118 



STEEL HIGHWAY BRIDGES. 



CHAP. III. 



The maximum span for beam bridges should be 30 ft. Riveted truss bridges or plate girders 

 should be used for spans of 30 ft. and upwards for country bridges, and plate girders for heavy city 

 bridges. Riveted bridges for spans of, say 40 ft., are more economical than plate girder bridges 

 and will give fully as great a length of service if properly designed and constructed. The ends of 

 beam bridges should always be supported on masonry abutments. 



TABLE IX. 

 ESTIMATED QUANTITIES FOR STANDARD BEAM SPANS. IOWA HIGHWAY COMMISSION. 



TABLE X. 



STEEL I-BEAM BRIDGES. WISCONSIN HIGHWAY COMMISSION. 

 Channels on outside. Weight includes railing. 



