File:A treatise on concrete, plain and reinforced - materials, construction, and design of concrete and reinforced concrete; 2nd ed. (1912) (14597039649).jpg

Identifier: treatiseonconcr00tayl (find matches)
Title: A treatise on concrete, plain and reinforced : materials, construction, and design of concrete and reinforced concrete; 2nd ed.
Year: 1912 (1910s)
Authors: Taylor, Frederick Winslow, 1856-1915 Feret, R Thompson, Sanford E. (Sanford Eleazer), b. 1867
Subjects: Concrete Reinforced concrete
Publisher: New York : J. Wiley
Contributing Library: Robarts - University of Toronto
Digitizing Sponsor: University of Toronto

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centering is easily lowered. The ribs of the centering are usually made of several pieces of plankspiked or bolted together. Upon the ribs rests the lagging, which usuallyconsists of one or two layers of planking having the top surface smoothedto give a good surface to the soffit of the arch, and laid with tight joints.With thin lagging care must be taken to prevent deflection. Instead of the ribs forming a part of the truss, they are frequently sup-ported directly upon the wedges resting upon the caps of the bents, theposts of which run up to the soffit of the arch for that purpose. The centering should be cambered, that is, should be made higher thancalled for in the arch plans at the center, so that when it is removed, the archwill be in the position assumed for it in the design. Some engineers make ^Engineering News, Aug. 30, 1906, p. 215. tJournal Association of Engineering Societies, July 1901, p. 10. For examples of center-,built in various places, see References, Chapter XXXI.
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590 A TREATISE ON CONCRETE the camber equal to the deflection of the arch which would be caused bythe live and dead loads. In striking the centers sudden settlement must be avoided and the cen-ters must not be removed until the concrete has attained good strength.The time of removal must be determined by the design of the bridge andthe weather. For light highway bridges four weeks is usually suffi-cient, while for a heavy arch of long span eight weeks may be required. EXAMPLES OF ARCH BRIDGES Mystic River Bridge, Medford, Mass. This arch, illustrated inFig. 183, page 589, is of the Monier type and carries a parkway over theriver. It was built in 1906 by the Metropohtan Park Commission, Mr.John R. Rablin, Chief Engineer. The arch has a span of 60 feet, a rise of 8 feet, and a crown thicknessof 18 inches. Both the intrados and the extrados are segmental. The sidewalls are of concrete with a vertical expansion joint at each abutment.The retaining wall for the earth fill over the abutment

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