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Bridge

Bridge

:This article is about the edifice (it is mostly an index to articles concerning specific bridge types). For other meanings, see bridge (disambiguation). bridge (disambiguation) A bridge is a structure built to span a gorge, valley, road, railroad track, river, body of water, or any other physical obstacle. Designs may be built higher than otherwise needed in order to allow other traffic (particularly ship traffic) beneath. 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.

History

The first bridges were spans made of wooden logs or planks and eventually stones, using a simple support and crossbeam arrangement. The arch was first used by the Roman Empire for bridges and aqueducts, some of which still stand today. The Romans also had cement, which reduced the variation of strength found in natural stone. Brick and mortar bridges were built after the Roman era, as the technology for cement was lost then later rediscovered. 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. During the 18th century there were many innovations in the design of timber bridges by Hans Ulrich, Johannes Grubenmann, and others. The first engineering book on building bridges was written by Hubert Gautier in 1716. 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. With the advent of steel, which has a high tensile strength, much larger bridges were built, many using the ideas of Gustave Eiffel.

Etymology

The Oxford English Dictionary traces the origin of the word bridge to an Old Norse word bryggja, meaning "landing stage, gangway, or movable pier".

Types of bridges

Bridges may be classified by their use or by their structure.

By use

A bridge is usually designed for trains, pedestrian or road traffic, a pipeline or waterway for water transport or barge traffic. In some cases there may be restrictions in use. For example, it may be a bridge carrying a highway and forbidden for pedestrians and bicycles, or a pedestrian bridge, possibly also for bicycles. An aqueduct is a bridge that carries water, resembling a viaduct.

Decorative and ceremonial 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 mind. A set of five bridges cross a sinuous waterway in an important courtyard of the Forbidden City in Beijing, China. The central bridge was reserved exclusively for the use of the Emperor, Empress, and their attendants.

Index to types of bridges and bridge related topics

Image:NagasakiMeganebashi.jpg|Arch bridge Image:Pont_du_gard.jpg|Aqueduct Image:Baileycoppename.jpg|Bailey bridge Image:UniversityBridge-1Clip.jpg|Bascule bridge Image:Small footbridge.jpg|Beam bridge Image:Concrete box girder bridge.JPG|Box girder bridge Image:ThreeTwrBrCenter.jpg|Cable-stayed bridge Image:CaissonSchematic.jpg|Caisson Image:ForthBridgeEdinburgh.jpg|Cantilever bridge Image:Puente del Alamillo.jpg|Cantilever spar cable-stayed bridge Image:Tarr steps clapper bridge.jpg|Clapper bridge Image:Australia sydney-404.jpg|Compression arch suspended-deck bridge Image:Guilford vermont covered bridge 20040820.jpg|Covered bridge Image:CurlingBridgeClip.jpg|Curling bridge Image:Fort ticonderoga drawbridge to demilune.jpg|Drawbridge Image:Hoernbruecke.jpg|Folding bridge Image:IRBSideViewClip.jpg|Inca rope bridge Image:JetwayAtVancouverBC.jpg|Jetway Image:Guilford vermont bridge covered bridge interior 20040820.jpg|Lattice bridge Image:BNSFBridgeClip.jpg|Lift bridge Image:Vallorcine footpath bridge 2003-12-13.jpg|Log bridge Image:SFTGMoonBridge.jpg|Moon bridge Image:PlateGirderUnderTracks.jpg|Plate girder bridge Image:ArmyPontoonBr.jpg|Pontoon bridge Image:Uppsala Ultunabron02 2005-06-16.jpg|Retractable bridge
(Thrust bridge) Image:ProposedSFOBBEasternSpan.jpg|Self-anchored suspension bridge Image:SegmentalBridgeFtLauderdale.jpg|Segmental bridge Image:WinnepegBridge.jpg|Side-spar cable-stayed bridge Image:CapilanoBridge.jpg|Simple suspension bridge Image:StepStoneBridge.jpg|Step-stone bridge Image:BridgeSubmerging4.jpg|Submersible bridge Image:suspension.bridge.bristol.arp.750pix.jpg|Suspension bridge Image:Railway swing bridge.jpg|Swing bridge Image:Millenium_bridge_close.jpg|Tilt bridge Image:Paying Toll on passing a Bridge From a Painted Window in the Cathedral of Tournay Fifteenth Century.png|Toll bridge Image:Newport.transporter.750pix.jpg|Transporter bridge Image:AlhambraTrestle.jpg|Trestle Image:Eastbound_over_SCB.jpg|Truss arch bridge Image:RRTrussBridgeSideView.jpg|Truss bridge Image:Conwy Castle 2.jpg|Tubular bridge Image:Toronto-bloorviaduct.jpg|Viaduct Image:NoImageYetRectFramed.png|Weigh bridge Image:BoxerwoodDotComZigZag.jpg|Zig-zag bridge

Bridge structural and evolutionary taxonomy

Zig-zag bridge Bridges may be classified by how the four forces of tension, compression, bending and shear are distributed through their structure. Most bridges will employ all of the principle forces to some degree, but only a few will predominate. 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. 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 right.

Efficiency

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. 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. The bridge taking the greatest load is by this test the most structurally efficient. 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. 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. Bridges employing only compression are relatively inefficient structurally, but may be highly cost efficient where suitable materials are available near the site. 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.

Notable bridges

- Akashi-Kaikyo Bridge - Japan, with the longest section span of 1.9 km.
- Forth Railway Bridge - Scotland, one of the most famous cantilever bridges in the world.
- Golden Gate Bridge - USA, arguably the most beautiful of its type.
- The Iron Bridge - England, the world's first iron bridge.
- Confederation Bridge - Canada, world's longest bridge over waters that freeze.
- Jamuna Bridge- Bangladesh, longest rail-road bridge in south asia , 2nd longest in world.
- 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).
- Lupu Bridge- China, longest single steel arch.
- 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.
- Mahatma Gandhi Setu - India, the longest river bridge in the world.
- Menai Suspension Bridge - Wales, first road suspension bridge in the world.
- Millau Viaduct - France, tallest bridge in the world.
- Overtoun Bridge, - Scotland, dogs have leaped to their deaths from this bridge, leading to urban legends.
- Penang Bridge - Malaysia, longest bridge in Southeast Asia.
- Québec Bridge - Canada, largest cantilever bridge in the world.
- San Francisco-Oakland Bay Bridge - USA, especially for seismic retrofit and eastern span replacement.
- Sundial Bridge - USA, a dramatic single cantilever spar cable stayed span for pedestrians.
- Sydney Harbour Bridge - Australia, arguably the best-known suspended-deck compression arch bridge.
- Tacoma Narrows Bridge - USA, famous for its collapse due to aerodynamic effects.
- Tatara Bridge - Japan, largest span cable-stayed bridge.
- Tower Bridge - London, England, and a symbol of this city.
- Tyne Bridge - England, one of Northern England's most iconic structures.
- Trajan's bridge - Romania, ancient Roman bridge over the river Danube, only fragments visible.
- Vasco da Gama Bridge - Portugal, the longest bridge in Europe at 17.2 km.
- Victoria Falls Bridge - linking Zimbabwe to Zambia, built in 1905 as part of the projected Cape-Cairo railway.
- Zakim Bunker Hill Bridge - USA, built during Boston's Big Dig, the widest cable-stayed bridge.

External links

- [http://www.structurae.de/en/ Structurae] - International Database and Gallery of Structures.
- [http://www.asce.org/history/hp_bridges.html American Society of Civil Engineers] History and Heritage of Civil Engineering - Bridges
- [http://www.historicbridges.org/index.htm Historic Bridges of Michigan and Elsewhere] Photos, information, and maps of historic bridges in and around Michigan. Also has a links page with links to bridge databases in other regions of the U.S.A.
- [http://www.brantacan.co.uk/bridges.htm Bridge Building — Art and Science] Comprehensive explanations about bridges.
- [http://www.garrettsbridges.com/index.html Model Bridge Building]
- [http://pghbridges.com/basics.htm Bridge Basics] A guide to bridge terminology and styles
- [http://www.chinapage.com/bridge/shanghai/lupu/lupu.html Shanghai lupu] Chinese bridge site showing suspended deck arch construction and completion.
- [http://www.bridgebuilder-game.com BridgeBuilder] - Great game where you design a bridge and see if a train will drive over it safely.
- [http://finance.groups.yahoo.com/group/RRbridge/ RRbridge]- Discussion group focused on railroad bridges, trestles, and viaducts. Hosted by Yahoo! Groups
- [http://filebox.vt.edu/users/aschaeff/titlepage.html Bridge disasters]
- [http://www.nireland.com/bridgeman/Dictionary.htm A dictionary of bridge terms]
- [http://bridges.lib.lehigh.edu/BookListpage.html/ Digital Bridge Library at Lehigh University]
- [http://bobjagendorf.smugmug.com/gallery/119358 Bridge Photos]
- [http://flickr.com/photos/tags/bridge Flickr: Photos tagged with bridge] Category:Buildings and structures
- Category:Coastal construction ko:다리 ms:Jambatan ja:橋 simple:Bridge th:สะพาน

Bridge (disambiguation)

Bridge may mean:
- Bridge (structure), a structure built so that a transportation route can cross above an obstacle.
- Bridge (music), an interlude that connects two parts of song.
- Bridge (dentistry), a prosthesis used in place of missing teeth.
- Bridge (card game)
- Bridge (ship), from which a ship is commanded.
- Bridge (exercise), most commonly the balancing of the body on the head and feet.
- Bridge (instrument), the device that anchors the strings to or holds the strings above the body of a string instrument, such as a violin or guitar.
- Bridge pattern, a computer science design used to separate an abstraction and its actual implementation.
- Bridge loan, a short-term loan to cover a gap in time until a new long-term financing is realised.
- Bridge rectifier, an electronic circuit for converting alternating current to direct current.
- Wheatstone bridge, an electronic circuit for comparing resistors, capacitors or inductors to high standards of accuracy.
- Network bridge, an electronic device used to connect two computer or telephone network segments.
- People named Bridge, from List of people by name. Places with the name Bridge:
- Bridge, Kent, a place in Kent, England.
- Scotland has many place names in the style of Bridge of Allan. ja:ブリッジ

Gorge

A gorge is a narrow passage between steep mountains or hills. See also: canyon
- Avon Gorge in Bristol, England
- Cataract Gorge in Launceston, Australia
- Cheddar Gorge in Somerset, England
- Columbia River Gorge in the Pacific Northwest section of USA
- The Flume Gorge in Franconia, New Hampshire, USA
- Ironbridge Gorge in Shropshire, England
- Mather Gorge between Maryland and Virginia, USA
- Red River Gorge in Kentucky, USA
- Royal Gorge in Colorado, USA
- Three Gorges in China
- Vikos Gorge in Greece Category:Geography

Valley

:This article is about the physical-geographic term. For places named "Valley" see Valley (disambiguation). Valley (disambiguation)-Iceland]] A valley is a landform, which can range from a few square miles (square kilometers) to hundreds or even thousands of square miles (square kilometers) in area. It is typically a low-lying area of land, surrounded by higher areas such as mountains or hills. Valleys are formed by numerous geographical processes. Glacial valleys, which are usually U- rather than V-shaped, were formed tens of thousands of years ago (most likely during the last Ice Age) by the massive erosive power of glaciers. Several glacial valleys can be found in the English Lake District and many can be found in Alpine countries. Rift valleys, such as the Great Rift Valley, are formed by the expansion of the Earth's crust due to tectonic activity beneath the Earth's surface. Valleys are, however, most commonly formed by fluvial activity (the action of running water, such as rivers), which erodes the landscape.

Hollows

A hollow is loose name for a valley in the earth. It is commonly used in New England to describe such geographic features. Hollows may be formed by river valleys such as Mansfield Hollow or they may be relatively dry clefts with a notch like characteristic in that they have a height of land and consequent water divide in their bases. A hollow such as this is Boston Hollow.

Famous valleys

- California Central Valley
- Copper Canyon
- Death Valley
- Grand Canyon
- Great Rift Valley
- Loire Valley
- Napa Valley
- Rhone Valley
- Shenandoah Valley
- Valley of the Kings
- San Fernando Valley
- Santa Clara Valley (Silicon Valley)

Extraterrestrial valleys

Planets and moons other than the Earth can also have valley-like features. Lunar valleys can be formed due to a linked chain of impact craters. Smaller valleys, known as rilles, can be formed due lava flows or because of contractions in cooling lava sheets. The Valles Marineris formation on Mars is a valley nearly 4000 km in length. It was originally formed by tectonic forces, but has been expanded by erosion.

Water

:This article focuses on water as it is experienced in everyday life. See water (molecule) for information on the chemical and physical properties of pure water (H₂O, hydrogen oxide). Water (from the Old English word wæter; c.f German "Wasser", from PIE
- wod-or, "water") is a tasteless, odorless, and nearly colorless (it has a slight hint of blue) substance in its pure form that is essential to all known forms of life and is known also as the most universal solvent. Water is an abundant substance on Earth. It exists in many places and forms. It appears mostly in the oceans and polar ice caps, but also as clouds, rain water, rivers, freshwater aquifers, and sea ice. On the planet, water is continuously moving through the cycle involving evaporation, precipitation, and runoff to the sea. Water fit for human consumption is called potable water. This natural resource is becoming more scarce in certain places as human population in those places increases, and its availability is a major social and economic concern.

Molecular properties

Forms of water

potable water] Water takes many different shapes on earth: water vapor and clouds in the sky, waves and icebergs in the sea, glaciers in the mountain, aquifers in the ground, to name but a few. Through evaporation, precipitation, and runoff, water is continuously flowing from one form to another, in what is called the water cycle. Because of the importance of precipitation to agriculture, and to mankind in general, different names are given to its various forms: while rain is common in most countries, other phenomena are quite surprising when seen for the first time. Hail, snow, fog or dew are examples. When appropriately lit, water drops in the air can refract sunlight to produce rainbows. Similarly, water runoffs have played major roles in human history as rivers and irrigation brought the water needed for agriculture. Rivers and seas offered opportunity for travel and commerce. Through erosion, runoffs played a major part in shaping the environment providing river valleys and deltas which provide rich soil and level ground for the establishment of population centers. Water also infiltrates the ground and goes into aquifers. This groundwater later flows back to the surface in springs, or more spectacularly in hot springs and geysers. Groundwater is also extracted artificially in wells. Because water can contain many different substances, it can taste or smell very differently. In fact, humans and other animals have developed their senses to be able to evaluate the drinkability of water: animals generally dislike the taste of salty sea water and the putrid swamps and favor the purer water of a mountain spring or aquifer.

Water in biology

From a biological standpoint, water has many distinct properties that are critical for the proliferation of life that set it apart from other substances. Water carries out this role by allowing organic compounds to react in ways that ultimately allows replication. It is a good solvent and has a high surface tension, and thus allows organic compounds and living things to be transported in it. Fresh water has its greatest density at 4°C, then becoming less dense as it freezes or heats up from this point. As a stable, polar molecule prevalent in the atmosphere, it plays an important atmospheric role as an absorber of infrared radiation, crucial in the atmospheric greenhouse effect without of which, the average surface temperature would be −18° Celsius. Water also has an unusually high specific heat, which plays many roles in regulating global and regional climate, such as the Gulf Stream climate, allowing life to survive. Water is a very good solvent, chemically not unlike ammonia, and dissolves many types of substances, such as various salts and sugar, and facilitates their chemical interaction, which aids complex metabolisms. Some substances, however, do not mix well with water, including oils and other hydrophobic substances. Cell membranes, composed of lipids and proteins, take advantage of this property to carefully control interactions between their contents and external chemicals. This is facilitated somewhat by the surface tension of water. Water drops are stable due to the high surface tension of water caused by the strong intermolecular forces called cohesive forces. This can be seen when small quantities of water are put onto a nonsoluble surface such as polythene: the water stays together as drops. On extremely clean glass the water may form a thin film because the molecular forces between glass and water molecules (adhesive forces) are stronger than the cohesive forces. This property plays a key role in plant transpiration. A simple but environmentally important and unique property of water is that its common solid form, ice, floats on the liquid. This solid phase is less dense than liquid water, due to the geometry of the strong hydrogen bonds which are formed only at lower temperatures. For almost all other substances and for all other 11 uncommon phases of water ice except ice-XI, the solid form is more dense than the liquid form. Fresh water is most dense at 4°C, and will sink by convection as it cools to that temperature, and if it becomes colder it will rise instead. This reversal will cause deep water to remain warmer than shallower freezing water, so that ice in a body of water will form first at the surface and progress downward, while the majority of the water underneath will hold a constant 4°C. This effectively insulates a lake floor from the cold. While this behavior may seem obvious, even intuitive, it should be noted that almost all other chemicals are denser as solids than they are as liquids, and freeze from the bottom up. Life on earth has evolved with and adapted itself to the important features of water. The existence of abundant liquid, vapor and solid forms of water on Earth has been an important factor in the abundant colonization of Earth's various environments by life-forms adapted to those varying and often extreme conditions. Civilizations have historically flourished around rivers and major waterways; Mesopotamia, the so-called cradle of civilization, is situated between two major rivers. Large metropolises like London, Paris, New York, and Tokyo owe their success in part to their easy accessibility via water and the resultant expansion of trade. Islands with safe water ports, like Singapore and Hong Kong, have flourished for precisely this reason. In places such as North Africa and the Middle East, where water is scarcer, access to clean drinking water was and is a major factor in human development.

Astronomical position of Earth and impact on its water

Mesopotamia The coexistence of the solid, liquid, and gaseous phases of water on Earth is vital to the origin, evolution, and continued existence of life on Earth. However, if the Earth's location in the solar system were even marginally closer or further from the Sun (ie, a million miles or so), the conditions which allow the three forms to be present simultaneously would be far less likely to exist. Earth's mass allows gravity to hold an atmosphere. Water vapor and carbon dioxide in the atmosphere provides a greenhouse effect which helps maintain a relatively steady surface temperature. If Earth were less massive, a thinner atmosphere would cause temperature extremes preventing the accumulation of water except in polar ice caps (as on Mars). According to the solar nebula model of the solar system's formation, Earth's mass may be largely due to its distance from the Sun. The distance between Earth and the Sun and the combination of solar radiation received and the greenhouse effect of the atmosphere ensures that its surface is neither too cold nor too hot for liquid water. If Earth were more distant, most water would be frozen. If Earth were nearer to the Sun, its higher surface temperature would limit the formation of ice caps, or cause water to exist only as vapor. In the former case, the low albedo of oceans would cause Earth to absorb more solar energy. In the second case, a runaway greenhouse effect and inhospitable conditions similar to Venus would result. It has been proposed that life itself may maintain the conditions that have allowed its continued existence. The surface temperature of Earth has been relatively constant through geologic time despite varying solar flux, indicating that a dynamic process governs Earth's temperature via a combination of greenhouse gases and surface or atmospheric albedo. This proposal is known as the Gaia hypothesis.

Human uses of water

Gaia hypothesis All known forms of life depend on water. Water is a vital part of many metabolic processes within the body. Significant quantities of water are used during the digestion of food. (Note however that some bacteria and plant seeds can enter a cryptobiotic state for an indefinite period when dehydrated, and come back to life when returned to a wet environment) About 72% of the fat free mass of the human body is made of water. To function properly the body requires between one and seven litres of water per day to avoid dehydration, the precise amount depending on the level of activity, temperature, humidity, and other factors. It is not clear how much water intake is needed by healthy people. However, for those who do not have kidney problems, it is rather difficult to drink too much water, but (especially in warm humid weather and while exercising) dangerous to drink too little. People do often drink far more water than necessary while exercising, however, putting them at risk of water intoxication, which is frequently fatal. The "fact" that a person should consume eight glasses of water per day cannot be traced back to a scientific source. However, leading dieticians and nutritionists will tell you that this is the RDI (Recommended Daily Intake) of water. [http://ajpregu.physiology.org/cgi/content/full/283/5/R993]. The latest dietary reference intake report by the National Research Council recommended 2.7 liters of water total (including food sources) for women and 3.7 liters for men[http://www.iom.edu/report.asp?id=18495]. Water is lost from the body in urine and feces, through sweating, and by exhalation of water vapor in the breath. Humans require water that does not contain too much salt or other impurities. Common impurities include chemicals and/or harmful bacteria, such as crypto sporidium. Some solutes are acceptable and even desirable for perceived taste enhancement and to provide needed electrolytes.

Water as a precious resource

:See water resources for information about fresh water supplies. fresh water Because of the growth of world population and other factors, the availability of drinking water per capita is shrinking. The issue of water shortage can be solved through more production, better distribution and less waste of it. For this reason, water is a strategic resource for many countries. Many battles and wars, such as the Six-Day War in the Middle East, have been fought to gain access to it. Experts predict more trouble ahead because of the world's growing population, increasing contamination through pollution, and global warming. UNESCO's World Water Development Report (WWDR, 2003) from its World Water Assessment Program indicates that, in the next 20 years, the quantity of water available to everyone is predicted to decrease by 30%. 40% of the world's inhabitants currently have insufficient fresh water for minimal hygiene. More than 2.2 million people died in 2000 from diseases related to the consumption of contaminated water or drought. In 2004, the UK charity WaterAid reported that a child dies every 15 seconds due to easily preventable water-related diseases. Some have predicted that clean water will become the "next oil", making Canada, with this resource in abundance, possibly the richest country in the world.

Regulating water distribution

Drinking water is often collected at springs or extracted from artificial borings in the ground, or wells. Building more wells in adequate places is thus a possible way to produce more water assuming the aquifers can supply an adequate flow. Other water sources are the rainwater and river or lake water. This surface water, however, must be purified for human consumption. This may involve removal of undissolved substances, dissolved substances and harmful microbes. Popular methods are filtering with sand which only removes undissolved material while chlorination and boiling kill harmful microbes. Distillation does all three functions. More advanced techniques exist, such as reverse osmosis. Desalination of abundant ocean or seawater is a more expensive solution used in coastal arid climates. The distribution of drinking water is done through municipal water systems or as bottled water. Governments in many countries have programs to distribute water to the needy at no charge. Others argue that the market mechanism and free enterprise are best to manage this rare resource, and to finance the boring of wells or the construction of dams and reservoirs. Reducing waste, that is using drinking water only for human consumption, is another option. In some cities, such as Hong Kong, sea water is extensively used for flushing toilets citywide in order to conserve fresh water resources. Polluting water may be the biggest single misuse of water; to the extent that a pollutant limits other uses of the water, it becomes a waste of the resource, regardless of benefits to the pollutor. Pharmaceuticals consumed by humans often end up in the waterways and can have detrimental effects on aquatic life if they bioaccumulate and if they are not biodegradable.

The impact of water on human culture

Water is considered a purifier in most religions, including Christianity, Islam, Judaism, and Shinto. For instance, baptism in Christian churches is done with water. In addition, a ritual bath in pure water is performed for the dead in many religions including Judaism and Islam. In Islam, the daily Salah can only be done after ablution (Wodoo), that is, washing parts of the body in clean water. In Shinto, water is used in almost all rituals to cleanse a person or an area. Water is often believed to have spiritual powers. In Celtic mythology, Sulis is the local goddess of thermal springs; in Hinduism, the Ganga is also personified as a goddess. Alternatively, gods can be patrons of particular springs, river or lakes: for example in Greek and Roman mythology, Peneus was a river god, one of the three thousand Oceanids. The Greek philosopher Empedocles held that water is one of the four classical elements along with fire, earth and air, and was regarded as the ylem, or basic stuff of the universe. Water was considered cold and moist. In the theory of the four bodily humours, water was associated with phlegm. Water was also one of the Five Elements in traditional Chinese philosophy, along with earth, fire, wood, and metal. A common misconception about water is that it is a powerful conductor of electricity. Any electrical properties observable in water are due to the ions of mineral salts and carbon dioxide dissolved in it. Water does self-ionize (two water molecules become one hydroxide anion and one hydronium cation), but only at a very slight, almost immeasurable level. Pure water can also be electrolized into oxygen and hydrogen gases but without any dissolved ions, this is a very slow process and thus very little current is conducted. Many bottled water companies exploit another common misconception, advertising both purity and taste, even though pure water is tasteless.

External links

- [http://www.lsbu.ac.uk/water/phase.html Phase diagrams of water]
- [http://www.publicforuminstitute.org/issues/oceans/index.htm Oceans and Water Issues Page]
- [http://www.greenfacts.org/water-disinfectants/index.htm Scientific Facts on Water disinfectants] A faithful summary by GreenFacts of a leading scientific consensus report on Drinking Water Disinfectants published by the International Programme on Chemical Safety of the WHO.
- [http://www.hkc22.com/residentialwater.html Residential water problems and markets] Study paper from Helmut Kaiser Consultancy
- [http://www.hkc22.com/watermarketsworldwide.html Water markets worldwide] Study paper from Helmut Kaiser Consultancy
- [http://www.worldwaterforum.org/ World Water Forum]
- [http://www.unesco.org/water/wwap/ World Water Assessment Program]
- [http://unesdoc.unesco.org/images/0012/001295/129556e.pdf United Nations' World Water Development Report]
- [http://www.gemswater.org/ United Nations GEMS/Water Programme]
- [http://www.lsbu.ac.uk/water/ Water Structure and Behaviour]
- [http://www.wateraid.org/ WaterAid]
- [http://www.sahra.arizona.edu/newswatch/ SAHRA—Global Water Newswatch]
- [http://www.siwi.org/ Stockholm International Water Institute] (SIWI)
- [http://www.c-win.org/ California Water Impact Network (C-WIN)]
- [http://news.bbc.co.uk/2/hi/science/nature/3752590.stm BBC: The water debate]
- [http://www.geocities.com/tapvsbottled/ Tap Water Vs Bottled Water] - Interesting site providing facts about tap and bottled water.
- [http://www.emagazine.com/september-october_2003/0903feat1.html E the Environmental Magazine piece on bottled water] (Oct 2003).
- [http://www.iapws.org/ International Association for the Properties of Water and Steam]
- [http://ga.water.usgs.gov/edu/watercycle.html US Geological Survey: Comprehensive discussion of the water cycle, in many languages]
- [http://www.dartmouth.edu/~etrnsfer/water.htm Why is water blue?]
- [http://www.water.org.uk/home/resources-and-links/water-for-health/ask-about/adults Water requirements in adults]
- [http://www.hkc22.com/environmentaltechnology.html/ Climate change raises markets for environmental technology, drinking water and clean energies]

References

- OA Jones, JN Lester and N Voulvoulis, Pharmaceuticals: a threat to drinking water? TRENDS in Biotechnology 23(4): 163, 2005
- Category:Beverages Category:Hydrology Category:Materials Category:Natural resources Category:Nutrition zh-min-nan:Chúi als:Wasser ko:물 ja:水 ms:Air simple:Water th:น้ำ

Logging

:For another article about a different type of logging, see data logging. (Logging sometimes also refers to a technique used in the oilfield business to measure geological parameters of an oil or gas well. See well logging.) well logging Logging is the practice of cutting down trees, then cutting out their central boles (the clear trunk or central stem) and possibly branches in order to use the wood as an economic resource or to clear forest land for conversion to another use. Standing trees viewed as a potential economic resources are termed timber. Most conventional logging is either for pulpwood production for the manufacture of paper products or for sawlogs for lumber production. In the United States, standard sawlogs are sixteen feet long. Trees may be referred to as "two-saw-log-trees", for instance, meaning that they have a clear bole for at least 34 or so feet (allowing for the remaining stump). A significant amount of logging is also done for firewood production, and, today, a very large and growing amount of logging is being done for chipwood production.

Logging activites

- Felling and delimbing trees - done using a chain saw or a feller buncher
- Yarding - Transporting the trees from the stump to a landing can be done with a skidder or a forwarder
- bucking - Cutting the tree into logs is done at the landing, again using a chain saw. In cut-to-length logging felling, delimbing and bucking are all done with a harvester
- Loading the logs onto trucks - done with a loader equiped with a grapple
- Hauling the logs to a mill - done with a log truck
- Preparing the site for regeneration - includes managing slash and rehabilitating the site

Silviculture systems

harvester harvester

Clearcutting

The most common and most criticized method of timber harvest in industrial operations is clearcutting, a practice that removes essentially all the trees in a selected area. In the case of a pure-age stand, such as a plantation, or in certain even-aged mature forests, such as some of the virgin Douglas-fir stands of the West, virtually all trees are cut. . Clearcutting is also the most economically-efficient way to remove timber but treatment following a clearcut can lead to higher costs. Large poorly planned clearcuts are far more destructive than cuts that take into consideration natural topography, and bioregions. There are supportable claims that clearcutting can be an ecologically healthy forestry practice, mimicking the effects of a natural disturbance. The effects of sustainable clearcutting can mimic the effects of a forest fire or other natural disturbance in a number of important ways. Conscientious logging will leave standing snags and a mosic of small "residual patches" for wildlife, and organic matter such as "slash piles" of unusable material are left on-site as ash to fertilize the soil or as partly-burnt wood that will quickly decay into the soil. If logged on frozen ground with low ground pressure machinery, or even horses, the ground can be left generally undisturbed and unbroken which can let groundcover regenerate quickly. In the case of a poorly planned larger (over 1 km²) clearcut, there are few or no residual patches or wildlife snags left behind and the ground will be highly disturbed and compacted; erosion and poor forest regeneration will result. Most forest managers do not consider large clearcuts to be appropriate in an forest managed for multiple uses. Some forest types are especially intolerant of clearcutting exposing soils to direct sun and winter rains, which damages soil nutrients and fungi required for healthy forests.

Selection cut

Selection cutting is the practice of removing mature timber or thinning to improve the a timber stand. This system is used to maintain uneven-aged stands to protect forest soils and to maintain wildlife habitat. A particular type of selective cutting that targets only the highest-quality trees of certain species is termed high-grading, which ultimately results in much lower-quality woodlands. If the best trees are cut removing them from the seedstock, an evolutionary pressure towards lower quality results. Selection cutting may include opening up areas to allow tree species that require large amount of light to grow but that are not large enough to meet the legal defination of a clearcut.

Overstory removal

Overstory removal or sheltwood cutting is a variation of select cutting. In this method all the large trees are taken and the understory of saplings and smaller trees are left for regeneration. Overstory removal requires care be used to avoid residual stand damage. seedstock. This photo demonstrates extreme soil disturbance typical of poor forestry practices.]] seedstock seedstock

Logging and the environment

Harvesting on steep slopes can lead to erosion. Harvesting adjacent to streams can decrease water quality and increase water tempertures. Logging on wetlands or saturated soils can cause ruts, change drainage patterns. These problems can be mitagated by using best management practices. These practices set standards for building roads reducing erosion and establishment of riparian strips. Harvesting in high value ecologically sensitive lands can lead to habitat loss. Ecologically important lands should be set aside as reserves. A problem with poorly operated forestry practices, especially in the eastern North American hardwood forests, is the problem of colonization of the forest area by invasive exotics. In a normal, intact forest, or even in a carefully-managed woodlot, such species find it very difficult to gain a toe-hold.

Logging roads

As most logging is done far from developed areas, roads must be constructed for access. These are narrow, unpaved, and usually have no hard shoulder or guardrails. Bridges, if any, are invariably only wide enough for one vehicle. The most common traffic on these roads will be logging trucks, which, when loaded, can carry up to 4,500 kg of wood. As such, drivers on logging roads generally follow one simple rule: A loaded logging truck has the right of way. This is regardless of what the local motor vehicle code may actually say. In areas where this practice is regulated (or is supposed to be) non-highway roads with heavy logging traffic may be "radio-controlled", which is to say a CB on board any vehicle on the road is advised for safety reasons. Construction of these roads, especially on steep slopes, increases the risk of erosion and landslides which can lead to increases in downstream sedimentation. The major source of sediment, (estimated to be about 90 % ) from erosion in logging operations is from logging roads, which continues long after operations are completed in the area. The decommissioning of these roads involves the restoring of natural habitat, which can be quite expensive, usually as much as it cost to construct the road in the first place. However, a new alternative, mycofiltration, which is the use of mushrooms to prevent erosion, has been developed at a far lesser expense. The cost to the public (in public forests) of such road-building varies with each jurisdiction and the type of logging licence. Although many roads are justified to the public as providing access for recreational and other non-logging users, they are often quickly "decommissioned" after their use to log extraction is at an end, and become relatively useless to other vehicular users. Mountainbikers and hikers and others still can access these roads, but they are not maintained.

Forest regeneration, silviculture and biodiversity

mushroom In clearcuts where natural regeneration is poor, sound forestry legislation will demand that a logging company plant seedlings to aid the natural regeneration of the forest. Some argue that treeplanting leads to a "monoculture" forest which destroys the biodiversity of the area. Most seedlings used in reforestation come from the seeds found in the recently cut forest as these trees are naturally adapted to the area. In many areas multiple species will be planted according to the smaller ecoregions of the cutblock ie) lodgepole pine, white or black spruce, cedar, etc. However, clearcutting exposes previously shaded forest soils to direct sun and rainstorms which damage the microbiol diversities required for healthy forest growth. Riparian strips or zoning is an important forest management practice in which trees are left standing along waterways to protect the banks and water quality. Failure to do so has historically exacerbated flooding, erosion and siltation, and caused local extirpations of sensitive plant and animal species. Some of the most marked effects of large-scale clearcutting, including the stream corridors, has been seen in the American Pacific Northwest, where salmon streams have lost their salmon-supporting capability, and local populations of salmon and even subspecies have become extinct as a result. salmon

The negative portrayal of logging by the media and popular culture

The logging industry is often portrayed in the media and popular culture as one of the most ecologically destructive corporate practices on earth. However, logging companies contend that despite some notable cases of severe environmental degradation by large, multinational logging operations, agriculture, livestock grazing, mineral mining, the petroleum industry and urban sprawl are even greater contributors to deforestation and ecological degradation. As an example, they cite that a house built out of steel, plastic and concrete requires more energy and non-renewable resources to produce than a house built with wood products.

External links

- [http://www.greenpeace.ca/boreal Boreal forests]
- [http://www.kleercut.net Consumers companies linked to forest destruction]
- [http://earthobservatory.nasa.gov/Library/Deforestation NASA Earth Observatory]
- [http://memory.loc.gov/cgi-bin/query/S?ammem/papr:@FILREQ(@field(TITLE+@od1(Logging+in+Maine++))+@FIELD(COLLID+workleis)) Movie of logging in Maine, 1906] Category:Forestry Category:Resource extraction

Plank

Plank most commonly refers to a flat piece of timber, sawn and planed; it is technically distinguished from a board by its greater thickness, and should measure from 2 to 4 inches (~5 to 10 cm) in thickness and from 10 to 11 inches (~25 to 28 cm) in width. ---- Plank may also refer to:
- an individual article in a political platform.
- Plank, a fictional character in the animated series Ed, Edd n Eddy. Plank is a short plank of wood with a drawn-on mouth and eyes. Johnny is Plank's best friend and carries him around. Johny talks to him, but it is not known whether it's Johnny's imagination, or if Plank really speaks, although Johnny is the only one that seems to be able to hear him. (The viewer cannot hear what Plank says.) Plank also moves, but only when no-one is looking, or it could be Johnny moving him.
- The Plank, a noted British silent comedy film, made in 1967. Written by Eric Sykes, it stars Sykes, Roy Castle, Tommy Cooper, Jim Dale, Jimmy Edwards, Hattie Jacques, Stratford Johns, and John Junkin. There was also a later television remake. details required
- Plank Films, an independent Film Group based in the UK. Also home to Plank Films Mobile which produces Video Reviews, Footage, Help Guides and more for all things PDA gaming! [http://www.plankfilms.com Plank Films], [http://www.plankfilms.com/pfm Plank Films Mobile]
- Plank, a fictional character in the film Lock, Stock and Two Smoking Barrels

Arch

An arch is a curved structure capable of spanning a space while supporting significant weight (e.g. a doorway in a stone wall). The arch was developed in Mesopotamia, Assyria, Egypt and Etruria. It was later refined in Ancient Rome. The arch became an important technique in cathedral building and is still used today in some modern structures as for example in bridges.

Technical aspects

The arch is significant because, in theory at least, it provides a structure which eliminates tensile stresses in spanning an open space. All the forces are resolved into compressive stresses. This is useful because several of the available building materials such as stone, cast iron and concrete can strongly resist compression but are very weak when tension, shear or torsional stress is applied to them. By using the arch configuration, significant spans can be achieved. This same principle holds when the force acting on the arch is not vertical such as in spanning a doorway, but horizontal, such as in arched retaining walls or dams. Even when using concrete, where the structure may be monolithic, the principle of the arch is used so as to benefit from the concrete's strength in resisting compressive stress. Where any other form of stress is raised, it has to be resisted by carefully placed reinforcement rods or fibres. (See Arch bridge.) The following gallery shows examples of arch forms displayed in roughly the order in which they were developed. Image:Treledsbåge.png|Triangular arch Image:Rundbåge.png|Round arch or Semi-circular arch Image:Segmentbåge.png|Segmental arch Image:Stigande båge.png|Unequal round arch or Rampant round arch Image:Lansettbåge.png|Lancet arch Image:Spetsbåge.png|Equilateral pointed arch Image:Skulderbåge.png|Shouldered flat arch Image:Trepassbåge.png|Three-foiled cusped arch Image:Hästskobåge.png|Horseshoe arch Image:Korgbåge.png|Three-centred arch Image:Ellipsbåge.png|Elliptical arch Image:Draperibåge.png|Inflexed arch Image:Kölbåge.png|Ogee arch Image:Karnisbåge.png|Reverse ogee arch Image:Tudorbåge.png|Tudor arch Image:Parabelbåge.png|Catenary or Parabolic arch Parabolic arch

Construction

An arch requires all of its elements to hold it together. This raises the interesting question of how an arch is actually constructed. One simple answer is to build a frame (historically, of wood) which exactly follows the form of the underside of the arch. This is known as a centre or centring. The voussoirs are laid on it until the arch is complete and self-supporting. For an arch higher than head height, scaffolding would in any case be required by the builders, so the scaffolding can be combined with the arch support. Occasionally arches would fall down when the frame was removed if construction or planning had been incorrect. (The A85 bridge at Dalmally, Scotland suffered this fate on its first attempt, in the 1940s).

History

Arches were used by the Egyptian, Babylonian, Greek and Assyrian civilizations for underground structures such as drains and vaults, but the ancient Romans were the first to use them widely above ground although it is thought that Romans learned it from the Etruscans. The so-called Roman arch is semicircular, and built from an odd number of arch bricks (in modern architectural parlance, these are called voussoirs). The capstone or keystone is the topmost stone in the arch. This shape is the simplest to build, but not the strongest. There is a tendency for the sides to bulge outwards, which must be counteracted by an added weight of masonry to push them inwards. The semicircular arch can be flattened to make an elliptical arch. The horseshoe arch is based on the semicircular arch, but its lower ends are extended further round the circle until they start to converge. It was used in Spanish Visigothic architecture, Islamic architecture and mudéjar architecture, as in the Great Mosque of Damascus and in later Moorish buildings. It was used for decoration rather than for strength. The semicircular arch was followed in Europe by the pointed Gothic arch or ogive, whose centreline more closely followed the forces of compression and which was therefore stronger. This design had been used by the Assyrians as early as 722 BC. The parabolic and catenary arches are now known to be the theoretically strongest forms. The arch was used in some bridges in China since the Song dynasty. Song dynasty design.]]

Other types

A dome is a three-dimensional application of the arch. Igloos are notable early structures making use of domes. A special form of the arch is the triumphal arch, usually built to celebrate a victory in war. The most famous example of this is the Arc de Triomphe in Paris, France. Natural rock formations may also be referred to as 'arches'. These natural arches are formed by erosion rather than being carved or constructed by man. See Arches National Park for examples.

References

- pp. 27-8 Category:Architectural elements Category:Arch bridges ja:アーチ th:อาร์ช

Aqueduct

:This article is about the structure aqueduct, for the racecourse see Aqueduct Racetrack. Aqueduct Racetrack, a Roman era aqueduct circa 19 BC, it is one of France's top tourist attractions at over 1.4 million visitors per year, and a World Heritage Site.]] An aqueduct is an artificial (man-made) channel that is constructed to convey water from one location to another. The word derives from the Latin words aqua, "water", and ducere, "to lead". Many aqueducts are raised above the landscape, resembling bridges rather than rivers. Sufficiently large aqueducts may also be usable by ships. They are similar to viaducts, but carry water instead of a road or railway. While a road bridge often carries the roadway at a more elevated level than the rest of the road, such a variation of height is not possible for an aqueduct.

History

Although famously associated with the Ancient Romans, aqueducts were devised centuries earlier in the Middle East, where peoples such as the Babylonians and Egyptians built sophisticated irrigation systems. Roman-style aqueducts were used as early as the 7th century BC, when the Assyrians built a limestone aqueduct 30 feet (10 m) high and 900 feet (300 m) long to carry water across a valley to their capital city, Nineveh. The full length of the aqueduct ran for 50 miles (80 km). The Romans constructed numerous aqueducts to supply water to cities and industrial sites. The city of Rome itself had the largest concentration, with water being supplied by eleven aqueducts constructed over a period of 500 years. Their combined length was nearly 260 miles (350 km). However, only 29 miles (47 km) were above ground, as most Roman aqueducts were constructed below the surface. The Eifel Aqueduct in Germany provides a very well-preserved example of this type. This method of conveyance helped to keep the water free from disease (the carcasses of animals would not be able to get into the aqueduct) and helped protect them from enemy attack. The longest Roman aqueduct, 87 miles (141 km) in length, was built in the 2nd century AD to supply Carthage in what is now Tunisia. Roman aqueducts were extremely sophisticated constructions. They were built to remarkably fine tolerances, and of a technological standard that was not to be equaled for over 1000 years after the fall of the Roman Empire. For example, the aqueduct of Pont du Gard in Provence had a gradient of only 34 cm per km (1:3,000), descending only 17 m vertically in its entire length of 31 miles (50 km). Powered entirely by gravity, they transported very large amounts of water very efficiently (the Pont du Gard carried 20,000 cubic meters a day). Sometimes, where depressions deeper than 50 m had to be crossed, gravity pressurised pipelines called inverted siphons were used to force water uphill (although they almost always used venter bridges as well). Modern hydraulic engineers use similar techniques to enable sewers and water pipes to cross depressions. sewer.]] Much of the expertise of the Roman engineers was lost in the Dark Ages, and in Europe the construction of aqueducts largely ceased until the 19th century. Water was instead usually supplied through the digging of wells, though this could cause serious public health problems when local water supplies became contaminated. One notable exception was the New River, a man-made waterway in England, opened in 1613 to supply London with fresh drinking water over a distance of 38 miles (62 km). The development of canals provided another spur to aqueduct building. However, it was not until the 19th century that aqueduct building resumed on a large scale to supply fast-growing cities and water-hungry industries. The developments of new materials (such as cast iron) and new technologies (such as steam power) enabled significant improvements to be made. For instance, cast iron permitted the construction of larger, more highly pressurised inverted siphons, while steam- and electrically-powered pumps enabled a major increase in the quantity and speed of water flow. England led the world in aqueduct construction, with notable examples being built to convey water to Birmingham, Liverpool and Manchester. The largest aqueducts of all have been built in the United States to supply that country's biggest cities. The Catskill Aqueduct carries water to New York over a distance of 120 miles (190 km), but it is dwarfed by aqueducts in the far west of the country, most notably the Colorado River Aqueduct, which supplies the Los Angeles area with water from the Colorado River nearly 250 miles (400 km) to the east. Although such aqueducts are undoubtedly great engineering achievements, the huge quantity of water that they transport has resulted in serious environmental damage from the depletion of river water.

Uses of aqueducts

Colorado River, Japan]] Historically, many agricultural societies have constructed aqueducts to irrigate crops. Archimedes invented the water screw to raise water for use in irrigation of croplands. Another widespread use for aqueducts is to supply large cities with clean drinking water. Some of the famed Roman aqueducts still supply water to Rome today. In California, USA, three large aqueducts supply water over hundreds of miles to the Los Angeles area. Two are from the Owens River area and a third is from the Colorado River. In more recent times, aqueducts were used for transportation purposes to allow canal barges to cross ravines or valleys. During the Industrial Revolution of the 18th century, many aqueducts were constructed as part of the general boom in canal-building. In modern civil engineering projects, detailed study and analysis of open channel flow is commonly required to support flood control, irrigation systems, and large water supply systems when an aqueduct rather than a pipeline is the preferred solution. The aqueduct is a simple way to get water to other ends of a field.

Notable aqueducts

Navigable aqueducts

- aqueduct near Roelofarendsveen, Netherlands: carries the Ringvaart canal over the A4 highway and the HSL being constructed, which are situated on land below the level of the canal (and below sea level)
- Gouwe aqueduct, near Gouda, Netherlands: carries the Gouwe river over the A12 highway, which is on land below the level of the river
- Benjamin Outram's 44ft-long single-span Holmes Aqueduct on the Derby Canal in Derby was the world's first navigable cast iron aqueduct, narrowly predating Thomas Telford's 186ft-long Longdon-on-Tern Aqueduct on the Shrewsbury Canal, sometimes described as the world's first large-scale navigable cast iron aqueduct.
- the Pontcysyllte Aqueduct carries the Llangollen Canal over the River Dee in north Wales, and was designed by Thomas Telford and opened in 1805.
- the Union Canal in Scotland has many aqueducts, including the Slateford Aqueduct that takes the canal over the Water of Leith, the Almond Aqueduct over the River Almond at Ratho and the very impressive Avon Aqueduct over the River Avon. This is the second longest aqueduct in the United Kingdom.
- in recent years the building of the Lichfield Aqueduct prompted the UK government to pass legislation preventing a road being built in the path of a canal being renovated without providing a tunnel or aqueduct for it to pass.
- The Bridgewater Canal is carried across the lower Manchester Ship Canal by the Barton Swing Aqueduct - a form of swing bridge. A 234ft section of the aqueduct rotates through 90 degrees to allow vessels to pass along the Ship Canal.
- The Magdeburg Water Bridge in Germany connects the Elbe-Havel canal to the important Mittellandkanal. Nearly 1km long, it is the longest Water Bridge in Europe.

Ancient Greek aqueducts

- The Eupalinian aqueduct on the Greek island of Samos. An ancient subterranean aqueduct.

Roman aqueducts

Samos. Roman aqueduct.]] Samos, Turkey]]
- The Pont du Gard in southern France
- Barbegal aqueduct, France
- Eifel aqueduct, Germany
- Caesarea Palaestina, Israel
- Segovia, Spain
- Mérida, Spain
- Tarragona, Spain
- Valens aqueduct, Istanbul, Turkey
- Aqua Augusta, Italy

Other aqueducts

- Aqueduct of Teruel, Spain
- Central Arizona Project Aqueduct
- Chirk Aqueduct, Wales - built between 1796 and 1801
- Pontcysyllte Aqueduct, Wales - built between 1795 and 1805
- Roquefavour aqueduct, France - built between 1842 and 1847
- Aqueduct St-Clément, Montpellier, France - 17th century
- Winnipeg Aqueduct, Manitoba, Canada - built between 1913 and 1919

External links and references

- [http://aquaduct.hobbysite.info/ Everything about aqueducts]
- Sextus Iulius Frontinus, [http://www.uvm.edu/~rrodgers/Frontinus.html De Aquaeductu Urbis Romae] (On the water management of the city of Rome), Translated by R. H. Rodgers, 2003, University of Vermont
- [http://aquaduct.hobbysite.info/ Website about aqueducts]
- [http://www.waterhistory.org/histories/rome/ Imperial Rome Water Systems]
- [http://www.dl.ket.org/latin3/mores/aqua/rome.htm Roman Aqueducts Today]
- [http://encyclopedia.jrank.org/APO_ARN/AQUEDUCT_Lat_aqua_water_and_duc.html "Aqueduct"] from Encyclopedia Britannica 1911.
- [http://www.cs.uu.nl/~wilke/ 600 roman aqueducts with 25 descriptions in detail]
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Brick

This page is about bricks used for construction. For other types of brick please see Brick (disambiguation). Brick (disambiguation) A brick is a ceramic block made of kiln-fired material, usually clay or ground shale. Clay bricks are formed in a mould (the soft mud method), or more frequently in commercial mass production by extruding clay through a die and then wire-cutting them to the proper size (the stiff mud process). Brick made from dampened clay must be formed in molds with a great deal of pressure, usually applied by a hydraulic press. These bricks are known as hydraulic-pressed bricks, and have a dense surface which makes them highly resistant to weathering, and thus suitable for facing work. The shaped clay is then dried and fired to achieve the final, desired strength. In modern brickworks, this is usually done in a continuously fired kiln, in which the bricks move slowly through the kiln on conveyors, rails, or kiln cars to achieve consistent physical characteristics for all bricks. Bricks are also known in the building trades as compressed earth blocks or CEBs.

History

clay In the Near East and India, bricks have been in use for more than five thousand years. The Tigris-Euphrates plain lacks rocks and trees. Sumerian structures were thus built of plano-convex mudbricks, not fixed with mortar or with cement. As plano-convex bricks (being rounded) are somewhat unstable in behaviour, Sumerian bricklayers would lay a row of bricks perpendicular to the rest every few rows. They would fill the gaps with bitumen, straw, marsh reeds, and weeds. The Ancient Egyptians and the Indus Valley Civilization also used mudbrick extensively, as can be seen in the ruins of Buhen, Mohenjo-daro and Harappa, for example. The Romans made use of fired bricks, and the Roman legions, which operated mobile kilns, introduced bricks to many parts of the empire. Roman bricks are often stamped with the mark of the legion that supervised its production. The use of bricks in Southern and Western Germany, for example, can be traced back to traditions already described by the Roman architect Vitruvius. In the 12th century, bricks from Northern Italy were re-introduced to Northern Germany, where an independent tradition evolved. It culminated in the so-called brick Gothic, a reduced style of Gothic architecture that flourished in Northern Europe, especially in the regions around the Baltic Sea which are without natural rock resources. Brick Gothic buildings, which are built almost exclusively of bricks, are to be found in Denmark, Germany, Poland and Russia. However, bricks were long considered an inferior substitute for natural rock. During the Renaissance and the Baroque, visible brick walls were unpopular and the brickwork was often covered with plaster. It was only during the mid-18th century that visible brick walls regained some degree of popularity, as illustrated by the Dutch Quarter of Potsdam, for example.

Construction and types

Potsdam Hard-burned brick should be used for face work exposed to the weather, and soft brick for filling, foundations, and the like. The mainstay standard US brick measures approximately 8 x 4 x 2.25 inches (203 x 102 x 57 millimeters), and has a crushing strength of between 1000 and 3000 lbf/in² (7 to 21 megapascals) depending on quality. The standard UK brick size is 215 x 102.5 x 65 millimetres. A highly impervious and ornamental surface may be laid on brick either by salt glazing, in which salt is added during the burning process, or by the use of a "slip," which is a glaze material into which the bricks are dipped. Subsequent reheating in the kiln fuses the slip into a glazed surface integral with the brick base.

Proportions

Regardless of size, bricks are usually manufactured with the depth equal to half the length (assuming that the brick is laid horizontally). This allows for several convenient layouts which must necessarily interweave the bricks in any structure, often both at the corners and within the wall depth in order to ensure the greatest possible durability of the structure.

Use

salt glazing) on the west side of Lake Lily in Maitland, Florida. It was built in 1915 or 1916, paved over at some point, and restored in 1999.]] Bricks are typically for building. In the USA at one time, it was popular to pave roads with bricks, but they were found incapable of withstanding heavy traffic. Brick paving is again coming back into use as a method of traffic calming or as a decorative surface in pedestrian precincts. Bricks are also used in the metallurgy and glass industries for lining furnaces. They have various uses, especially refractory bricks such as silica, magnesia and neutral (chromomagnesite) refractory bricks. This type of brick must have a series of properties such as good thermal shock resistance, refractoriness under load, high melting point, satisfactory porosity (which can influence several other properties), all of which are high-temperature properties. There is a large refractory brick industry, especially in the United Kingdom, Japan and the U.S.A.

Mortar (masonry)

Mortar is a material used in masonry to fill the gaps between blocks in construction and bind the blocks together. The blocks may be stone, brick, breezeblocks (cinder blocks), etc. Mortar is a mixture of
- sand,
- a powdered adhesive such as cement,
- and water and is applied as a paste which then dries hard.

Gypsum mortar

The earliest known mortar was used by the ancient Egyptians and was made from gypsum. This form was essentially a mixture of plaster and sand and was quite soft.

Cement mortar

Cement mortar is created by mixing Pozzolana or Portland cement with sand and water and is harder than gypsum mortar. Though cement was first invented by the Egyptians (see cement), the first known use of cement mortar is found in the Roman Empire. However, the use of cement mortar did not become widespread in Europe until the 18th century and did not fully replace lime mortar until about 1930.

Lime mortar

Lime mortar is created by mixing sand and quicklime, or quicklime and cement mortar, and water. The earliest known use of lime mortar dates to about 4000 BC in Ancient Egypt. Lime mortars were used throughout the world, notably in Roman Empire buildings throughout Europe and Africa. Quicklime is made by the following simple process: :CaCO₃ + heat → CaO + CO₂. #Calcination: heat limestone or marble, both of which contain primarily calcium carbonate (CaCO₃), to 900°C. #The excessive heat then causes carbon dioxide, CO₂, to be released as a gas. #The result is quicklime, CaO (calcium oxide). When the quicklime is then mixed with water it forms calcium hydroxide (Ca(OH)₂), also called hydrated or slaked lime. As the mixture dries the slaked lime reacts with atmospheric carbon dioxide (CO₂) to form back into solid calcium carbonate (CaCO₃), releasing yet more (evaporating) water in the process. Though slaked lime is normally fairly plastic and easy to work with, it is nevertheless toxic with overexposure (see slaked lime). Lime mortar dries very slowly. In some buildings, lime mortar made of quicklime and sand alone may take several years or even decades to completely solidify [http://www.americanscientist.org/template/AssetDetail/assetid/17236/page/3] as this process relies solely on the re-absorption of atmospheric carbon dioxide back in the mortar to form calcium carbonate. Even when quicklime is mixed with cement, the same properties still hold; though it may seem to dry faster (because of the quicker-drying cement present). Nevertheless, limestone-free cement mortar is not as strong as lime mortar (see cement). Analogous to the greater strength and lower porosity associated with modern Pozzolana mortar when compared with Portland mortar alone (see Pozzolana), lime mortar is stronger than cement mortar alone (see cement). This is because the components of slaked lime and slag (both consisting primarily of calcium) act analogously as the silicates and alumina -- in the form of silica fume and the primary component of fly ash -- that are added to modern cement mortars ([http://www.americanscientist.org/template/AssetDetail/assetid/17236/page/5]) to create a stronger mortar. Note too that Portland cement used today already contains finely ground limestone for some added strength. Lime mortar was an integral part of how traditional buildings "worked". Lime mortar, unlike cement mortar, is porous. Water entering walls from the ground or above could escape through the mortar, rather than leaving the wall waterlogged, which would lead to increased dampness inside. Many old buildings have been damaged by being repointed in modern harder cements, which are not porous and change the water handling profile in an undesirable way. Lime mortar is also more flexible than Portland cement, so building movement is less likely to crack the mortar. Traditional buildings lack the expansion joints found in modern buildings. Because lime mortar is slow-drying and slightly more hazardous to work with, it is less often used for new buildings, which take a different approach to damp prevention. The strength of many walls made today with modern bricks derives primarily from the stronger bricks.

Dating lime mortar

Because lime mortar absorbs atmospheric carbon dioxide as it dries, samples of lime mortar taken at archaeological sites may be carbon-dated to determine approximate age. See [http://www.americanscientist.org/template/AssetDetail/assetid/17236/page/2 American Scientist: Dating Ancient Mortar].

Pozzolana mortar

See Pozzolana.

Inca

: For other meanings of Inca, see Inca (disambiguation).