Bridge (redirected from bridgework)

bridge, structure

bridge, structure built over water or any obstacle or depression to allow the passage of pedestrians or vehicles. See also viaduct.

Early Bridges

In ancient times and among primitive peoples a log was thrown across a stream, or two vines or woven fibrous ropes (the upper for a handhold and the lower for a footwalk) were thrown across, to serve as a bridge. Later, arched structures of stone or brick were used; traces of these, built from 4000 to 2000 B.C., have been found in the E Mediterranean region. The Romans built long, arched spans, many of which are still standing. Bridges built during the Middle Ages usually rested on crude stone arches with heavy piers (intermediate supports) that were a great obstruction to river traffic, and their roadways were often lined with small shops.

The best known early American design is the New England covered bridge, since wood was abundant and cheap, and did not demand trained masons. Colonial American bridge builders were willing to run the risk of rot or fire in exchange for such savings in time and manpower. Beginning with Abraham Darby's bridge at Coalbrookdale in 1779, most bridges began to be built of cast and wrought iron. Robert Stephenson, an English engineer, designed and built a bridge of this type across Menai Strait in North Wales (1850). Another is Victoria Bridge across the St. Lawrence at Montreal. The disadvantage of cast iron for bridges is its low tensile strength.

Modern Bridge Designs

There are six basic modern bridge forms: the beam, the truss, the arch, the cantilever, the cable-stay, and the suspension. A beam bridge is made of long timber, metal, or concrete beams anchored at each end. If the beams are arranged in a lattice, such as a triangle, so that each shares only a portion of the weight on any part of the structure, the result is a truss bridge. An arch bridge has a bowed shape causing the vertical force of the weight it carries to produce a horizontal outward force at its ends. It may be constructed of steel, concrete, or masonry. A cantilever bridge is formed by self-supporting arms anchored at and projecting toward one another from the ends; they meet in the middle of the span where they are connected together or support a third member. In a cable-stayed bridge, the roadway is supported by cables attached directly to the supporting tower or towers. This differs from a suspension bridge, where the roadway is suspended from vertical cables that are in turn attached to two or more main cables. These main cables hang from two towers and have their ends anchored in bedrock or concrete.

The modern era of bridge building began with the development of the Bessemer process for converting cast iron into steel. It became possible to design framed structures with greater ease and flexibility. Single-piece, rolled steel beams can support spans of 50 to 100 ft (15–30 m), depending on the load. Larger, built-up beams are made for longer spans; a steel box-beam bridge with an 850-ft (260-m) span crosses the Rhine at Cologne.

Truss, Arch, and Cantilever Bridges

The truss can span even greater distances and carry heavy loads; it is therefore commonly used for railroad bridges. A large truss span like that over the Columbia River at Astoria, Oreg., can extend to 1,232 ft (376 m). If the truss is shaped into an arch, even longer bridges are possible; the Bayonne Bridge between New York and New Jersey, the Sydney Harbor Bridge in Australia, and the New River Bridge in West Virginia are the longest steel arch bridges, at 1,675 ft (510 m), 1,670 ft (509 m), and 1,700 ft (518 m), respectively. Concrete arch bridges tend to be somewhat smaller, the largest being the Krk Bridge in Croatia and the Gladesville Bridge across the Parramatta River at Sidney, Australia, at 1,280 ft (390 m) and 1,000 ft (305 m), respectively; the longest concrete arch bridge in the United States is the Natchez Trace Parkway Bridge in Franklin, Tenn., at 582 ft (177 m). The cantilever, however, is more common for spans of such lengths. The cantilevered Forth Bridge (1890) in Scotland was the first major structure built entirely of steel, the material that made possible its two record-setting spans of 1,710 ft (521 m) each. They remained the longest in existence until 1917, when the St. Lawrence River at Quebec Bridge was built; it has an 1,800-ft (549-m) span. The longest cantilever bridge in the United States is the Commodore John Barry Bridge in Chester, Penn., which has an 1,644 ft (501 m) span.

Cable-Stayed, Suspension, and Combination Bridges

The cable-stayed bridge is the most modern type, coming into prominence during the 1950s. The longest is the Tatara Bridge in Ehime, Japan, which has a 2,920 ft (890 m) span. The Ponte de Normandie in Le Havre, France, spans 2,808 ft (856 m); the Second Yangtze Bridge in Nanjing, China, spans 2,060 ft (628 m); and the Third Yangtze Bridge in Wuhan, China, spans 2,028 ft (618 m). The longest cable-stayed bridge in the United States is the Dame Point Bridge in Jacksonville, Fla., which has a span of 1,300 ft (396 m).

The suspension bridge is used for the longest spans. The earliest suspension bridges built in America were those constructed by the American builder James Finley. The design of suspension bridges advanced when J. A. Roebling, a German-born engineer who emigrated to the United States, developed the use of wire cables and stiffening trusses. His first completed suspension bridge spanned the Niagara River in 1854. He also designed the Brooklyn Bridge across the East River (completed 1883), which was the world's longest suspension bridge at the time of its construction, having a main span of 1,595.5 ft (487 m).

Today the longest spans in the world are suspended. The longest main spans are the Akashi Kaikyo Bridge, Hyogo, Japan, 6,529 ft (1,990 m); Izmit Bay Bridge, Marmara Sea, Turkey, 5,472 ft (1,668 m); Store Bælt Bridge, Denmark, 5,328 ft (1,624 m); Humber River Bridge, Hull, England, 4,626 ft (1410 m); Tsing Ma Bridge, Hong Kong, 4,518 ft (1,377 m); Verrazano-Narrows Bridge, New York City, 4,260 ft (1,298 m); Golden Gate Bridge, San Francisco, 4,200 ft (1,280 m); Hoga Kusten (or High Coast) Bridge, Västernörrland, Sweden, 3,969 ft (1,210 m); Mackinac Straits Bridge, Mich., 3,800 ft (1,158 m); Minami Bisan-Seto Bridge, Japan, 3,668 ft (1,118 m); Second Bosporus Bridge, İstanbul, Turkey, 3,576 ft (1,090 m); First Bosporus Bridge, İstanbul, Turkey, 3,524 ft (1,074 m); and George Washington Bridge, New York City, 3,500 ft (1,067 m).

Combination spans are often used to bridge even longer stretches of water. The San Francisco–Oakland Bay Bridge, noted for its three long spans, of which two are suspension spans and the third a cantilever, has a total length of 8.25 mi (13.2 km). The Chesapeake Bay Bridge-Tunnel has two 1-mi (1.6-km) tunnels along its 17.6-mi (28.2-km) length, and the 8-mi (12.9-km) Confederation Bridge, linking Prince Edward Island to the Canadian mainland, consists of three bridges. The longest combination spans are the twin Lake Ponchartrain Causeways near New Orleans, Louisiana, whose parallel roadways stretch nearly 24 mi (38 km).

Movable Bridges

Movable bridges are generally constructed over waterways where it is impossible or prohibitive to build a fixed bridge high enough for water traffic to pass under it. The most common types of movable bridge are the lifting, bascule, and swing bridges. The lifting bridge, or lift bridge, consists of a rigid frame carrying the road and resting abutments, over each of which rises a steel-frame tower. The center span, which in existing bridges is as long as 585 ft (178 m), is hoisted vertically. The bascule bridge follows the principle of the ancient drawbridge. It may be in one span or in two halves meeting at the center. It consists of a rigid structure mounted at the abutment on a horizontal shaft, about which it swings in a vertical arc. The lower center span of the famous Tower Bridge in London is of the double-leaf bascule type. Because of the need for large counterweights and the stress on hoisting machinery, bascule bridge spans are limited to about 250 ft (75 m). The swing bridge is usually mounted on a pier in midstream and swung parallel to the stream to allow water passage.

Military Bridges

In wartime, where the means of crossing a stream or river is lacking or a bridge has been destroyed by the enemy, the military bridge plays a vital role. Standard types of military bridges include the trestle, built on the spot by the engineering corps from any available material, and the floating bridge made with portable pontoons.

Bibliography

See D. Plowden, The Spans of North America (1984); H. Petroski, Engineers of Dreams: Great Bridge Builders and the Spanning of America (1995); J. Dupré and F. O. Geary, Bridges: A History of the World's Most Famous and Important Spans (1996); S. A. Ostrow, Bridges (1997); F. Gottemoeller, Bridgescape: The Art of Designing Bridges (1998); K. Willard, Bridges: Designing the Future (1999). See also bibliographies for articles on individual bridges.

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bridge, card game

bridge, card game derived from whist, played with 52 cards by four players in two partnerships.

Basic Rules

The cards in contract bridge rank from ace down to two; in bidding, suits rank spades, hearts, diamonds, and clubs. After all cards are dealt, so that each player holds 13 cards, the dealer begins the auction, which proceeds in rotation to the left. Each player must bid, pass, double (increase the value of the previously stated contract), or redouble (only after a double, further increasing the point value of the contract). A bid is an offer to win a stated number (over six) of tricks with a named suit as trump or with no trump. The lowest bid is one, the highest seven. Each bid, i.e., "one diamond," "one no-trump," "four hearts," must be higher than the preceding bid, with no-trump ranking above spades. Artificial bids are those that convey certain information to a partner and are not meant to be taken literally. The highest bid of the auction becomes the contract after three consecutive passes end the bidding. The player who first named the suit (or no-trump) specified in the winning bid becomes the declarer. The player to the left of the declarer leads any card face up, and the next hand, that of the declarer's partner, is placed face up on the table, grouped in suits. This is known as the dummy, and the declarer selects the cards to be played from this hand. The object of the game for both partnerships is to win as many tricks as possible, a trick being the three cards played in rotation after the lead. Suits must be followed, but a player who has no cards in the suit led may play any card. Highest trump or, if no trump card is played, highest card of the suit led wins. Points are awarded for the number of tricks won. Numerous conventions—generally accepted forms of bidding—are used in bridge, but the four standard ones are Blackwood, Gerber, Stayman, and grand-slam force.

Competitive Bridge

Duplicate bridge, in which the same prearranged hands are played by individuals, pairs, or teams of four, is the main form of competitive bridge. The laws of contract bridge are promulgated in the Western Hemisphere by the American Contract Bridge League, which holds various bridge tournaments. In international contract bridge matches the Bermuda bowl, the trophy for victory, is the emblem of the world championship. In Olympic years an olympiad championship is held by the World Bridge Federation and replaces the team tournament for the Bermuda bowl.

History

Bridge probably originated in the Middle East in the 19th cent. Auction bridge, one form of the game, was developed by the British in India and later was popular in England and the United States. It is still played but has largely been supplanted by contract bridge, which achieved popularity after important innovations were made in 1925 by Harold S. Vanderbilt. Its phenomenal popularity owed much to the activities of Ely Culbertson. The craze subsided but was later revived; books, tournaments, and newspaper columns on bridge abound. Culbertson devised the honor count system to evaluate a hand for bidding. The point count (or standard American) system introduced by Charles H. Goren in the 1940s has generally replaced honor count.

Bibliography

See C. H. Goren, Bridge Complete (rev. ed. 1971); T. Reese and A. Dormer, The Complete Book of Bridge (1974).

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bridge

Three common types of bridge design.

(credit: © Merriam-Webster Inc.)

Structure that spans horizontally to allow pedestrians and vehicles to cross a void. Bridge construction has always presented civil engineering with its greatest challenges. The simplest bridge is the beam (or girder) bridge, consisting of straight, rigid beams of steel or concrete placed across a span. Ancient Roman bridges are famous for their rounded arch form, which permitted spans much longer than those of stone beams and were more durable than wood. A modern version of the arch bridge might have a trussed arch anchored to the abutments and a deck hanging from the arch by vertical cables. Suspension bridges (e.g., Brooklyn Bridge, Golden Gate Bridge) are capable of spanning great distances; their main support members are cables composed of thousands of strands of wire supported by two towers and anchored at each end, and the deck is suspended by vertical cables hung from the main cables. In cable-stayed bridges, cables fan out and down from a central tower to various points on the deck; variations of this design have resulted in bridges of striking design and very long span. Other bridges include the truss bridge, popular (e.g., for railroad bridges) because it uses a relatively small amount of material to carry large loads, and the cantilever bridge, typically made with three spans, with the outer spans anchored down at the shore and the central span resting on the cantilevered arms.

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bridge

Card game similar to whist. Bridge is any one of several games, including games such as auction bridge and contract bridge, which retain the essential features of whist: Four players participate, two against two in partnership. They play with a 52-card pack, all cards of which are dealt face downward one at a time, clockwise. When play begins, the object is to win tricks, consisting of one card from each player in rotation. The players must, if able, contribute a card of the suit led, and the trick is won by the highest card. All tricks taken in excess of the first six tricks are known as odd tricks. Before play begins, a suit may be designated the trump suit, in which case any card in it beats any card of the other suits. In all types of bridge a certain number points are needed to win a game, and two games won by the same team allows them to win the rubber.

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(1) To cross from one circuit, channel or element over to another.

(2) See Wi-Fi bridge and wireless bridge.

(3) A device that connects two LAN segments together, which may be similar or dissimilar, such as Ethernet and Token Ring. A bridge is inserted in the network to keep traffic contained within the segments to improve performance. By monitoring which station acknowledged receipt of the address, bridges learn which nodes belong to the segment and maintain their own address tables. Multiport bridges have more than two ports and perform a switching function just like a LAN switch.

Bridges Vs. Routers
Bridges work at layer 2 and are not protocol dependent. Routers work at layer 3 and are protocol dependent. Bridges are faster than routers because they do not have to glean routing information. See LAN, transparent bridge, repeater, router, gateway and hub. See also conference bridge.

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Bridge

Al Sirat

fine as razor’s edge, over which all must pass to enter paradise. [Islam: Koran]

Amaurote

Utopian crossing; means “faintly seen.” [Br. Lit.: Utopia]

Bifrost

rainbow of water and fire for gods’ passage from Asgard to Midgard. [Norse Myth.: Leach, 139]

Bridge of San Luis Rey

rope bridge in Andes which breaks, killing five people. [Am. Lit.: Bridge of San Luis Rey]

Brooklyn Bridge

suspension bridge spanning the East River from Manhattan to Brooklyn. [Am. Hist.: EB, II: 301]

Golden Gate Bridge

suspension bridge in San Francisco spanning the Golden Gate. [Am. Hist.: EB, IV: 607]

London Bridge

a bridge spanning the Thames at London; (not the Tower Bridge). [Br. Hist.: EB, VI: 311]

River Kwai Bridge

bridge built by British POWs under Japanese orders. [Jap. Hist.: Bridge Over the River Kwai]

Xerxes

constructed famed pontoon crossing of Hellespont. [Gk. Hist.: Brewer Dictionary, 1169]

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1.		BRIDGE - A component of ICES for civil engineers. [Sammet 1969, p. 616].
2.	(networking, hardware)	bridge - A device which forwards traffic between network segments based on data link layer information. These segments would have a common network layer address. Every network should only have one root bridge. See also gateway, router.