Bridges , livre ebook

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ISBN: 978-1-78525-922-7
B RIDGES
Contents


Introduction
I. Stone and Brick
II. Wood
III. Metal
Concrete
Index
Suspended Bridge
Location : Mustang, Annapurna, Nepal
Material : Steel


Introduction


The urban and rural landscapes of today are marked with many structures that are frequently overlooked because of their habitual use. Bridges are examples of such structures. Do residents of San Francisco often fall into raptures over the remarkable Golden Gate Bridge, Parisians over the Pont Alexandre III or Londoners over the Tower Bridge? In fact, bridges’ aesthetic qualities and often the impressive technological prowess that contributed to their creation deserve an admiring pause: bridges are in essence dynamic sculptures, inhabiting the landscape, marking society’s development throughout history. These structures made of wood, stone or iron represent the means of physical communication, from railroads to interstate highways, that connect our villages, our cities, our provinces, our countries. Soaring over streams and rivers, overcoming ravines and linking continents, bridges are essential to civilisation and unifying tools for society. These masterpieces of architecture rise above mere utility and become the simultaneous expressions of our history and our future.
Was the first bridge perhaps an accident of nature? Most likely a fallen tree landed across the banks of a river, connecting the opposite sides. Before man learned of the advantage of crossing bodies of water without getting wet, animals undoubtedly borrowed this new route. Imitating this original natural bridge, so rudimentary at first glance, man discovered that it was possible to make the passages more sophisticated, endowing bridges with strength and durability.
As civilisations developed and progressed, bridges were constructed with finely-worked wood and stones were used to reinforce their foundations. Earlier than the third millennium B.C.E., frescoes and texts refer to the construction of bridges in association with the names of monarchs, who used the structures as demonstrations of their power and endurance. Two bridges have found permanent places in history: that of Egyptian pharaoh Menes, constructed around 2560 B.C.E. across the Nile, and that of Assyrian Queen Semiramis, built over the River Euphrates several centuries later.
With the barbarian invasions of the 5th and 6th centuries C.E., Roman lines were pushed back by marauding groups from the East. Visigoths, Franks, Huns and Vandals surged through the civilised world, leaving ruined cities, roads and bridges in the wake of their violence.
Stability was restored to Europe in the 7th century. In the late 8th century, Charlemagne reassembled lands into a unified territory and, feeling the need for rapid movement of troops, began to improve the paths of communication in the heart of Europe. The renovation efforts, while modest, were put into effect, and soon various construction methods were discovered or rediscovered.
The Middle Ages saw marked progress under pressure from merchants who were developing their business enterprises beyond the limits of their hometowns. Bridges were once again in demand, old remnants restored and new bridges appearing at strategic locations over streams and rivers.
During the Renaissance, bridges became indispensable to commerce and warring armies throughout Europe. Adding to their utilitarian qualities, bridges were endowed with importance by princes, who wished to impress their contemporaries and demonstrate their prestige by leaving lasting monuments like bridges in their respective cities. Bridges were erected thus in Florence, Venice, Paris and London, often housing shops or residences. The development of tolls as a way of taxing goods or people crossing the waterways further increased the popularity of bridges during the Renaissance. Thanks to the cultural rebirth and scientific innovations of this period, people were able to build longer, more artistically complex bridges. In 1747, under the supervision of Louis XV, France became the first country to establish a specialised school for urban engineering: the École Royale des Ponts et Chaussées.
Throughout the 18th and 19th centuries, construction techniques advanced at an incredible pace with new discoveries. Wood and stone, which had remained the materials of choice for bridge-building, were being replaced by the stronger, more practical substances bronze, iron and steel. Engineers, no longer timid or restrained by technological limitations, spanned every stream and river in the western world with a bridge, permitting, at the same time, the development of railroads.
As countries, cities and towns were thus connected by new means of communication and as trains became heavier and longer, further innovations in the construction of bridges became necessary. In addition to improving the technical properties of these passageways, engineers like Gustave Eiffel, with his Garabis viaduct, built in 1882, used metal and its capabilities to raise the aesthetic value of bridges to the level of architectural monuments, testifying to the triumphant 19th century. Furthermore, with Europe’s colonisation of Asia and Africa, the entire world was being transformed into wide streets, bridges and other ingenious roadways.
The 20th century was the century of the automobile, large roads and highways, continuing to serve millions of people. The bridges built in modern times are taller, wider and constantly more numerous; nothing seems to stand in the way of engineers, no ravine, stream or river is too deep or wide or wild to be spanned.
However, even in the midst of this frenetic industrial pace, many bridges created in the past have today become symbols rather than structures, like the ‘bridge on the River Kwai’, immortal testimonials to our collective history.
Bogdan Khmelnitsky (Kievsky) Pedestrian Bridge
Location : Moscow, Russia. Crosses : Moskva River
Material and type : Arch bridge, two hinged
Completed : 2 September 2001
Alcántara Bridge
Location : Alcántara, Extremadura, Spain
Crosses : Tagus River. Architect : Gaius Julius Lacer
Material and type : Arch bridge, opus quadratum (stone)
Dimensions : length: 194 m, width: 8 m, height: 71 m, arches: 6
Construction : c. 104-106 C.E.


I. Stone and Brick


Because of the durability of the materials, the oldest bridges still standing today were generally made from stone or brick. Earlier than 200 B.C.E., Greek and Etruscan architects, who had been summoned to construct the bridges of Ancient Rome, built segmented, semicircular arches to support the initial structures. This technique allowed the construction of much longer bridges, while strengthening the structure and permitting a less-obstructed flow of water below the passage in the event of a flood. Most Roman bridges, particularly aqueducts, were built based on this principle of multiple arches.
At the end of the 18th and beginning of the 19th century, engineers like Thomas Telford, Isambard Kingdom Brunel and John Rennie continued to use arches of cut stone or brick in their modern bridges for the durability of the materials as well as their beauty and ability to blend in harmoniously with the surrounding landscape.
Pont-du-Gard
Location : near Nîmes, Languedoc-Roussillon, France. Crosses : Gardon River
Material and type : Arch bridge, stone, used as aqueduct, then road bridge, finally tourist attraction
Dimensions : length: 275 m, long span: 25.3 m, height: 47.7 m, width of channel: 1.2 m; slope: 0.19 m/km
Construction : 19 B.C.E.


The Pont-du-Gard is a Roman aqueduct that was constructed during the reign of Caesar Augustus in 19 B.C.E. Composed of three layers of arches, it has a total height of about 48 metres and measures 275 metres in length. It was intended to transport water from sources of the Eure and Airan rivers, near the town of Uzès, to the city of Nîmes. A masterpiece of Roman engineering, the bridge was constructed of cut stones, using neither mortar nor cement. The water pipe, so to speak, measures 1.2 metres wide and 1.6 metres high. The aqueduct crosses the river Gardon, situated at the bottom of a deep valley, and the principle arch that spans the river has an opening of 25.3 metres.
Pont Saint-Bénezet, also known as Pont d’Avignon
Location : Avignon, Provence-Alpes-Côte d’Azur, France. Crosses : Rhone River
Material and type : Fixed arch bridge, stone, road bridge
Dimensions : spans: 20, measuring 30.8 to 33.5 m each, total length: 900 m
Construction : 1171-1186, disused in 1680


Construction of the Pont Saint-Bénezet, better known as the Pont d’Avignon thanks to the popular song “Sur le Pont d’Avignon”, took place in the 12th century. Tradition attributes the idea for the bridge to a young shepherd named Bénezet, who has been considered a ‘saint’ since the 13th century, although he has never been officially canonised, contrary to the common belief that his canonisation indeed took place under Pope Innocent IV.
Of the nineteen arches that originally formed the bridge, unfortunately only four survive today, creating a particularly bold and picturesque impression. The elegant, exceptional chapel, built at the same time as the bridge between the third arch and the fo