TYPES OF BRIDGES. Ill 



Massachusetts Public Service Commission. The types of highway bridge recommended by 

 the commission are as follows: 



Sttel Bridges. For spans up to 20 ft., wooden stringers or rolled beams; for spans from 20 ft. 

 to 40 ft., rolled beams or plate girders; for spans from 40 ft. to 70 ft., plate girders; for spans from 

 70 it. to 100 ft., plate girders or riveted trusses; for spans from loo ft. to 125 ft., riveted trusses; for 

 span* from 125 ft. up, riveted or pin trusses. 



Wisconsin Highway Commission. The types of highway bridge recommended by the com- 

 mission are as follows: 



Concrete Bridges. Spans of i| ft. to 10 ft., slab culverts and bridges; spans 10 ft. to 18 ft., 

 slab bridges; spans 10 ft. to 40 ft., through girders. 



Steel Bridges. Spans 10 ft. to 38 ft., rolled beams; spans 35 ft. to 80 ft., Warren riveted low 

 trusses or plate girders; spans 80 ft. to 135 ft., Pratt riveted high trusses; spans over 135 ft., riveted 

 high trusses with curved chords. 



WIDTH OF ROADWAY. The following data will show standard practice. 

 Illinois Highway Commission. The widths of roadways are specified for State Aid Routes, 

 'rincipally Traveled Roads, and Secondary Roads. 



On Designated State Aid Routes. Bridges up to and including 10 ft. span, 20 to 30 ft. roadway; 

 ridges over 10 ft. up to and including 60 ft. span, 1 8 to 24 ft. roadway; bridges over 60 ft. span, 

 16 to 20 ft. roadway. 



On Principally Traveled Roads. Bridges and culverts 10 ft. or less in span, 20 to 30 ft. road- 

 iray; bridges over 10 ft. and up to and including 60 ft. span, 16 to 20 ft. roadway; bridges over 60 

 t. span, 1 6 to 1 8 ft. roadway. 



On Secondary Roads. Bridges and culverts 10 ft. or less in span, 18 to 24 ft. roadway; bridges 

 jr 10 ft. span, 16 ft. roadway. 



Culverts Under Fills. The length of the barrel of the culvert shall have a length that will 

 jrmit of side slopes of ij horizontal to i vertical, and a top width of 20 to 30 ft. on State Aid 

 Dutes, 20 to 30 ft. on Principally Traveled Roads, and 1 8 to 24 ft. on Secondary Roads. 



Iowa Highway Commission. The widths of roadway for highway bridges as recommenedd 

 jy the commission are as follows: 



Concrete Bridges. For box or arch culverts with spans of 2 ft. to 16 ft., 24 ft. roadway for 

 junty roads, and 20 ft. for township roads; for slab bridges with spans over 16 ft. span, 20 ft. 

 idway for county roads, and 18 ft. for township roads; for girder bridges over 16 ft. span, 20 ft. 

 idway ; for arches over 16 ft. span, 24 ft. roadway for county roads, and 20 ft. for township roads, 

 "he slopes on fills shall be I \ horizontal to i vertical. 



Steel Bridges. A roadway of 20 ft. on county roads, for all spans, and 18 ft. on township roads 

 )r all spans. The minimum legal width of rpadway is 16 ft. 



Association of State Highway Departments. The following minimum widths of concrete 

 ridges are recommended. 



For First Class Roads. Culverts under 12 ft. span, 24 ft. roadway; slab bridges over 12 ft. 

 in, 20 ft. roadway; all other spans 20 ft. roadway. 



For Second Class Roads. Culverts under 12 ft. span, 20 ft. roadway; slab bridges over 12 ft. 

 in, 18 ft. roadway; all other spans, 18 ft. roadway. 



For Third Class Roads. Culverts under 12 ft. span, 20 ft. roadway; slab bridges over 12 ft. 

 in, 1 8 ft. roadway; longer bridges, 16 ft. roadway. 



The above widths of concrete bridges have been adopted by the Wisconsin Highway Com- 

 sion. 



LOADS. The loads carried by a bridge consist of (i) fixed or dead loads, (2) the moving or 

 live load, and (3) miscellaneous loads. 



The dead load consists of the weight of the structure and is always carried by the bridge; the 

 live load consists of the moving load which the bridge is built to carry, while the miscellaneous 

 loads include wind loads, snow loads, etc. Data on dead loads are given in the " Specifications for 

 Steel Highway Bridges " in the last part of this chapter. 



WEIGHTS OF BRIDGES. The weight of a bridge is composed of (i) the weight of the steel 

 in the steel framework, consisting of the vertical trusses, the upper and lower lateral systems, the 

 floorbeams, the portals and sway bracing; (2) the weight of the joists and the fence; and (3) the 

 weight of the floor covering. 



