. The elements of railroad engineering . nd uniform groove or projection. 1475. Centers for Arches.—A center is a temporarywooden structure for supporting an arch while it is beingbuilt. Centers are built lying flat on a fixed platform, to afull-sized drawing, and vary widely in design, according tothe type and dimensions of the arch. The different parts ofa center are given in Fig. 393, which is a standard type ofcentering for all arches of moderate span, say from 6 to 16 feet. 894 RAILROAD CONSTRUCTION. The frames A, A are made of ribs of H-inch plank andunited as shown in the figure, breaki
. The elements of railroad engineering . nd uniform groove or projection. 1475. Centers for Arches.—A center is a temporarywooden structure for supporting an arch while it is beingbuilt. Centers are built lying flat on a fixed platform, to afull-sized drawing, and vary widely in design, according tothe type and dimensions of the arch. The different parts ofa center are given in Fig. 393, which is a standard type ofcentering for all arches of moderate span, say from 6 to 16 feet. 894 RAILROAD CONSTRUCTION. The frames A, A are made of ribs of H-inch plank andunited as shown in the figure, breaking joints and fastenedtogether with spikes. The ribs are fitted to the drawing asthe frames are built. The ribs are 4 ft. 1 in. in length, 8 width at ends, and 10 in. in width at middle, the edgebeing trimmed down to fit the curve of the arch. The chord7) is composed of two planks, each H in. thick by 10 in. inwidth and 1(5 ft. in length, spiked securely to the upright strut C is 3 in. thick by 10 in. in width, placed. directly under the crown of the arch and fastened to theframe by two cleats D securely spiked to both frame andstrut. Its foot passes between the planks forming the chordto which it is spiked. The brace £ is fastened at top to thestrut with spikes. Its foot passes between the chord planksand is shaped to abut against the rib at the spring line,being securely spiked to the chord. The frames are spaced3 feet from center to center, and rest on G in. by G in. caps/ which are supported by 6 in. by G in. posts G. These postsrest on 4 in. by 6 in. ground sills // which rest on the stonepaving. On the caps directly under each frame are strikingor lowering wedges K, by means of which the frames areraised in case any of the posts should settle. RAILROAD CONSTRUCTION. 895 1476. Striking Centers.—Upon the completion ofthe masonry, the lowering wedges are removed, which per-mits of the removal of the centering. This process is calledstriking the centers.
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectrailroadengineering
