of wire: each cabl
e is 112 centimeters
(44 in) in diameter and contains 36,830 strands of wire. The Akashi
-
Kaikyo bridge
has a total of 1737 illumination lights: 1084 for the main cables, 116 for the main
towers, 405 for the girders and 132 for the anchorages. On the main c
ables three high
light discharged tubes are mounted in the colors red, green and blue. The RGB model
and computer technology make for a variety of combinations. Currently, 28 patterns
are used for occasions as national or regional holidays, memorial days o
r festivities



Cable
-
stayed bridges, like suspension bridges, are held up by cables.
However, in a cable
-
stayed bridge, less cable is required and the towers holding the
cables are proportionately shorter. The first known cable
-
stayed bridge was designed
in

1784 by C.T. Loescher. The longest cable
-
stayed bridge is the Sutong Bridge over
the Yangtze River in China.

With a span of 1,088 meters (3,570 ft), it is the cable
-
stayed bridge with the longest main span in the world as of 2010. Its two side spans
are 3
00 meters (980 ft) each, and there are also four small cable spans. Two towers of
the bridge are 306 meters (1,004 ft) high and thus the second tallest in the world. The
total bridge length is 8,206 meters (26,923 ft)



Movable bridges are designed to move o
ut of the way of boats or other
kinds of traffic, which would otherwise be too tall to fit. These are generally
electrically powered. Tower Bridge is well known all over the world. This bridge is
rich in innovation engineering solutions. The main problem w
as a creation of turning
machinery reliable in service. There was installed a compound hydraulic system
which is still working.

In
the conclusion it could be said that bridges unite what was divided by
nature. Some of them are masterpieces of architecture. On the one hand there are
difficult structures and difficult materials which are used building bridges, on the
other hand


light
composition which could make us believe that it could be air
bridge.

REFERENCES:

1.

The most beautiful bridges in the world

http://www.nice
-
places.com/articles/europe/different/335
.htm

2.

Bridges
http://en.wikipedia.org/

3.

All about bridges
http://www.am
-
bridge.net/bridge/

4.

“100 чудес современной архитектуры” Элисон Ахерн 2006

5.

“Masterpieces: bridge
architecture + design” Brown 2009