PLATE GIRDERS 39 



thickness of J in. and shall have their outstanding leg not over 

 3J in., unless they are supported by stiff eners at intervals not 

 over 30 in. Such shelf angles shall not be considered as a part of 

 the flange. 



Through plate girders shall preferably have their upper corners 

 neatly rounded off to a radius not exceeding 3 ft., or less than 

 one-third (J) of the depth of the girder. 



Where the bridge is composed of two or more spans only the 

 corners at the extreme ends need be rounded, unless the girders 

 vary in depth, in which case the deeper ones shall have their top 

 flanges rounded to meet the corner of the adjacent girder. (Par. 

 163.) 



158. Skew Bridges. Ends of deck-plate girders, and in 

 through bridges ends of track stringers at abutments, shall be 

 square to the track, unless a ballasted floor be used. 



159. Design of Girder. Plate girders shall be designed either 

 by the moment of inertia of their net section, or by assuming that 

 the flange areas are concentrated at their centers of gravity, in 

 which case one-eighth (J) of the gross section of the web, if 

 properly spliced, may be used as flange section. 



1 60. Design of Flanges. In girders having flange plates the 

 total flange area shall be so divided that forty per cent (40%) 

 or more will be concentrated in the flange angles and side plates, 

 if any, and the remainder in the cover plates. 



Where two or more cover plates are used they shall be of 

 equal thickness, or shall decrease in thickness outward from 

 the angles. 



161. Flange Plates. The flange plates of all girders shall be 

 limited in width, so as not to extend beyond the outer lines of 

 rivets connecting them to the angles more than 8 times the thick- 

 ness of the outside plate, or more than 5 in. (Par. 171.) 



All cover plates shall extend at each end at least 12 in. beyond 

 the points where they might be cut off theoretically. 



162. Flange Splices. Flange splices, where unavoidable, 

 shall be located at points where there is a considerable excess of 

 sectional area. Flange angles and flange plates shall all break 

 joints so that no two pieces will be spliced within 18 in. of each 

 other. In general no field splices will be allowed in girders less 

 than 70 feet long; this provision, however, does not apply to 

 work intended for export. (Par. 135.) 



