164 



STEEL RAILWAY BRIDGES. 



CHAP. IV. 



TABLE III. Continued. 

 MAXIMUM MOMENTS, M; END SHEARS, S; AND FLOORBEAM REACTIONS, R; PER RAIL, FOR 



GIRDERS. 

 Cooper's E6o Loading (A. R. E. A.)- 



CALCULATION OF STRESSES. For the calculation of stresses in railway bridges, see 

 the author's "The Design of Highway Bridges;" Johnson, Bryan & Turneaure's "Framed Struc- 

 tures," Part I; Marburg's "Framed Structures," Part I; Spofford's "Theory of Structures"; or 

 other standard textbook. 



Moments, End Shears and Floorbeam Reactions. The maximum bending moments and 

 end shears, for Cooper's E 60, and A. R. E. A. special loadings, for girders up to 125 ft. span are 

 given in Table III. The maximum moments occur at a point near the center of the girder. 

 Maximum floorbeam reactions are given for stringers up to 40 ft. span. The table also gives 

 the impact stress calculated for A. R. E. A. impact formula (4). 



The maximum moments, end shears, quarter-point shears, center shears, and maximum 

 floorbeam reactions for girders up to 75 ft. span are given in Table IV. 



Moment Diagram. A diagram giving the position of the wheels in Cooper's E loadings that 

 will produce maximum moment in a beam or at a panel point in a truss is given in Table Va. 

 The condition for maximum shear in the first panel is the same as for bending moment at Li, 

 which value may be obtained from Table Va. Other loadings for maximum shear must be cal- 

 culated by means of the criterion given above. 



A moment diagram for Cooper's E 60 loading is given in Table Vb, and brief instructions 

 for use of the table are given on the page opposite Table Vb. 



Shears in Bridges. Shears in the panels of the loaded chords of spans with 3 to 9 panels, 

 for Cooper's E 50 loading, are given in Table VI, Table VII, and Table VIII. To obtain the 

 shears for E 60 loading multiply the tabular values by f . The stresses in the web members of a 

 Pratt truss are equal to the shears X sec 0, where 6 is the angle that each web member makes with 

 a vertical line. The tables were calculated by the McClintic-Marshall Construction Company. 



Moments in Bridges. Bending Moments in beams and girders and at points in the loaded 

 chord of bridges, are given in Table IX and Table X. The bending moments for an E 60 loading 

 will be equal to the tabular values X f . 



For example, the bending moment for an E 50 loading, at joint L\, in an 8 panel truss of 2OO-ft. 

 span from Table X, is 6,787 thousand ft.-lb. For an E 60 loading the bending moment at joint 

 Li is 6,787 X 6/5 = 8,145 thousand ft.-lb., which checks the value calculated from Table Vb 

 on the page opposite Table Vb. The tables were calculated by the McClintic-Marshall Con- 

 struction Company. 



Elevated Trestle Span Reactions. The floorbeam reactions and the maximum reactions of 

 the intermediate and tower spans of elevated railway trestles may be calculated from Table IX 

 and Table X, as follows: 



Required the end reactions for a 40 ft. tower span and an 80 ft. intermediate span. Take a 

 span equal to 40 + 80 = 120 ft., and calculate the bending moment at a point 40 ft. from the 

 left end. In Table IX, take a 6-panel bridge with 20 ft. panels, the bending moment at L 2 is 



