222 STEEL RAILWAY BRIDGES. CHAP. IV. 



Rivets in Stiff eners. Rivets in stiffener angles may have the maximum spacing, except that: 



(a) Rivets in end stiffeners and stiffeners at concentrated loads shall develop the full computed 

 stress in the stiffeners. 



(b) Spacing of rivets in end stiffeners, intermediate stiffeners, and web splices shall be identi- 

 cal, except that rivets in any line may be omitted where possible without exceeding the maximum 

 specified pitch, in order to minimize shop work of punching. 



Holes for Hand-Hooks. All stiffeners on deck girders with concrete decks and ballast floors 

 should have holes punched in the outstanding legs for inserting hand-hook to support a person 

 inspecting bridge. Holes should be jf in. diameter and located 6 in. from top flange on shallow 

 girders and 6 ft. from bottom flange on deep girders. Gage line of hole to be l| in. from outer 

 edge of angle. 



STRINGERS AND FLOORBEAMS. I. Stringers. Stringers for through girder spans 

 may be either I-beams or built girders. Where I-beams are used two stringers shall be placed 

 under each rail. Depth of stringers shall depend on available distance from base of rail to "low 

 bridge"; depth shall be preferably to i, but not less than T V, the panel length. 



2. Floorbeams. Depth of floorbeams shall be such as to allow stringers to be framed readily 

 into the web, and not less than | of the distance center to center of girders or trusses. 



3. Stringer Connections. Stringers shall be riveted to webs of floorbeams with f in. con- 

 nection angles. Connection angles are to be faced to provide uniform bearing against webs of 

 floorbeams. Make stringers yj in. short at each end for clearance in erecting. 



4. Floorbeams for Through Girders. The gusset plates connecting floorbeams to main 

 girders shall, wherever possible, extend to the top of the girder and shall have an angle riveted 

 along the edge, to form an effective stay for the top flange of the main girder, and they shall also 

 form the webs of the end portions of the floorbeams, extending out toward the center as far as the 

 clearance line will allow, and being there spliced to the main web. 



5. Floorbeams for Truss Bridges. Floorbeams for truss spans shall preferably be riveted to 

 the vertical posts or hangers, extending the connection angle above the top flange where necessary 

 to secure sufficient rivets. When it is necessary to cut away the lower corner of the floorbeam to 

 clear the chord, special care shall be taken to so reinforce the web as to carry the end shear into 

 the connection angles. 



TRUSS AND TOWER MEMBERS. i. Top Chord and End-post. The top chord and 

 the inclined end-post shall usually consist of two built channels, with a thin cover plate on top 

 and with bottom flanges latticed. The bottom flanges shall be made heavier than the top, in 

 order that the gravity axis may come as close as possible to the center line of the webs. 



2. Verticals and Rigid Tension Members. Intermediate posts shall usually consist of two 

 rolled or built channels latticed. Hip verticals and similar members and the two end panels 

 of the bottom chords of single track pin-connected trusses shall be rigid, and may consist either 

 of two rolled or built channels latticed; or of four angles latticed to form an I-section. 



3. Eye-bars. Eye-bars shall be used for all bottom chord members and main diagonals that 

 do not require to be stiffened in pin-connected trusses. Dimensions of heads shall be according 

 to manufacturers shop standard. Length of eye-bars shall be given on the drawings, center to 

 center of pin holes, and also back to back of pin holes. 



4. Eccentricity. The line of applied force must coincide with the gravity axes of built 

 members or else the member must be designed for combined direct stress and flexure due to the 

 eccentricity of the applied load. 



5. Bending Due to Weight. Bending moment in the top chord and end-post due to weight 



p 



of member may be computed by the approximate formula, -r db M-c/I, where P = total direct 



A 



stress in the member; A = gross area of the section of the member; M = bending moment at the 

 section of the member in in.-lb.; c = distance to extreme fiber; and / = moment of inertia of the 

 section of the member, and the stress from such bending shall be deducted from the average 

 compressive stress allowed by the column formula. 



6. Bending in End-posts. In computing stresses in the end-post of through pin-connected 

 trusses, due to wind force, where the end-post consists of two built or rolled channels, if the product 

 of the wind reaction in the top chord times one-half the distance from the foot of the post to the 

 lowest connection of the portal bracing does not exceed the product of the dead load stress in one 

 of the channels composing the end-post times the distance center to center of the bearings of the 

 channels on the pin, the post may be considered fixed-ended and the point of contra-flexure 

 assumed midway between the foot of the post and the lower connection of the portal bracing. 

 Otherwise it must be considered pin-connected. The end-posts of riveted through trusses shall 

 be considered as fixed-ended columns. 



7. Over-run of Angles. Where side plates are used on chord sections placed between the 

 flange angles, at least | in. clearance should be allowed between the edges of the plate and the 

 angles to allow for over-run of angles. 



