224 STEEL RAILWAY BRIDGES. CHAP. IV. 



(5) Through truss spans shall have riveted portal braces rigidly connected to the end-posts 

 and top chords. They shall be as deep as clearance will allow, and shall be designed to carry to 

 the abutment the total wind force acting on the top chord. 



(6) At panel points of deck truss spans, having vertical members. Intermediate frames 

 shall be designed to carry \ the panel concentration of wind and centrifugal force to the bottom 

 chord and the end frame shall be designed to carry f the total wind and centrifugal force acting 

 on the top chord to the abutment. 



Frames for (i), (2) and (3) shall consist of single angle struts, top and bottom and double 

 diagonals. Frames for (4) may consist of knee braces attached to the top lateral struts, but pre- 

 ferably where clearance permits, of light open webbed girder. Portal frames shall consist of open 

 webbed girders, with knee braces connections to inclined posts. Frames for (6) shall consist of 

 double diagonals running between floorbeams and lower lateral struts and composed of two angles 

 back to back, or of two or four angles laced. 



2. Diaphragms for Twin Deck Spans. Diaphragms connecting two pairs of twin girders 

 are to be omitted on shallow spans. Where the girders exceed 3 ft. 6 in. in depth, diaphragms shall 

 be added for rigidity. They shall be connected to girders with field bolts. 



3. End Cross Frames and Diaphragms. In the design and location of end cross frames and 

 diaphragms their shape and position shall be such as to give access to the space between the 

 girders for inspection, painting and the placing of anchor bolts. 



REFERENCES. For the calculation of the stresses in railway bridges and for additional 

 details and the details of design, the following books may be consulted: Merriman & Jacoby's 

 "Roofs and Bridges," Part I, Stresses; Part II, Graphic Statics; Part III, Bridge Design; Part IV, 

 Higher Structures; Johnson, Bryan and Turneaure's "Framed Structures," Part I, Stresses, 

 Part II, Statically Indeterminate Structures and Secondary Stresses ; Part III, Design (in prep- 

 aration); Marburg's "Framed Structures," Part I, Stresses; Spofford's "Theory of Structures," 

 stresses in structures; DuBois's "Framed Structures"; Burr and Falk's "Design and Construction 

 of Metallic Bridges"; Skinner's "Details of Bridge Design," Parts I, II, III; Moore's "Design 

 of Plate Girders"; Ketchum's "The Design of Highway Bridges, "-stresses, details and design. 



