July 4, 1902 ] 



SCIENCE. 



17 



the large ratio of the moving load to the 

 dead load, or weight of the bridge itself. 



While riveted bridges are now quite gen- 

 erally nsed for spans from 100 to 150 feet, 

 they have been employed to some extent 

 up to 181^ feet. The recent forms of 

 riveted trusses do not, however, conform 

 to the general character of European de- 

 signs but embody the distinctively Ameri- 

 can feature of concentrating the material 

 into fewer members of substantial con- 

 struction. With but rare exceptions the 

 trusses are of the Warren, Pratt and Balti- 

 more types with single systems of webbing. 

 At a distance where the riveted connec- 

 tions cannot be distinguished, the larger 

 trusses have the same general appearance 

 as the corresponding pin bridges. 



The recent examples of viaduct construc- 

 tion with their stiff bracing of built-up 

 members and riveted connections exhibit 

 a marked contrast to the older and lighter 

 structures with their adjustable bracing 

 composed of slender rods. The viaduct 

 which carries the Chicago and Northwest- 

 ern Railroad across the valley of the Des 

 Moines River, at a height of 185 feet above 

 the surface of the river is 2,658 feet long. 

 It was built in 1901, is the longest double- 

 track viaduct in the world, provided those 

 located in cities be excluded, and is an 

 admirable type of the best modern con- 

 struction. The tower spans are 45 feet long 

 and the other spans are 75 feet long. Four 

 lines of plate girders support the two tracks. 

 Along with this viaduct should be mention- 

 ed the Viaduct Terminal of the Chesapeake 

 and Ohio Railway at Richmond, Va., whose 

 length including the depot branch is 3.13 

 miles. A large part of this is not very 

 much higher than an elevated railroad in 

 cities. The excellent details and elean 

 lines of this substantial structure give it 

 a character which is surpassed neither in 

 this cousitry nor abroad. It may be added 

 that the highest viaduct in this country, 



and which was rebuilt in 1900, is located 

 seventeen miles from Bradford, Pa., where 

 the Erie Railroad crosses the Kinzua Creek 

 at a height of 301 feet. It has a length of 

 2,053 feet. 



While the elevated railroads which have 

 been built recently, also embody many of 

 the characteristics of the best viaduct con- 

 struction, special study has been given to 

 improve their esthetic effect. The use 

 of curved brackets, of connecting plates 

 whose edges are trimmed into curves so 

 as to reduce the number of sharp angles, 

 and of rounded corners of posts, constitute 

 some of the means employed. The results 

 are seen in the structures of the Boston 

 Elevated Railroad and in some of the latest 

 construction in Chicago. 



The longest span of any simple truss 

 in America is that of the bridge over 

 the Ohio River at Louisville, erected in 

 1893. Its span center to center of end 

 pins is 546^ feet. Since that time sev- 

 eral other bridges of this kind have 

 been built which are considerably heavier, 

 although their spans are somewhat shorter. 

 The most noteworthy of these are the 

 Delaware River bridge on the Pennsylvania 

 Railroad near Philadelphia and the Mo- 

 nongahela River bridge of the Union Rail- 

 road at Rankin, Pa., both of which are 

 double-track bridges. The Delaware 

 River bridge was erected in 1896, each one 

 of its fixed spans having a length of 533 

 feet and containing 2,094 tons of steel. 

 The Rankin bridge was erected in 1900. 

 Its longer span has a length of 495 feet 

 8-J inches between centers of end pins and 

 contains about 2,800 tons of steel, making 

 it the heaviest single span ever erected. It 

 may also be added that the locomotive and 

 train load for which this bridge was de- 

 signed is the heaviest that has yet been 

 specified. 



The recent changes in the details of pin- 

 connected truss bridges have been mainly 



