. The elements of railroad engineering . Fig. 387. DFE and G B H \?> called the face. Lines level with Dand E and at right angles to the face of the arch are calledspringing lines or springs. The blocks of which thearch is composed are called arch stones or center one B F is the keystone, and the lowest onesA and C the springers. The parts B G and B H are thehaunches. The spaces BG N K and B HML are thespandrels. The material deposited in these spaces isthe spandrel filling. It is sometimes earth and sometimesmasonry or partly of both. Arches according to their forms have diff
. The elements of railroad engineering . Fig. 387. DFE and G B H \?> called the face. Lines level with Dand E and at right angles to the face of the arch are calledspringing lines or springs. The blocks of which thearch is composed are called arch stones or center one B F is the keystone, and the lowest onesA and C the springers. The parts B G and B H are thehaunches. The spaces BG N K and B HML are thespandrels. The material deposited in these spaces isthe spandrel filling. It is sometimes earth and sometimesmasonry or partly of both. Arches according to their forms have different names. RAILROAD CONSTRUCTION. 887 That in Fig. 387 is a semicircular arch, and is the formcommonly adopted in culvert building. A circular archcontaining an arc of less than 180° is called a segmentalarcli (see Fig. 388). The arch shown in Fig. 380, composed. Fig. 388. Fig. 389. of three circular arcs, is called either an elliptical or athree-centered arch. 1469. To Find the Depth of Keystone.—For cutstone arches, whether circular or elliptic, find the radius O D^Figs. 387, 388, and 389, which will touch the arch at D, F,and E. Rule I-—Add together this radius and half the span D tJie square root of the sit in. Divide this square root by add to the quotient -^^ of a foot. Or, by formula, depth of keystone in feet = l^^^Z±S£« + ..,y,„,. (,o3.) 4- Eor second-class zvork, increase this depth of keystone about^ part; for brickzvork or fair rubble., about \ part. Example.—The radius C?/? is 18 feet, the span Z> £ 36 feet; required,the depth of an arch of cut stone for second-class work and for brick-work. Solution.—Applying formula 103, we have y 18 + 18For cut stone, depth of arch = ■ r +.2 foot = feet. Ans. 888 RAILROAD CONSTRUCTION. For second-class work, increase depth of cut stone arch-| = 4-i X 17
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectrailroadengineering
