Bridge

The longest spans usually require suspension bridges. It is used for screws and wires. 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. It is somewhat stronger than copper and it has equivalent ductility. Bridges employing only compression are relatively inefficient structurally, but may be highly cost efficient where suitable materials are available near the site. Commercial bronze is 90% copper and 10% tin. For a given site, kind of bridge employed and the materials used determine the total cost, a lifetime cost composed of materials, labor, machinery, engineering, cost of money, maintenance, refurbishment, risk potential, and ultimately, demolition and associated disposal, recycling, and reuse. Alpha bronze alloys of 4-5% tin are used to make coins, springs, turbines and blades.

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. Alpha bronze consists of the alpha solid solution of tin in copper. A more refined measure for this exercise is to weigh the completed bridge rather than measure against a fixed quantity of materials provided, a test that emphasizes economy of materials and efficient glue joints. Bronze is typically 60% copper and 40% tin. The bridge taking the greatest load is by this test the most structurally efficient. Phosphor bronze is particularly suited to precision-grade bearings and springs. In one common challenge young students are to be divided into groups of two or three and then to be given a fixed quantity of wood sticks, a specific distance to span, and a given glue, and then to construct a bridge that will be tested to destruction by the progressive addition of load at the center of the span. Bronze is still widely used today for springs, bearings, bushings and similar roles, and is particularly common in the bearings on small electric motors.

A bridge's structural efficiency may be considered to be the ratio of load carried to bridge weight, given a specific set of material types. Bronze also has very little metal-on-metal friction, which made it invaluable for the building of cannon where iron cannonballs would otherwise stick in the barrel. Bridges can also be classified by their lineage, which is shown as the vertical axis on the diagram to the right. Common bronze alloys often have the unusual and very desirable property of expanding slightly just before they set, thus filling in the finest details of a mould. 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. Bronze is the most popular metal for top-quality bells and cymbals, and also for cast metal sculpture (see bronze sculpture). The separation of forces may be quite clear, as in a suspension or cable-stayed span; the elements in tension are distinct in shape and placement. Aluminium is also used for the structural metal Aluminium bronze.

Most bridges will employ all of the principle forces to some degree, but only a few will predominate. In the twentieth century, silicon was introduced as the primary alloying element, creating an alloy with wide application in industry and the major form used in contemporary statuary. Bridges may be classified by how the four forces of tension, compression, bending and shear are distributed through their structure. Some common examples are the high electrical conductivity of pure copper, the excellent deep-drawing qualities of cartridge case brass, the low-friction properties of bearing bronze, the resonant qualities of bell bronze, and the resistance to corrosion by sea water by several bronze alloys. The central bridge was reserved exclusively for the use of the Emperor, Empress, and their attendants. Copper and its alloys have a huge variety of uses that reflect their versatile physical, mechanical, and chemical properties. A set of five bridges cross a sinuous waterway in an important courtyard of the Forbidden City in Beijing, China. The cost of copper-base alloys is generally higher than that of steels but lower than that of nickel-base alloys.

Often in palaces a bridge will be built over an artificial waterway as symbolic of a passage to an important place or state of mind. Bronzes also conduct heat and electricity better than most steels. Other garden bridges may cross only a dry bed of stream washed pebbles, intended only to convey an impression of a stream. Bronzes resist corrosion (especially seawater corrosion) and metal fatigue better than steel. This type, often found in east-asian style gardens, is called a Moon bridge, evoking a rising full moon. Bronzes are softer and weaker than steel, and more elastic, though bronze springs are less stiff (and so storing less energy) for the same bulk. To create a beautiful image, some bridges are built much taller than necessary. They are generally about 10 percent heavier than steel, although alloys using aluminium or silicon may be slightly less dense.

An aqueduct is a bridge that carries water, resembling a viaduct. Copper-based alloys have lower melting points than steel and are more readily produced from their constituent metals. For example, it may be a bridge carrying a highway and forbidden for pedestrians and bicycles, or a pedestrian bridge, possibly also for bicycles. Steel, of course, has wondrous properties that bronze cannot compete with. In some cases there may be restrictions in use. It is considerably less brittle than iron and has a lower casting temperature. A bridge is usually designed for trains, pedestrian or road traffic, a pipeline or waterway for water transport or barge traffic. While it develops a patina, it does not otherwise oxidize into nothingness.

There are four main types of bridges: beam bridges, cantilever bridges, arch bridges and suspension bridges. Excluding steel from the discussion, bronze is superior to iron in nearly every application. The Oxford English Dictionary traces the origin of the word bridge to an Old Norse word bryggja, meaning "landing stage, gangway, or movable pier". As ironworking improved, iron became both cheaper and stronger, eclipsing bronze in Europe by the early to mid-Middle Ages. With the advent of steel, which has a high tensile strength, much larger bridges were built, many using the ideas of Gustave Eiffel. Bronze was still used during the Iron Age, but for many purposes the weaker iron was sufficiently strong. With the rise of the Industrial Revolution in the 19th century, truss systems of wrought iron were developed for larger bridges, but iron did not have the tensile strength to support large loads. But the Bronze Age gave way to the Iron Age, perhaps because the shipping of tin around the Mediterranean (or maybe from Britain) became more limited during the major population migrations around 1200 – 1100 BC, which dramatically limited supplies and raised prices [1].

The first engineering book on building bridges was written by Hubert Gautier in 1716. Bronze was stronger than the era's iron; quality steels were not available until thousands of years later. During the 18th century there were many innovations in the design of timber bridges by Hans Ulrich, Johannes Grubenmann, and others. The earliest tin-alloy bronzes date to the late 4th millennium BC in Susa (Iran) and some ancient sites in Luristan (Iran) and Mesopotamia (Iraq). Rope bridges, 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. For Europe, the major site for tin was Britain. Brick and mortar bridges were built after the Roman era, as the technology for cement was lost then later rediscovered. The archaeologists suspect a serious disruption of the tin-trade led to the development of the Iron Age.

The Romans also had cement, which reduced the variation of strength found in natural stone. Serious bronze has always involved trade. The arch was first used by the Roman Empire for bridges and aqueducts, some of which still stand today. While copper and tin can natually co-occur, the two ores are rarely found together (an ancient site in Thailand does prove they can co-occur). The first bridges were spans made of wooden logs or planks and eventually stones, using a simple support and crossbeam arrangement. In early use, the natural impurity arsenic created a superior natural alloy; this is termed arsenical bronze, which Ötzi's axe is made of. . First used in the Bronze Age, it made tools, weapons and armor harder or more durable than their stone and copper ("Chalcolithic") predecessors.

The purpose of a bridge is to allow easier passage by providing a continuous more uniform more easily navigable route via what would otherwise be an uneven or impossible path for the particular kind of thing travelling or being transported, whether people, vehicles, trains, ships, liquids or whatever else. . Designs may be built higher than otherwise needed in order to allow other traffic (particularly ship traffic) beneath. (See table below). A bridge is a structure built to span a gorge, valley, road, railroad track, river, body of water, or any other physical obstacle. Bronze is the usual English term for a broad range of copper alloys, usually with tin as the main additive, but other elements may be the main additive (e.g., phosphor, manganese, aluminum, silicon). Pearl Harbor Memorial Bridge - USA, will be the first extradosed cable-stayed bridge constructed in the United States.

Zakim Bunker Hill Bridge - USA, built during Boston's Big Dig, the widest cable-stayed bridge. Victoria Falls Bridge - linking Zimbabwe to Zambia, built in 1905 as part of the projected Cape-Cairo railway. Vasco da Gama Bridge - Portugal, the longest bridge in Europe at 17.2 km. Trajan's bridge - Romania, ancient Roman bridge over the river Danube, only fragments visible.

Tyne Bridge - England, one of Northern England's most iconic structures. Tsing Ma Bridge - Hong Kong, the world's longest rail & road suspension bridge. Tower Bridge - London, England, and a symbol of this city. Tatara Bridge - Japan, largest span cable-stayed bridge.

Tacoma Narrows Bridge - USA, famous for its collapse due to aerodynamic effects. Sydney Harbour Bridge - Australia, arguably the best-known suspended-deck compression arch bridge. Sundial Bridge - USA, a dramatic single cantilever spar cable stayed span for pedestrians. San Francisco-Oakland Bay Bridge - USA, especially for seismic retrofit and eastern span replacement.

Québec Bridge - Canada, largest cantilever bridge in the world. Penang Bridge - Malaysia, longest bridge in Southeast Asia. Palace Bridge - St Petersburg, Russia, one of iconic images of the city. Overtoun Bridge, - Scotland, dogs have leaped to their deaths from this bridge, leading to urban legends.

Øresundbroen/Öresundsbron. Millau Viaduct - France, tallest bridge in the world. Menai Suspension Bridge - Wales, first road suspension bridge in the world. Mahatma Gandhi Setu - India, the longest river bridge in the world.

Mackinac Bridge - USA, Opened to traffic in 1957, connecting the two peninsulas of Michigan; held the title of the world's longest two tower suspension bridge between anchorages until the 1990s. Lupu Bridge- China, longest single steel arch. Lake Pontchartrain Causeway - USA, spanning Lake Pontchartrain in south Louisiana, it is the longest bridge in the world at 23.87 miles (38.41 km). Jamuna Bridge- Bangladesh, longest rail-road bridge in south asia , 2nd longest in world.

Confederation Bridge - Canada, world's longest bridge over waters that freeze. The Iron Bridge - England, the world's first iron bridge. Golden Gate Bridge - USA, arguably the most beautiful of its type. Forth Railway Bridge - Scotland, one of the most famous cantilever bridges in the world.

Akashi-Kaikyo Bridge - Japan, with the longest section span of 1.9 km.