19 



106. All through bridges shall have latticed portals, of 

 approved design, at each end of the span, connected rigidly Bracing. 

 to the end posts and top chords. They shall be as deep as 



the specified head-room will allow, and provision shall be 

 made in the end posts for the bending strains from lateral 

 forces. (4, 11,24.) 



107. When the height of the trusses exceeds 25 feet, an 

 approved system of overhead diagonal bracings shall be 

 attached to each post and to the top lateral struts. 



108. Pony riveted trusses and girders shall be stayed by 

 knee braces or gusset plates at the ends and at intermediate 

 points. 



109. All deck girders shall have transverse braces at the 

 ends. All deck bridges shall have transverse bracing at 

 each panel point, of sufficient strength to carry half the 

 maximum strain increment due to lateral and centrifugal 

 forces. This bracing shall be proportioned in double-track 

 bridges to resist the unequal loading of the trusses, with 

 one track loaded. 



no. In double-track deck bridges, where three trusses 

 are used, all three trusses will be made of equal strength ; 

 the unequal loading being distributed through the trans- 

 verse diagonal bracing as a live load. (For the purpose 

 of reducing the unequal deflection under single-track load- 

 ings.) 



in. At all points where floor beams, portals or other Diaphragm*, 

 bracing connect with the posts or chords, proper diaphragms 

 must be inserted to distribute the loads and forces over 

 the full section of these posts or chords. 



112. All members of the web, lateral, longitudinal or sway 

 systems must be securely riveted at their intersections to 

 prevent sagging and ratlin 



113. All bed-plates must be of such dimensions that the Bed-pu. 

 greatest pressure upon the pedestal stone shall not exceed 



250 pounds per square inch. Their upper bearing surfaces 

 should, preferably, be at least six inches above the masonry. 



114. All bridges over 80 feet span shall have hinged Friction Rollers, 

 bolsters at both ends, and at one end nests of turned fric- 



