. Railway mechanical engineer . he fact that one-half of the total load was as-sumed to act at either side bearing, irrespective of how farapart they were spaced. April. 1918 RAILWAY MECHANICAL ENGINEER 213 Bending moment diagrams have now been developed forspecifications which call for a system of loading whereinthe entire load is concentrated at the bolster center plate andalso for those specifications which provide that the load shallbe concentrated at the center plate or divided equally be-tween the center plate and one side bearing. With respectto the latter case, three different side bea
. Railway mechanical engineer . he fact that one-half of the total load was as-sumed to act at either side bearing, irrespective of how farapart they were spaced. April. 1918 RAILWAY MECHANICAL ENGINEER 213 Bending moment diagrams have now been developed forspecifications which call for a system of loading whereinthe entire load is concentrated at the bolster center plate andalso for those specifications which provide that the load shallbe concentrated at the center plate or divided equally be-tween the center plate and one side bearing. With respectto the latter case, three different side bearing spacings havebeen used in order to bring out the effect upon the bendingmoment due to differences in the spread of the side bear-ings, and to emphasize this point as regards its effect uponthe form of diagrams 5, 6 and 7, and to provide for a readycomparison, all three diagrams have been reproduced inFig. 2. Another type of bolster specification is one in which it isrequired that the bolster shall be designed for a certain. given section modulus (Z). The formula given in Fig. 3and developed by W. F. Kiesel, Jr., assistant mechanicalengineer of the Pennsylvania, represents an example of thismethod. Although this formula, in the form in which it ispresented does not take into account the spacing of the sidebearings, bolsters so designed have a greater relative sectionmodulus near their ends than would be the case were theydesigned to the first diagram of Fig. 1. This formula asgiven is based upon a fibre stress at the center of 12,500lb. per square inch. In order to demonstrate how a bendingmoment diagram constructed according to this method com-pares in a general way with the diagrams 1, 5, 6 and 7,the bending moment as called for by this equation is plottedas curve 8 in Fig. 2, the other diagrams being a series ofstraight lines. It is to be borne in mind, however, that value of the fibre stress used with diagrams , 6 and 7 range from 9,000 to 12,000 lb. per
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectrailroadengineering
