. Handbook of railroad construction; for the use of American engineers. Containing the necessary rules, tables, and formulæ for the location, construction, equipment, and management of railroads, as built in the United States .. . of a top and bottomchord connected by a vertical web. The whole being ofwrought iron, requires that the section of the upper chordshould be to that of the lower, as ninety to sixty-six. The general plan of such bridges is shown in fig. is the patent wrought iron girder bridge of Mr. Fair-bairn. The upper chord is formed by connecting the fourplates oaaa, by
. Handbook of railroad construction; for the use of American engineers. Containing the necessary rules, tables, and formulæ for the location, construction, equipment, and management of railroads, as built in the United States .. . of a top and bottomchord connected by a vertical web. The whole being ofwrought iron, requires that the section of the upper chordshould be to that of the lower, as ninety to sixty-six. The general plan of such bridges is shown in fig. is the patent wrought iron girder bridge of Mr. Fair-bairn. The upper chord is formed by connecting the fourplates oaaa, by angle irons. The web is formed either bya single or a double plate, stiffened laterally by T iron placedat the vertical plate joints, as shown generally at B, anddetailed at C and D; or by a pair of plates separated by aspace as at B, thus forming a rectangular tube. The lowerchord is made by bending horizontally the lower part of theweb, and to the flanges thus formed riveting the plate m suspending rod // is applied to the upper chord by awasher as at E. The central connecting web, acting as do the braces andties in a wooden truss, should be more stiff at the ends of ^24 HANDBOOK OF RAILROAD CONSTRUCTION. lig. IRON BRIDGES. 225 the span than at the centre. This is easily effected byjoining the web plates towards the end by stronger T ironsthan at the centre. The joints for the rib, or the verticalplates, either single or double, are shown in figs. C and D. An example of the need of such increased stiflhess towardsthe ends, was given to the experimenters upon the Britanniamodel tube, which (tube) was found to yield by bucklingnear the ends of the span sooner than elsewhere. Thusadvised, the vertical plates were made thicker as the end ofthe span was approached. Examination of the principlesof proportioning a common wooden truss would have shownthis without experiment. The tensile and compressive strength of rolled boilerplates (by the table on page 194,) is, exten
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