File:Revision of the Niagara Railway Arch Bridge (1920) (14760065326).jpg

Identifier: revisionofniagar00char (find matches)
Title: Revision of the Niagara Railway Arch Bridge
Year: 1920 (1920s)
Authors: Charles Evan Fowler
Subjects: Bridges
Publisher: (New York) : American Society of Civil Engineers
Contributing Library: Brock University
Digitizing Sponsor: Brock University - University of Toronto Libraries

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f the live loadfrom the opposite track, as only two toggles were used at a time andplaced on the posts of the trusses adjacent to the abandoned track. Thefitting up bolts had to be loosened before the toggles were tightened,and drawn up again just before riveting began, to give proper adjust-ment. The eight counters in the 115-ft. spans were replaced withU-counters having double the section, and the new rods were set withthe strain gauge to have an initial tension of about 3 000 lb. per sq. in. The greatest value of the strain gauge in the practical work on thearch revision was, of course, the checking up of the actual dead loadstresses, which, on account of the introduction of the adjusting shims,did not agree with the theoretical stresses; an accurate checking of thedistribution of stress over the cross-section of built tension and com-pression members; the checking of secondary stress; and the effect ofimpact at varying speeds. REVISION OF NIAGARA RAILWAY ARCH BRIDGE 1955 192 Panel
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Fig. 13.—Toggle Applied to Post of 115-Ft. Teuss. 195c revision of niagara railway arch bridge Unit Stresses. The fact has been recognized for some time that for heavy, special,and long-span bridges, the Profession is no longer warranted in usingthe low values for unit stresses that are prevalent for less importantshorter spans in which the secondary stress and closely accurate impactstresses have not been calculated or determined. Some authoritiesbelieve that where all stresses have been taken into account, unitstresses closely approaching the elastic limit should be used, with aloading that is quite sure not to be exceeded during the life of thestructure, such as Coopers E-90 loading or one similar to the com-posite loading proposed in this paper. The fact remains, however, that there are still some uncertaintiesas to the uniformity of the elastic limit and the ultimate strength ofmaterials, be they steel or steel alloys, as to the exact amount to beallowed for impact and vibratio

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