3 



10. Unless otherwise specified, the form of bridge trusses . 

 may be selected by the bidder ; for through bridges, the 

 end vertical suspenders and two panels of the lower chord, 

 at each end, shall be made rigid members. In general, all 

 spans shall have end floor beams for supporting the 

 stringers, ( 14.) ; and all floor beams shall be riveted to the 

 posts and vertical suspenders, above or below the pins, 



1 1 1), or to the chords. 



1 1. All lateral, sway and portal bracing must be made of Lateral Bracing, 

 shapes capable of resisting compression as well as tension, 



and must have riveted connections. ( 33, 40, 83). 



12. The wooden floors will consist of transverse ties or Wooden Floor, 

 floor timbers; their scantling will vary in accordance with 



the design of the supporting steel floor. ( 15.) They shall 

 be spaced with openings not exceeding six inches, and shall 

 be notched down inch and be secured to the supporting 

 girders by J-inch bolts at distances not over six feet apart. 

 For deck bridges the ties will extend the full width of the 

 bridge, and for through bridges at least every other tie 

 shall extend the full width of bridge for a footwalk. 



13. There shall be a guard timber (scantling not less than Guard Timbers. 

 6 x 8") on each side of each track, with its inner face parallel 



to and at feet inches from centre of track. Guard 



timbers must be notched one inch over every floor timber, 

 and be spliced over a floor timber with a half-and-half joint 

 of six inches lap. Each guard timber shall be fastened to 

 every third floor timber and at each splice with a three- 

 quarter (J) inch bolt. All heads or nuts on upper faces of 

 ties or guards must be countersunk below the surface of 

 the wood. ( 65). 



14. The guard and floor timbers must be continuous and 

 properly supported over all piers and abutments. 



15. The maximum strain allowed upon the extreme fibre Allowed strain 

 of the best yellow pine or white oak floor timbers will be n 



1,000 pounds per square inch. The weight of a single en- 

 gine wheel may be assumed as distributed over three ties, 

 spaced as per 



16. The floor timbers from centre to each end of span 



