128 



STEEL HIGHWAY BRIDGES. 



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CHAP. III. 



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FIG. 23. DETAIL PLANS OF THROUGH HIGH TRUSS SPAN. 



COMMISSION. 



WISCONSIN HIGHWAY 



HIGH TRUSS STEEL HIGHWAY BRIDGES. Through truss bridges with spans of from 

 80 to 170 ft., are built with parallel chords and preferably with riveted joints. For spans of from 

 1 60 to 220 ft. bridges are usually built of the Pratt type with inclined upper chord (camel-back) 

 trusses. Above 220 ft., bridges are usually built with the Petit type of truss. The above limits 

 are approximate only. For long span bridges the inclined chord truss with K-bracing is rapidly 

 taking the place of the Petit truss. High truss pin-connected bridges should never be built with 

 less than five panels. 



Types of bridge adopted in the American Bridge Company's standards are as follows: 



Pratt, pin-connected trusses 80 to 168 ft. span 



Pratt, riveted trusses. .- 80 to 168 ft. span* 



Warren, quadrangular, riveted trusses 80 to 152 ft. span' 



Inclined chord Pratt (camel-back), pin-connected trusses 168 to 220 ft. span- 

 Petit trusses, pin-connected 220 ft. span and over 



Examples of High Truss Highway Bridges. Details of a high truss steel highway bridge as 

 designed by the Wisconsin Highway Commission are shown in Fig. 22 and Fig. 23. Standard plans 

 have been prepared for spans of 90 ft. to 150 ft., varying by 5-ft. intervals, and a roadway of 16 ft. 

 and 1 8 ft. All spans have one end carried on rockers as shown. These designs have been worked 

 out very economically by Mr. M. W. Torkelson, bridge engineer, and represent the extreme econ- 

 omy of design that will conform to good practice. 



Details of a high truss steel highway bridge as designed by the Iowa Highway Commission are 

 given in Fig. 24. Standard plans have been prepared for spans of 90 ft. to 150 ft. varying by 

 5-ft. intervals, and a roadway of 16 ft. and 18 ft. All spans have one end carried on rockers as 

 shown. The designs are well worked out with the exception of the collision strut in the first panel, 

 which should be omitted. 



