Scientific American—December 31, 1892


There are three railroad bridges across the Harlem River, the estuary connecting the water of Long Island Sound with the Hudson River. The principal one of these bridges, situated in the line of Fourth Avenue, is used by the New York Central, the Harlem, and the New Haven Railroads for their passenger traffic principally. An immense number of trains pass over it daily, so much so that it has become insufficient for its uses. It included always a center swinging draw. This draw was struck so often by passing boats that apprehensions were entertained as to its working perfectly. Accordingly, to preserve the integrity of the river navigation, and also of the railroad transit, an auxiliary draw was erected adjoining the swinging draw. This second one, from the designs of Mr. G H. Thompson, of the New York Central road, was of the lifting type. In the upper cut, this draw is seen in position nearest the front of the picture, while immediately back of it is the old swinging draw. The floor of the new drawbridge was carried on the top of plate girders, which were free to swing up or down on horizontal pivot or hinge joints immediately adjoining the front of the tower. To open the draw, it was simply pulled upward, rising into a vertical position. To effect this operation, cable hoisting machinery was provided, and to give scope to its operation, the tower, shown in the cut, was erected.

The tower is an iron lattice work structure, 126 feet high, with a base 34 feet 6 inches wide and 48 feet 6 inches long. Its front pillars are vertical, and within them counter weights were provided to relieve the hoisting machinery of most of the strain of lifting the draw. It will be seen that in raising the bridge from a horizontal position, less and less power is required. Accordingly, the system was so arranged that as the bridge rose, counterweights were successively detached, thus compensating for the decreased moment of the structure. The bridge has now to be removed and replaced by another structure. Independent of the requirements of present traffic on the Harlem River, it is obvious that when the improvements now under way shall have been completed by the Federal government, it will become a waterway of considerable importance to the city. The bridge also is of increasing importance with regard to the railroad traffic, and the opening of its draw, even now, has had to be restricted, owing to the number of trains which have to pass it. A new bridge is to be built, elevated nearly 30 feet above the water, so that the majority of boats can go under it without the draw being opened. In accordance with the requirements of the Federal government, the new draw in the new bridge will have to give a minimum opening of 100 feet at right angles to the axis of the stream. As the bridge runs at an angle with this axis, the full opening of the draw will exceed 165 feet on each side of the center pier. The drawbridge truss which will swing in its center therefore will be about 400 feet long, and will carry four lines of tracks. The bridge will be the continuation of the elevation of the tracks in Fourth Avenue—a colossal work soon to be begun.

To enable the new bridge to be constructed, a temporary bridge is to be built at one side of it, which is shown in the upper cut. When this bridge is finished, trains will use it, and the old structure will be demolished and replaced by the elevated bridge just mentioned. The temporary bridge, however, must have a draw, and the Federal engineers exacted a minimum width, requiring trusses 106 feet long. The old trusses of the lifting draw spanned but a little more than 90 feet. To provide the new draw for the temporary bridge, it was determined first to move the tower bodily into position in line with the temporary bridge, and to use it to raise and lower the lattice girder draw, 106 feet in span. The line of travel of the tower having been decided on, rows of piles were driven; caps were placed on them, and on these 12 by 12 longitudinal timbers were placed. Rails were then spiked down on the timbers so as to form a horizontal sliding way. The tower was jacked up bodily 3 feet after being stripped of counter weights and other material so as to make it as light as possible. It is calculated that 100 tons weight were thus removed, of which 85 tons were represented by the counter weights alone. Even when this was done, the residual weight was in the neighborhood of 180 tons. When the tower was thus elevated, slideways in continuation of those laid on the outside were placed under it. The rails were lubricated with Dixon's plumbago lubricator and the tower was lowered upon them. A six-spool hoisting engine with falls of very large size, with great sheave blocks, being 18 inches in diameter, was arranged to draw the tower away from the bridge along the line of the slide. Some apprehension was felt as to the success of the operation, but it was found that the tower might be moved a distance of 8 feet without interfering with traffic, so it was decided that here, at least, was room for experiment. Accordingly, before the final operation, the tower was moved back and forth to distances of a few feet to test the practicability of the operation. When everything was ready, the final operation of moving, illustrated in the lower cut, was executed. It was done at night, in order to avoid interruption to traffic. At 12:30 A. M., the tracks were cut by the railroad company, and the way was cleared for the tower to be drawn out from its position. The foreman in charge of the work, as a signal code, arranged at one motion of his hand to indicate one revolution of the engine. When all was clear, the engine was started, first slowly, and then more rapidly, and in 21 minutes the great mass was moved 54 feet. The railroad company replaced the tracks, and by 3:20 A. M. all was ready for traffic once more. There was absolutely no interruption to traffic. The tower is to be moved along on its present course until the line of the new temporary bridge is reached, when it is to be moved forward in position. When installed here, the lattice girders will be put in position. As this will then be the only drawbridge, hoisting machinery of double the power of the original will be put in, so as to insure rapid operation.

The work of moving the tower was done by the firm of Coffrode & Saylor, of this city, who were its original constructors. All the operations were in charge of their foreman, Mr. Maylan, and the entire work was successful in every sense of the word.

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