Page:The New International Encyclopædia 1st ed. v. 03.djvu/561

* BRIDGE. 489 BRIDGE. which is the gorge of the Niagara River. In these cases the engineer must use a single long span, and is, therefore, restricted to the types of bridge which will permit great length of clear span, such as the metal arch, the cantilever truss, or the suspension types. In other instances the handsome appearance of the bridge is paramount, and some design which will fulfill this require- ment is necessary. If a navigable stream is to be crossed at low level, a drawbridge is nccessarj-. Thus it will be seen that the local conditions and requirements have to be most carefully stud- ied, and the available designs in each case care- fully integrated, to secure the one which will best meet the controlling conditions at the low- est cost. The design once selected, the engineer, knowing the loads which the bridge is to carry, proceeds to calculate the character and intensity of the strain in each principal member. This being done and the strength of the material known, it is possible to determine the size re- quired of each member to resist the strain coming upon it. The next process is to determine the form and dimensions of each member and to pre- pare drawings showing closely the form and these dimensions. As soon as the detail drawings have been pre- pared, the engineer draws up a set of specifica- tions stating the location, purpose, and main di- mensions of the bridge, the character and strength of the material to be used in each part, the quality of workmanship required in constructing and erecting these parts, and a variety of other stipulations tending to secure in the finished structure the embodiment of his intentions as regards the finished bridge. The detail drawings and the specifications are then submitted to bridge-builders with the request that they make bids for performing the required work. Gener- ally the lowest bid is accepted, providing the engineer is satisfied of the reliability and com- petency of the person making it to perform the work. After the contract has been let, the bridge- maker receiving it begins the manufacture of the bridge. First wooden templates and models ure made from the engineer's drawing of at least the most important members. These are used for marking the shape and dimensions to which the steel is to be cut, and in molding the castings. The steel, being marked, is cut to the required dimensions and forms by shears and planers. Each piece is then sent to the punches, drills, and boring-machines to have the rivet and pin holes bored. The next step is to assemble the pieces forming each member and fasten them together by tcmporarj' pins. The assembled member is then taken to the riveting-machines, which drive the p<'rmanent rivets. The next step is to finish the member, mark it with its dis- tinctive number, and load it for shipment. The attempt is always made to ship the metal-work in as large sections as possible, since the con- nections made at the bridge-shops equipped with special machinery for the purpose are more solid and cheaper than those made in the field by portable machinery. At best, however, the bridge material reaches the site of the bridge in a great numljer of pieces, and the work of con- necting these pieces to form the completed bridge is called bridge erection. Metal bridges are usually erected on a supporting falsework of timber, but where such a falsework is impracti- cable they arc built out from one or both ends piece by piece, where the type of structure per- mits, or are erected on falsework standing on barges which are floated into the proper position to place the complete span on its piers by lower- ing it onto its .seats and withdrawing the barge. After erection, the bridge is painted and other- wise finished, and finally is commonly tested by running a very heavy load over it. The testing finishes tlic biidge so far as the bridge engi- neer is concerned. For pontoon and other forms of military bridges, see Bridges .xd Docks, lIlLIT.VRT. BiBLiOGBAPUT. The literature on bridge-build- ing is quite extensive and is widelj' scattered, much of the most valuable descriptive matter being found in the periodical literature of the engineering profession. Among engineering papers whose columns contain particularly full records of current bridge construction are: Le Genie Civil (Paris, 1880, current) ; Zeitschrift dcx ^'rrriy|.<! DciitsicJirr Inqcnirurr (Berlin. 18.57, current) : E»(]inrcring (London, 1866. weekly, current): Enpinccriiuj .Aries (Xew York, cur- rent) ; and the Engineering Record (Xew York, current). The Proceedings of the Institution of Ciril Engineers (London, 1838, current) ; Annates dcs Fonts et Chaussees (Paris, 1831, current) ; and Transactions American Society of Cii-il Engineers (Xew Y'ork, 1868, current), also contain much important information relating to bridges. Among the more recent text-books and books of reference are: Johnson, Practice of Modern Framed Structures (Xew York, 1900) ; Du Bois, Stresses in Framed Structures (Xew York, 1896) ; Merriman and Jacobv, Roofs and Bridges (Xew Y'ork, 1900) ; Waddell, De Ponti- bus (Xew York, 1898); Wright, The Designiyig of Drair Sjtans (Xew Y'ork, 1897). BRIDGE, OF A Ship. A platform raised some distance above the deck of a vessel for the con- venience of the olficer having charge of the deck. In modern men-of-war there are usually two bridges extending athwartship and a fore-and- aft bridge between them. The forward thwart- ship bridge is the one used for purposes of navi- gation, and it is usually placed ten feel or more above the upper deck. When the bridge expands into a platform of considerable area instead of being merely a narrow promenade, it is frequent- ly called a hridge-decl; . In very large ships there are usually two or three bridges, one above the other; in which case the lower ones are generally larger, and are called the upper and lower bridge decks. BRIDGE. A game of cards. It maj' be said to Ix'liing to the whist family of games, although in its recent development there is no direct rela- tionship. It has been played for some time in Turkey and Egpt. in which latter country it is known as Khrdirc. but in neither land is it ])layed so scientifically or with the same details as in England and .America. . game closely re- sembling bridge is plajed also in Holland, and still another in Russia, where it is known under the name of Veralash. Toward the end of the Xineteenth Century it traveled from Egypt to the south of France, whence it rapidly made its way to Paris and. although meeting with the opposition of whist-players, soon intrenched itself securely in the public estimation. London and Xew York followed Paris in their devotion to the new game. Bridge is jjlayed with one pack of