210 STEEL RAILWAY BRIDGES. CHAP. IV. 



those given above; but the section shall not be less than required for live and dead loads and 

 centrifugal force. 



26. Net Section at Rivets. In proportioning tension members the diameter of the rivet holes 

 shall be taken |-in. larger than the nominal diameter of the rivet. 



27. Rivets. In proportioning rivets the nominal diameter of the rivet shall be used. 



28. Net Section at Pins. Pin-connected riveted tension members shall have a net section 

 through the pin-hole at least 25 per cent in excess of the net section of the body of the member, 

 and the net section back of the pin-hole, parallel with the axis of the member, shall be not less than 

 the net section of the body of the member. 



29. Plate Girders. Plate girders shall be proportioned either by the moment of inertia of 

 their net section; or by assuming that the flanges are concentrated at their centers of gravity; 

 in which case one-eighth of the gross section of the web, if properly spliced, may be used as flange 

 section. The thickness of web plates shall be not less than T ff of the unsupported distance 

 between flange angles (see 38). 



30. Compression Flange. The gross section of the compression flanges of plate girders shall 

 not be less than the gross section of the tension flanges; nor shall the stress per sq. in. in the 



compression flange of any beam or girder exceed 16,000 200 -r , when flange consists of angles 



only or if cover consists of flat plates, or 16,000 150^-, if cover consists of a channel section, 



where / = unsupported distance and b = width of flange. 



31. Flange Rivets. The flanges of plate girders shall be connected to the web with a sufficient 

 number of rivets to transfer the total shear at any point in a distance equal to the effective depth 

 of the girder at that point combined with any load that is applied directly on the flange. The 

 wheel loads, where the ties rest on the flanges, shall be assumed to be distributed over three 

 ties. 



32. Depth Ratios. Trusses shall preferably have a depth of not less than one-tenth of the 

 span. Plate girders and rolled beams, used as girders, shall preferably have a depth of not less 

 than one-twelfth of the span. If shallower trusses, girders or beams are used, the section shall 

 be increased so that the maximum deflection will not be greater than if the above limiting ratios 

 had not been exceeded. 



IV. DETAILS OF DESIGN. 



GENERAL REQUIREMENTS. 



33. Open Sections. Structures shall be so designed that all parts will be accessible for 

 inspection, cleaning and painting. 



34. Pockets. Pockets or depressions which would hold water shall have drain holes, or be 

 filled with waterproof material. 



35. Symmetrical Sections. Main members shall be so designed that the neutral axis will be 

 as nearly as practicable in the center of section, and the neutral axes of intersecting main members 

 of trusses shall meet at a common point. 



36. Counters. Rigid counters are preferred; and where subject to reversal of stress shall 

 preferably have riveted connections to the chords. Adjustable counters shall have open turn- 

 buckles. 



37. Strength of Connections. The strength of connections shall be sufficient to develop the 

 full strength of the member, even though the computed stress is less, the kind of stress to which 

 the member is subjected being considered. 



38. Minimum Thickness. The minimum thickness of metal shall be f-in., except for 

 fillers. 



39. Pitch of Rivets. The minimum distance between centers of rivet holes shall be three 

 diameters of the rivet; but the distance shall preferably be not less than 3 in. for f-in. rivets and 

 25 in. for f-in. rivets. The maximum pitch in the line of stress for members composed of plates 

 and shapes shall be 6 in. for f-in. rivets and 5 in. for f-in. rivets. For angles with two gage lines 

 and rivets staggered the maximum shall be twice the above in each line. Where two or more 

 plates are used in contact, rivets not more than 12 in. apart in either direction shall be used to 

 hold the plates well together. In tension members, composed of two angles in contact, a pitch 

 of 12 in. will be allowed for riveting the angles together. 



40. Edge Distance. The minimum distance from the center of any rivet hole to a sheared 

 edge shall be i| in. for f-in. rivets and I J in. for f-in. rivets, and to a rolled edge I \ in. and l| in., 

 respectively. The maximum distance from any edge shall be eight times the thickness of the 

 plate, but shall not exceed 6 in. 



