The elasticity and resistance of the materials of engineering . he method of designing such a beam, and the calculationof the elements of its resistance, will be given in detail. Thebeam is supposed to be of wrought iron, and one of a systemfor a double track railway bridge ; the stringers under the twotracks, which rest on the beam, are placed at A and B, and Dand //. The weight of the beam, taken uniformly distributed,IS 5, pounds. The concentrated load at each of thepoints A, B, D and //, composed of the train weight added tothat oi the stringers, is 42, pounds. Art. 66,] DATA.
The elasticity and resistance of the materials of engineering . he method of designing such a beam, and the calculationof the elements of its resistance, will be given in detail. Thebeam is supposed to be of wrought iron, and one of a systemfor a double track railway bridge ; the stringers under the twotracks, which rest on the beam, are placed at A and B, and Dand //. The weight of the beam, taken uniformly distributed,IS 5, pounds. The concentrated load at each of thepoints A, B, D and //, composed of the train weight added tothat oi the stringers, is 42, pounds. Art. 66,] DATA. 579 The following are some of the dimensions of the beam: Span RR = feet. Depth of web plate = 36 = feet. nH = AB = feet. BB = The web plate will be taken j\ inch thick. The method ofdetermining this thickness will be shown hereafter. In this case resistance to flexure of the web will be neg-lected ; ^/le web will be assumed to resist the shear 07tly, as isassumed in Eqs. (7) and (/a) of Art. 65. The ** depth, d^, of the. beam will then be the vertical distance between the centres ofgravity of the sections of the flanges, and each flange is to beconsidered as composed of two Ls and the ** cover* plate orplates only; no part of the web is to be included. Strictlyspeaking, then, the depth is variable ; but this variation is soslight that no essential error will be committed if it be con-sidered constant and equal to the depth of web plate, or 36inches. This procedure, which saves much labor and time, isalways permissible where cover plates are used. The next ex-ample will exhibit a case in which they are not used. TJie direct stresses of tension and compression existing in theflanges must be carried through the rivets which unite the flangesto the zueb; hence the necessary number of those rivets willfirst be determined. The reaction at R, using the data already given, will be: R = 2 X 42, -f- ——-— = 86, pounds. 5So BU
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