SPECIFICATIONS FOK STEEL HIGHWAY BRIDGES. 39 
Through truss spans shall have sway bracing at each 
intermediate panel point if the height of the trusses is such 
as to permit a depth of 5 feet or more for the bracing. 
When the height of the trusses will not permit of such 
depth the top lateral struts shall be provided with knee 
braces. Top lateral struts shall be at least as deep as the 
top chord. Sway bracing shall be of ample strength to 
transfer one-half of the wind pressure to the leeward 
truss. 
Deck plate-girder spans shall be provided with cross ^^.^^^^ r o s s 
frames at each end proportioned to resist all lateral forces, 
and shall have intermediate cross frames at intervals not 
exceeding 1 5 feet. These frames shall be connected to the 
outstanding legs of the stiff ener angles and to the girder 
flanges. 
The vertical truss members and the floor beam connec- 62. Low truss 
tions of low truss spans shall be proportioned to resist a ^^^°^" 
lateral force, applied at the top chord panel points of the 
truss, determined by the following equation: 
i? = 150 (A^P) 
where 
i^ = lateral force in pounds. 
A = area of cross section of chord in square inches. 
P = panel length in feet. 
This rigidity may be secured in part by extending one 
or both 01 the floor beam connection angles upward along 
the inside of the post. Preferably outrigger brackets 
attached to the vertical posts on the outside of the trusses 
shall not be used. 
Through plate-girder spans shall be stiffened against .63. Through 
lateral deformations by means of gusset plates or knee^"^ er spans. 
braces with solid webs, attached to the stiff ener angles and 
floor beams. If the unsupported length of the inclined 
edge of the gusset plate exceeds 60 times its thickness, the 
gusset plate shall nave stiff ener angles riveted along its 
edge. 
These braces generally shall extend to the clearance 
line and preferably shall be spaced not farther apart than 
15 feet. 
Substantial railings shall be provided along each side 64. Raiimgs. 
of the bridge for the protection of traffic. In general the 
railings shall be of two classes, viz : 
1. Railings suitable for use on country bridges which are not 
subject to general pedestrian traffic. 
2. Railings for the protection of pedestrians on bridges in cities 
or villages. 
The top rail of all railiugs shall be located approximately 
3 feet 6 inches above the bridge floor and shall be capable 
of resisting a horizontal force of 100 pounds per linear 
foot. 
