10 



Type of Truss 

 and Sections 

 of Members 



Spacing of 

 Stringers 



Floor Beams 



End Struts 



Design of 

 Bracing 



Sway Bracing 



75. If the depth of the web between the flange angles or side plates is less than 60 

 times the thickness of t he web, intermediate stiffeners may be omitted. 



76. Intermediate stiffeners shall be riveted in pairs to the web of the girder. The 

 outstanding leg of each angle shall not be less than 2 inches plus 1/30 of the depth of 

 the girder. 



77. Stiffener angles shall be placed at points of concentrated loading Such angles 

 shall not be crimped. 



77A. Trusses shall have single intersection web systems and preferably inclined 

 end posts. The top chords and end posts shall be made usually of two side segments 

 with one cover plate and with tie plates and latticing on the open side. The bottom 

 chords of riveted trusses shall be symmetrically made, usually of vertical side plates with 

 flange angles. Web members shall be made of symmetrical sections. 



77B. Ordinarily there will be two lines of stringers for each track and these will be 

 spaced 8 feet centre to centre. If four lines of stringers are used under one track, each 

 pair will be spaced symmetrically about each rail. 



78. Floor Beams shall preferably be set at right angles to the trusses or main girders 

 and they shall be rigidly connected thereto. 



79. End floor beams shall be provided where possible and they shall be designed for 

 jacking up the spans, under which condition the Unit Stresses herein specified shall not 

 be exceeded by more than 50 per cent. 



80. When impossible to use end floor beams with through spans, end struts and 

 stringer cross frames shall be provided, and these shall be rigidly connected to the string- 

 ers and to the trusses or main girders. Special provision shall be made for jacking up 

 the span from the masonry bridge seats. 



81. Lateral, longitudinal and sway bracing shall be composed of shapes with riveted 

 connections. When a double system of bracing is used, both systems may be considered 

 as simultaneously effective if the members meet the requirements both as to tension and 

 compression. 



82. The smallest angle to be used in bracing shall be 3> x 3 x % inch. Angles 

 shall be connected at their intersections by plates. 



83. Bottom lateral bracing shall be provided in all bridges, except deck plate girder 

 spans less than 30 feet long, from which it may be omitted. Top lateral bracing shall be 

 provided in all deck spans and all through truss spans. 



84. Continuous steel or concrete floors will be considered as the equivalent of lateral 

 bracing if the design and construction of such will fulfil the specified requirements. 



85. Lateral bracing beneath timber decks shall be low enough to clear the ties by 

 at least 1/2 inch. 



86. Through truss bridges shall be provided with portal bracing, rigidly connected 

 to the end posts and top chords; it shall be proportioned for total specified wind load on 

 the top chords, and shall be as deep as the specified clearance will allow. Furthermore, 

 sway bracing shall be provided at all intermediate principal verticals; or, in the case of 

 trusses having no intermediate vertical members, on all principal compression diagonals. 

 Sway bracing shall also be as deep as the specified clearance will allow- 



87. Deck truss spans shall be provided with brace frames at each end proportioned 

 to transfer the end reaction of the top lateral systems to the pier members. Deck truss 

 spans shall have intermediate brace frames at all intermediate principal verticals, or in 

 case there are no full depth intermediate verticals, on all principal compression diagonals. 



88. Deck plate girder spans shall be provided with brace frames at each end pro- 

 portioned to transfer the end reactions of the top lateral system to the pier members, and 

 shall have intermediate brace frames at intervals not exceeding 15 feet. 



