424 STRUCTURAL DRAFTING. CHAP. XII. 



Live Load. (Diagram of wheel loads.) 



Wind Load. 



Diagrams. In general, the design shall show an elevation of the truss, plan of top lateral 

 bracing, plan of bottom lateral bracing and stringer bracing, half end view showing portal, half 

 intermediate view, or as many intermediate views as are necessary to show intermediate sway 

 frames. The end view shall show track in place with information similar to that for plate girders. 

 The design of a pin-connected bridge shall show the sizes of pins and the arrangement of the 

 members at all panel points. 



Stresses. Give the stresses in all members of trusses as follows: D. L. (Dead Load); L. L. 

 (Live Load); I. (Impact); C. (Curvature); W. (Wind Stresses). Also total stresses. 



Always use the minus sign for tensile stress and the plus sign for compressive stress. Compute 

 and give traction stresses for viaduct towers. 



For stringers and floorbeams give the bending moment and shear and stresses in the same 

 manner as for plate girders. 



General Dimensions. The most important dimensions are, number of panels and length, 

 depth of truss at every panel point if upper chord is curved, distance c. to c. of trusses, distance 

 base of rail to masonry, distance center of end pin to masonry, distance c. to c. of end pins and 

 face to face of masonry, or c. to c. of piers. If the bridge be on a curve, give the degree and show 

 direction of curvature, the distance of base of low rail to masonry, and the super-elevation of 

 outer rail. Note that greater clearances are required on curves. Show the clearance line and line 

 of base of rail in the elevation of truss. 



Compression Members. Give the actual unit stress, the allowable unit stress, radius of 

 gyration, moment of inertia, actual and required area, eccentricity and cross-section. 



Tension Members. Give allowable and actual stresses, the required and actual net area. 

 For built sections give number of holes deducted for rivets in obtaining net area, and radius of 

 gyration. 



Sections. Give section of every member and thickness of all gusset plates. Always give 

 size of lacing bars, and state whether single or double lacing is required. 



Built Sections. On all built sections give depth of section, and in using plate and angle 

 sections, make the web | in. less in width than the depth of section. 



Angles with Unequal Legs. In any member composed of one or more angles with unequal 

 legs, show clearly the direction in which the long or short leg is turned. 



Rivets. Note the number of rivets to be used for end connections of all members, and give 

 the number of rivets in single shear required at end connection of track stringers. 



Shoes or Pedestals. Give maximum reaction, required and actual area of masonry plate, 

 with allowable pressure on masonry. Note size of bed plate, and show in position with location 

 of holes for anchor bolts. Note size and number of rollers for expansion pedestal, and also whether 

 pedestal is built, cast iron or steel. 



Camber. The amount of camber should be shown on the design. 



Notes. Same as for Plate Girders. 



