is a structure built to span
a valley, road, body of water, or
other physical obstacle, for the purpose of providing passage over
the obstacle. Designs of bridges vary depending on the function of
the bridge and the nature of the terrain where the bridge is
The first bridges were made by nature — as simple as a log fallen
across a stream. The first bridges made by humans were probably
spans of 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.
literature of India provides
mythological accounts of bridges constructed from India to Lanka by the army of Rama.
mentions the construction of dams and
bridges. A Mauryan
bridge near Girnar
was surveyed by James Princep. The bridge was
swept away during a flood, and later repaired by Puspagupta, the
chief architect of emperor Chandragupta
. The bridge also fell under the care of the Yavana
Tushaspa, and the Satrap
Rudra Daman. The use of stronger bridges using plaited bamboo and
iron chain was visible in India by about the 4th century. A number
of bridges, both for military and commercial purposes, were
constructed by the Mughal
administration in India.
The greatest bridge builders of antiquity were the ancient Romans
. The Romans built arch bridges
that could stand in conditions that would
damage or destroy earlier designs. Some stand today. An example is the
Bridge, built over the river Tagus, in Spain.
Romans also used cement, which reduced the variation of strength
found in natural stone. One type of cement, called pozzolana
, consisted of water, lime, sand, and
bridges were built after the Roman era, as the technology for
cement was lost then later rediscovered.
large Chinese bridges of wooden construction existed at the time of
the Warring States, the oldest
surviving stone bridge in China is the Zhaozhou Bridge, built from 595 to 605 AD during the Sui Dynasty.
This bridge is also
historically significant as it is the world's oldest open-spandrel
stone segmental arch bridge. European segmental
arch bridges date back to at least the Alconétar
Bridge (approximately 2nd century AD), while the enormous
Roman era Trajan's
Bridge (105 AD) featured open-spandrel segmental arches in
, a simple type of
suspension bridge, were used by the Inca
civilization in the Andes
mountains of South
America, just prior to European colonization in the 1500s.
During the 18th century there were many innovations in the design
of timber bridges by Hans Ulrich
, and others.
The first book on bridge engineering was written by Hubert Gautier
in 1716. A major breakthrough
in bridge technology came with the erection of the The Iron Bridge in Coalbrookdale, England in 1779.
It used cast iron
for the first time as arches to cross
the river Severn
With the Industrial Revolution
in the 19th century, truss
systems of wrought iron
were developed for larger bridges,
but iron did not have the tensile
to support large loads. With the advent of steel,
which has a high tensile strength, much larger bridges were built,
many using the ideas of Gustave
welding pioneer Stefan Bryła designed the first
welded road bridge in the world who was later built across the
river Słudwia Maurzyce near
Poland in 1929.
In 1995, the American Welding Society
an Historic Welded Structure Award for the bridge to Poland.
The Oxford English Dictionary traces the origin of the word
to an Old English word brycg
, of the same
meaning, derived from a hypothetical Proto-Germanic
in other Germanic languages
(for instance Brücke
in Dutch, brú
Norwegian and Swedish).
Types of bridges
There are six main types of bridges: beam
, cantilever bridges
, suspension bridges
, cable-stayed bridges
and truss bridges
Beam bridges are horizontal beams supported at each end by 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 piers at either end of the bridge. They are made up mostly of wood or metal.
using cantilevers—horizontal beams that are supported on only one
end. Most cantilever bridges use two cantilever arms extending from
opposite sides of the obstacle to be crossed, meeting at the
center. The largest cantilever bridge is the Quebec Bridge in Quebec, Canada.
and have abutments at each end. 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
either side. Dubai in the
Emirates is currently building the Sheikh Rashid
bin Saeed Crossing which is scheduled for completion in 2012.
When completed, it will be the largest arch bridge in the
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 are 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 Akashi Kaikyo
Bridge in Japan.
See simple suspension bridge
, stressed ribbon bridge
, underspanned suspension
, suspended-deck suspension
, and self-anchored suspension
Like suspension bridges, cable-stayed 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
Bridge over the Yangtze River in China.
Continuous under-deck truss
Over-deck truss bridge with steel
girders and wooden carriageway
are composed of connected
elements. They have a solid deck and a lattice of pin-jointed or
gusset-joined girders for the sides. Early truss bridges were made
of wood, and later of wood with iron tensile rods, but modern truss
bridges are made completely of metals such as wrought iron and
steel or sometimes of reinforced concrete. The Quebec Bridge, mentioned above as a cantilever bridge, is also
the world's longest truss bridge.
A bridge is designed for trains, pedestrian or road traffic, a
pipeline or waterway for water transport or barge traffic. An
is a bridge that carries water,
resembling a viaduct
, which is a bridge that
connects points of equal height.A road-rail bridge carries both
road and rail traffic.
Bridges are subject to unplanned uses as well. The areas underneath
some bridges have become makeshift shelters and homes to homeless
people, and the undersides of bridges all around the world are
spots of prevalent graffiti. Some bridges attract people attempting
, and become known as suicide bridges
To create a beautiful image, some bridges are built much taller
than necessary. This type, often found in east-Asian style gardens,
is called a Moon bridge
, evoking a
rising full moon. Other garden bridges may cross only a dry bed of
stream washed pebbles, intended only to convey an impression of a
stream. Often in palaces a bridge will be built over an artificial
waterway as symbolic of a passage to an important place or state of
set of five bridges cross a sinuous waterway in an important
courtyard of the Forbidden
City in Beijing, the People's
Republic of China.
The central bridge was reserved exclusively
for the use of the Emperor, Empress, and their attendants.
Differences and similarities in bridge structure
A bridge taxonomy showing evolutionary
Bridges may be classified by how the forces of tension
are distributed through their structure.
Most bridges will employ all of the principal forces to some
degree, but only a few will predominate. The separation of forces
may be quite clear. In a suspension or cable-stayed span, the
elements in tension are distinct in shape and placement. In other
cases the forces may be distributed among a large number of
members, as in a truss, or not clearly discernible to a casual
observer as in a box beam. Bridges can also be classified by their
lineage, which is shown as the vertical axis on the diagram to the
A bridge's structural efficiency
may be considered to be
the ratio of load carried to bridge mass, given a specific set of
material types. In one common challenge students are divided into
groups and given a quantity of wood sticks, a distance to span, and
glue, and then asked to construct a bridge that will be tested to
destruction by the progressive addition of load at the center of
the span. The bridge taking the greatest load is by this test the
most structurally efficient
. A more refined measure for
this exercise is to weigh the completed bridge rather than measure
against a fixed quantity of materials provided and determine the
multiple of this weight that the bridge can carry, a test that
emphasizes economy of materials and efficient glue joints (see
balsa wood bridge
A bridge's economic efficiency
will be site and traffic
dependent, the ratio of savings by having a bridge (instead of, for
example, a ferry, or a longer road route) compared to its cost. The
lifetime cost is composed of materials, labor, machinery,
engineering, cost of money, insurance, maintenance, refurbishment,
and ultimately, demolition and associated disposal, recycling, and
replacement, less the value of scrap and reuse of components.
Bridges employing only compression are relatively inefficient
structurally, but may be highly cost efficient where suitable
materials are available near the site and the cost of labor is low.
For medium spans, trusses or box beams are usually most economical,
while in some cases, the appearance of the bridge may be more
important than its cost efficiency. The longest spans usually
require suspension bridges.
Double-decker bridges have two levels, such
as the San Francisco – Oakland Bay
Bridge, with two road levels. Tsing Ma
Bridge and Kap Shui Mun Bridge in Hong
Kong have six lanes on their upper decks, and on their
lower decks there are two lanes and a pair of tracks for MTR metro trains. Likewise, in Toronto, the Prince Edward Viaduct has four lanes of motor traffic on its upper deck
and a pair of tracks for the Bloor–Danforth subway line. Some double-decker
bridges only use one level for street traffic; the Washington Avenue Bridge in Minneapolis reserves its lower level for automobile traffic and
its upper level for pedestrian and bicycle traffic (predominantly
students at the University of Minnesota).
Robert Stephenson's High Level
Bridge across the River Tyne in
upon Tyne, completed in 1849, is an early example of a
The upper level carries a railway, and
the lower level is used for road traffic.
example is Craigavon
Bridge in Derry, Northern
Ireland. The Oresund Bridge between Copenhagen and Malmö consists of
a four-lane highway on the upper level and a pair of railway tracks
at the lower level.
Washington Bridge between New Jersey and New York has two roadway
It was built with only the upper roadway as traffic
demands did not require more capacity. A truss
work between the roadway levels provides stiffness to the roadways
and reduced movement of the upper level when installed.
Tower Bridge is different example of a double-decker bridge,
with the central section consisting of a low level bascule span and a high level footbridge.
More than just a bridge
bridges carry special installations such as the tower of Nový
Most bridge in Bratislava which carries a restaurant. Other suspension
bridge towers carry transmission antennas.
- Costs and cost overruns in bridge
construction have been studied by Flyvbjerg et al. (2003). The
average cost overrun in building a bridge was found to be 34%.
- In railway parlance, an overbridge is
a bridge crossing over the course of the railway. In
contrast, an underbridge allows passage
under the line.
The failure of bridges is of special concern for structural engineers
in trying to learn
lessons vital to bridge design, construction and maintenance. The
failure of bridges first assumed national interest during the
when many new designs
were being built, often using new materials.
Some bridges are not fixed crossings, but can move out of the way
of boats or other kinds of traffic which, ideally, moves under
them, but is sometimes too tall to fit.
Index to types
Double Blind Arcade
File:Nagasaki Meganebashi M5257.jpg|
Image:Concrete box girder bridge.JPG|
Box girder bridge
Image:Puente del Alamillo.jpg|
spar cable-stayed bridge
Image:Tarr Steps 01.jpg|
Image:Vallorcine footpath bridge 2003-12-13.jpg|
Image:Salmon Bay Bridge-2Clip.jpg|
Image:Pigtail Bridge on US 16A.jpg|
Image:Pontoon bridge Rhine River 1945.jpg|
Image:Holzbrücke bei Essing 1.jpg|
Truss arch bridge
Image:Conwy Castle 2.jpg|
- Roman Bridge in Cordoba ( 1st century
- Kinney, pg. 190
- Buck pg 78
- Dikshitar, pg. 332
- Dutt, pg 46
- "suspension bridge" in Encyclopaedia Britannica (2008). 2008
Encyclopedia Britannica, Inc.
- Nath, pg. 213
- Context for World Heritage Bridges
- History of BRIDGES
- Lessons from Roman Cement and Concrete
- World's Longest Bridge Spans
- Flyvbjerg, Bent, Nils Bruzelius, and Werner
Rothengatter, 2003. Megaprojects and Risk: An Anatomy of
Ambition (Cambridge: Cambridge University Press).
- Brown, David J. Bridges: Three Thousand Years of
Defying Nature. Richmond Hill, Ont: Firefly Books, 2005. ISBN
- Sandak, Cass R. Bridges. An Easy-read modern
wonders book. New York: F. Watts, 1983. ISBN
- Whitney, Charles S. Bridges of the World: Their
Design and Construction. Mineola, NY: Dover Publications,
2003. ISBN 0-486-42995-4.
- Unabridged republication of Bridges : a study in
their art, science, and evolution. 1929.
- Dikshitar, V. R. R. Dikshitar (1993). The Mauryan
Polity. Motilal Banarsidass. ISBN 8120810236.
- Dutt, Romesh Chunder (2000). A History of
Civilisation in Ancient India: Vol II. Routledge. ISBN
- Nath, R. (1982). History of Mughal
Architecture. Abhinav Publications. ISBN
- Kinney, A. R.; el al. (2003). Worshiping Siva and
Buddha: The Temple Art of East Java. University of Hawaii
Press. ISBN 0824827791.
- Buck, William; el al. (2000). Ramayana.
University of California Press. ISBN 0520227034