122 STEEL HIGHWAY BRIDGES. CHAP. III. 



PLATE GIRDERS. Plate girders are frequently used for highway bridges. Where the 

 conditions will permit deck plate girder bridges are to be preferred to through plate girder bridges 

 for highway service. The details of plate girders when used for highway bridges are essentially 

 the same as when used for railway bridges, which see. 



Details of a steel through plate girder highway bridge as designed by the Wisconsin High- 

 way Commission are shown in Fig. 15. Standard plans have been prepared for spans from 35 

 ft. to 80 ft., varying by 5-ft. intervals, and for i6-ft., i8-ft. and 2O-ft. roadway. Spans of 35 ft. 

 to 60 ft. inclusive have webs 60 in. by ^ in.; the 65-ft. and yo-ft. spans have webs 66 in. by ^ 

 in.; the 75-ft. spans have a web 66 in. to 72 in. by f in., while the 8o-ft. spans have a web 72 in. 

 to 78 in. by f in. For weights of plate girder bridges, see first part of this chapter. 



Details of a log-ft. span through-plate girder highway bridge built over the D. L. & W. R. R. 

 tracks in Jersey City, N. J., are given in Fig. 16. The girders were designed for a live load of 100 

 Ib. per sq. ft. on roadway and sidewalk; while the roadway floor was designed for a live load of 100 

 Ib. per sq. ft. and two 12,000 Ib. axle loads spaced 10 ft. apart with an allowance of 25 per cent for 

 impact. The expansion end is carried on 4-in. rollers. The concrete has a minimum thickness of 

 4 in. and is covered with i| in. of binder and 2 in. of asphalt. Each main girder weighed 1 12,000 

 Ib. ; and the total weight of steel in the bridge was about 403,000 Ib. 



LOW RIVETED TRUSS BRIDGES. Low riveted bridges are made with either Warren or 

 Pratt trusses, the Warren truss usually being preferred. The upper chords should be made of two 

 angles and a plate, two channels laced, or two channels with a top cover plate and lacing on the 

 bottom side of the member. The lower chord and the web members are made of two angles placed 

 in the same relative positions as in the upper chords. 



Details of a low riveted truss bridge with a reinforced concrete floor carried on steel stringers 

 or joists, as designed by the Iowa Highway Commission are shown in Fig. 17. The commission 

 has prepared standard plans for spans from 35 ft. to 85 ft. and with i6-ft. and i8-ft. roadway. 

 Spans over 65 ft. in length have one end supported on rockers. Spans 65 ft. or less in length have 

 one end supported on sliding plates. 



Details of a low riveted truss bridge with a reinforced concrete floor carried directly on the 

 floorbeams, as designed by the Iowa Highway Commission, are shown in Fig. 18. The commission 

 has prepared standard plans for spans from 35 ft. to IOO ft. and with i6-ft. and i8-ft. roadway. 

 Spans more than 65 ft. in length have one end supported on rockers. Spans 65 ft. or less in length 

 have one end supported on sliding plates. The reinforced concrete floor slabs have a thickness of 

 75 in. for an 8-ft. span, of 8 in. for a 9-ft. span, and of 8 in. for a lo-ft. span. The slabs are rein- 

 forced top and bottom with f in. square bars spaced 9 in. centers and i| in. from face of slab. 

 Transverse bars in. sq. are spaced about 2 ft. centers with one bar over the floorbeam. 



Details of a low riveted truss bridge with a reinforced concrete floor as designed by the Michi- 

 gan Highway Commission are given in Fig. 19. The Commission has prepared standard plans 

 for spans from 50 ft. to too ft. by 5-ft. intervals. 



The riveted low truss highway bridge with an inclined upper chord shown in Fig. 20 is built 

 by the American Bridge Company for locations requiring an artistic and serviceable bridge at a 

 moderate cost. This bridge has been built with six panels and with spans of 90, 96 and 102 ft. 

 The bridge in Fig. 20 has a 2O-ft. roadway and was designed for a dead load of 930 Ib. per lineal 

 foot of bridge, and a live load of 2,400 Ib. per lineal foot of bridge. The total weight of the steel 

 in this bridge, exclusive of joists and fence is, approximately, 57,000 Ib. The floorbeams are rolled 

 I-beams and are riveted below the chords. The top chords are made of two channels with a top 

 cover plate, the lower edges of the channels being fastened together with tie plates lacing is much 

 better practice. The bottom chord is composed of two angles, with tie plates tie plates are all 

 right for this member. The web members are made of 2 or 4 angles laced, as shown. Rods, not 

 shown, are used for the lower lateral system. 



Details of a low riveted truss bridge with a reinforced concrete floor as designed by the Wis- 

 consin Highway Commission are given in Fig. 21. Standard plans have been prepared for spans 

 from 35 ft. to 85 ft., and with i6-ft. and i8-ft. roadway. One end of all spans is carried on sliding 

 plates as shown. 



