The longest span of any suspension bridge, not only in America but in the world, is 1,600 feet. It is that of the Williamsburg Bridge over the East River at New York city and was completed in 1904. The span of the famous Brooklyn Bridge, completed in 1883, is 1,595% feet. The very handsome Manhattan Bridge, located between these two, has a span of 1,470 feet and was completed in 1909. A critical observation of these three bridges illustrates what can be done to improve the aesthetic fea tures of monumental bridges.
A bridge across the Charles River between Boston and Cambridge deserves especial men tion and marks a decided advance in the grow ing recognition on the part of municipal au thorities of the importance of esthetic consid erations in the design of public works. It consists of 11 spans of steel arches whose lengths range from 101% to 188% feet. Its width is 105 feet between railings. It is claimed that this bridge °will be not only one of the finest structures of its kind in this country, but will be a rival of any in the Old World.n Its length between abutments is 1,767% feet, and it was estimated to cost about $2,500,000.
The problems incident to the replacing and strengthening of old bridges frequently tax the resources of the engineer and demonstrate his ability to overcome difficulties. Only a few ex amples may be cited to indicate the character of this work. In 1900 the Niagara cantilever bridge had its capacity increased about 75 per cent by the insertion of a middle truss with out interfering with traffic. In 1897 the entire
floor of the Cincinnati and Covington suspen sion bridge was raised four feet while the traffic was using it. It may be of interest to state that the two new cables, 10% inches in diameter, which were added to increase the capacity of the bridge, have just about three times the strength of the two old ones, 12% inches in diameter, and which were made a little over 30 years before. In the same year the old tubular bridge across the Saint Lawrence River was replaced by simple truss spans without the use of false-works under the bridge and without interfering with traffic. On 25 May 1902, the Pennsylvania Railroad Bridge over the Raritan River and canal at New Brunswick, N. J., was moved sidewise a distance of 14% feet. Five simple spans 150 feet long and a drawbridge of the same length, weighing in all 2,057 tons, were moved to the new position and aligned in two minutes and 50 seconds. The actual times that the two tracks were out of service were respectively 15 and 28 minutes. On 17 Oct. 1897, on the same railroad near Girard Avenue, Philadelphia, an old span was moved away and a new one, 235 feet 7 inches long, put in exactly the same place in two minutes and 28 seconds. No train was delayed in either case.