SHOP DRAWINGS FOR TRUSS BRIDGES. 401 



tlii^ \ it ss -how the elevation of the far girder as seen from tin- inside, with all field holes in flange* 

 and stilfencr.-. indicated and blackened. At one end of the elevation show in red the bridge-Beat 

 and hack wall, i;ive figures for distance from base of rail to top of masonry, notch of ties, depth 

 of girder, thickness of base-plate and of bed-plate or shoe. When the other end of girder has a 

 diiU rent height from base of rail to masonry, give both figures at the one end, and specify "for 

 this end" and "for other end." If span has bottom lateral bracing, a bottom view (horizontal 

 section) shall be shown below the elevation. When no bottom laterals are required, show only 

 end or ends of lower flange of girder, giving detail of base-plate and its connection to the flange. 

 1 )i tail the bed-plate separately, never show it in connection with the base-plate. 



Cross-frames shall, whenever possible, be detailed on the right hand of the sheet in line with 

 the elevation. The frame shall be made of such depth as to permit it being swung into place with- 

 out interfering with the heads of the flange rivets in the girders. Always use a plate, not a washer 

 with one rivet, at the intersection of diagonals. In skew spans it is always preferable to have an 

 uneven number of panels in the lateral system. 



Through Plate Girder Spans. Show on top of sheet an elevation of the far girder as seen from 

 inside; below this view show a horizontal section of span as seen from above with the lateral system 

 detailed complete. It is generally best to show floorbeams and stringers in red in this view and to 

 detail them on a separate sheet. The stiffeners in a through span should always be arranged so 

 that the floor system can be put in place from the center towards the ends. What is said under 

 " deck spans " about showing bridge-seat, back wall, detailing bed-plate separately, etc., applies 

 to through spans as well. 



TRUSS BRIDGES. General Rules. Before any details are started all c. to c. lengths of 

 chords, posts, diagonals, etc., shall be determined, and sketches made of shoes, panel-points, 

 splices, etc., so that the material can be ordered as soon as required. 



If not otherwise specified, camber shall be provided in the top chord by increasing the length 

 J in. for every 10 ft. for railroad bridges, and ^ in. for every 10 ft. for highway bridges. This 

 increase in length shall not be considered in figuring the length of the diagonals, except in special 

 cases, as directed by the engineer in charge. Half the increase in length shall be considered in 

 figuring the length of the top laterals. Particular attention must be paid to what is said under 

 "General Rules" about showing part of adjoining member in red, and about the small scale dia- 

 gram on every sheet. 



For every truss bridge an erection diagram shall be made on a separate sheet, giving the ship- 

 ping marks of the different members and all main dimensions, such as c. to c. trusses, height of truss, 

 number and length of panels, length of diagonals, distance from base of rail to masonry, distance 

 .from center of bottom chord or pin to masonry, size and grip of pins (Fig. 7), also show in larger 

 scale the packing at panel points, state any special feature which the erector needs to look out for, 

 and give approximate weight of heavy and important pieces when their weight exceeds five tons. 

 If in any place it is doubtful whether rivets can be driven in the field, the erection diagram and 

 also the detail drawings shall state that "turned bolts may be used if rivets cannot be driven." 

 A list giving number and contents of drawings belonging to the bridge shall also appear on the 

 erection diagram sheet. 



Riveted Truss Bridges. In square spans, not too large, show the left half of the far truss as 

 seen from the inside and detail all members in their true position, making scale of the skeleton one- 

 half the scale of the details. In skew spans, not symmetrical, show the whole of the far truss. In 

 large spans detail every member separately. When detailing web members bear in mind that the 

 intersection point on the chord must not be used as a working point for a member which stops 

 outside of the chord. A separate working point, preferably the end rivet, shall be established on 

 the member proper, and shall be tied up with the intersection point on the chord. 



The clearance between the chord and a web member entering same shall, whenever possible, 

 be not less than J in. in heavy and -fa in. in light structures. 



Members shall be marked with the panel points between which they go, for example, end- 

 post Ly-Ui', hip vertical Ui-Li; top chord U\-U t , etc., see Fig. 7. 



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