BETWEEN NEW YORK AND BROOKLYN.
SCIENTIFIC AMERICAN SUPPLEMENT
NOVEMBER 25,1876. No.48.
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BETWEEN NEW YORK AND BROOKLYN. SCIENTIFIC AMERICAN SUPPLEMENT NOVEMBER 25,1876. No.48.
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THE EAST RIVER SUSPENSION BRIDGE CABLE MAKING. THE East River bridge may be said, at the present moment, to be in a state of reparation for the commencement of operations on the first part of the third stage of its erection, the first being the sinking of the subfluvial foundations and those of the anchorages; the second, the building of the piers and anchorages; and the third, the construction of the super-structure. It will be remembered by our readers that this bridge, which spans the East River from New York to Brooklyn, has a central span from pier to pier of 1595 feet 6 inches, and half spans of 930 feet each from the piers to the anchorages. The towers are 270 feet in height above the water-line, and the centre of the roadway when suspended will be 135 feet above mean tide-water, allowing clear passage to all vessels of less than 1000 tons, those of greater tonnage being obliged to lower their top-gallant masts. When finished, the bridge and approaches will have the immense total length of 5989 feet, or nearly one and one eighth miles. The towers rest on timber foundations about 78 feet below high water, and at the water-line are 141 feet broad and 59 feet thick. By referring to the SUPPLEMENT, Vol. 1, No.19, the reader will find detailed drawings, an elevation and section of the Brooklyn tower, together with a full description of both towers of the bridge; and in Vol. 34, No.2, of the SCIENTIFIC AMERICAN, is given a careful description of the building of the New York anchorage, together with a perspective drawing of the anchorage, a section showing the disposition of the anchor plates and chains, and a drawing of an anchor plate. The Brooklyn tower was commenced in the summer of 1870 and the New York tower in 1872. Both are now finished as far as possible before the making and placing in position of the cables. 
The making of the cables, from which the roadway is to be suspended, belongs to the third stage of the erection of the bridge, though it possesses snch a distinctive interest that it merits being considered as a separate and intermediate stage between the building of the masonry and the suspension of the roadway. The main cables, of which there are to be four, will each be sixteen inches in diameter, having a tensile strength of 100,000 Ibs. per square inch of cross section, and composed of 6289 wires of chrome steel 165/1000, or, say, 3/16" in. in diameter, No.6 gauge, divided into nineteen strands of 331 wires each. These strands are to be constructed separately, and when finished to be made into the main cable. The cables are to be constructed in mid air, not far from the position they will occupy when ready for the wire-rope suspenders which support the roadway. The apparatus used in the construction of the cables necessitates the use of five distinct sets of galvanized chrome steel wire ropes. According to the specifications, they are to be as follows: First, four working ropes (for pulling over the cable wires), afterwards spliced into two continuous ones, and passing at each anchorage around sets of tension wheels. These ropes are t in. in diameter; have a length of 3800 feet each, and a breaking strength of not less than 18 tons; weigh 7/8 Ib. per foot, making a total weight for all four ropes of 13,300 Ibs.; are composed of six strands seven No.14 wires each, laid around a central core or tarred hemp, and have a lay of about one turn in 6-1/4 inches. Second, two" carrier" ropes (temporary ropes used for carrying over the heavier or the ropes required for the cable-making apparatus), being respectively 1-3/4 and 1-1/8 in. in diameter, having lengths of 3716 feet each, breaking strengths or not less than 108 and 50 tons, weighing 3 lbs. per foot, and having total weights or 20,034 and 9275 Ibs., composed of six strands around a wire centre, each strand containing seven wires, and having a lay of about one turn in 9 inches. Third, three "cradle" ropes (to support the wooden "cradles" used as stations by the workmen adjusting the wires), three only being necessary, as one of the foot-bridge ropes serves also as a cradle rope, having a diameter of 2-1/4 in., lengths of 3625 feet, breaking strengths of not less than 180 tons, weighing 9 lbs. per foot, total weights 32,625 lbs. each; having six outer strands with nineteen wires each around a centre, the central strand being the same as the outer ones, and a lay of not less than one tnrn in 14-1/2 in. nor more than one in 15-1/2 in. These cradle ropes will be afterwards used as under-floor stays. Fourth, two "foot-bridge" ropes, scant 2-5/8 in. in diameter, one 8625 feet and the other 3688 feet long; having breaking strengths of not less than 240 tons, weighing 12 lbs. per foot, total weights 45,312 and 46,100 lbs.; composed of six strands laid around a central core, the outside strands containing nineteen wires each, the core being a regular laid rope composed of six strands and a core, eack containing seven wires, and the lay of both core and outside strands being the same, not less than one turn in 17-1/2 inches nor more than one turn in 18-1/2 inches. Fifth, four "pendulum" ropes (for separating the strands as they are made), having diameters of 11/16 in. each; being 3700 feet long, weighing 1 Ib. per foot, making 2775 lbs. weight each; composed of seven No.15 wires in each strand, with a wire centre, made in the same way as the carrier ropes, and a lay of one turn in 6-1/4 inches. These comprise all the steel ropes necessary. They are required to be of the best quality of hardened and tempered "crucible cast-steel " wire, wires made by the Bessemer, Slemens-Martin or open-hearth processes not coming within the limits of the contract. All the wire is required to have a Breaking strength at the rate of 160,000 lbs. per square inch of cross section. When tested they must stretch at least two per cent, and must have a limit of elasticity of not less than 3/8 of the breaking strength. For example, a sample of wire stretched up to 3/8 of its breakipg strength must recover itself without any appreciable permanent set. The tests are made after the wire is galvanized. As these ropes are suspended with a very slight deflection, the strain upon them is very great, arising as much from their own weight as from the load placed upon them. An increase in the size of the ropes would increase but slightly the margin of safety, and, therefore, safety depends upon quality of wire used. For the foot bridge, two galvanized iron hand-rail ropes will be used, composed of seven wires to the strand, No.17 1 gauge, having a tarred manilla core; each rope will be 3500 feet long. The under-floor foot-bridge guys will also be of galvanized iron, 11/16 of an inch, composed of six strands around a hemp centre, and having an aggregate length of 10,868 feet. Each strand is required to be composed of seven wires No.15 gauge, galvanized, and made of the best charcoal iron. The suspender chords are required to weigh 9 lbs. per foot, to consist of one strand of seven No.14 galvanized charcoal wires, and to have an aggregate length of 8000 feet. 
METHOD OF MAKING THE CABLES. On the top of the Brooklyn anchorage is stationed most of the machinery to be used in the making of the cables, It consists of two sets of identical apparatus, a description of one of which will answer for both. Fig. 1 is an elevation of the Brooklyn anchorage pier. Fig. 2, plan view of the top thereof. Fig, 3, view of the cable mechanism as arranged on the top of the anchorage pier, with the bridge pier in the distance, Fig, 4, plan and elevation showing the arrangement of the cables and foot bridge. The running or working ropes pass around a system of four grooved tension wheels, one large and three small, working in a plane paral. lel to that of the top of the anchorage. Taking in the principal drawing (Fig. 3), the apparatus on the right hand, looking towards New York, the rope (A) coming from New York, by way of the towers, passes first round the small wheel (b), then round the larger wheel (a), whence it passes back round the middle smaller wheel (0), returning in an opposite direction to the principal wheel, partly around which it again circles, and then passing around the third small wheel (d) returns towards New York. In passing over the towers the working ropes pass, coming and going, over sets of grooved cast-iron wheels set upright and revolving between large timbers bolted together and extending across the towers. The large grooved wheel (a) has a diameter of 11 ft. 6 in., and the three smaller ones have diameters of 4 ft, 3 in. each. The base of a triangle drawn through the centres of the wheels (a), (b), (0) and (d) would be 23 ft. 6 in. in length. Of the wheels on the towers, the centre one of each set has a diameter of 3 ft. and the two at the ends of 1 ft. each. The working ropes passing over the cradles run on small grooved wheels set on a frame, as at (K). The "cradle" ropes (E) and (D), (E) being a foot-bridge rope serving also as a cradle rope, pass 27 feet apart from the Brooklyn anchorage over both towers, resting simply on blocks, to the New York anchorage, where they are again secured. These ropes are to support the "cradles" as at (I), of which there are to be ten in all, 47 ft. long by 4 ft wide, disposed on the cradle ropes as follows: one on each of the two sets of cradle ropes between the towers and anchorages on both sides of the river, and three on each set of cradle ropes on the central bay, two in the middle and two on each quarter, between the towers. The "cradles", as they are termed, are long, narrow, stationary platforms of wood, resembling nothing more than the "bridge" on an ocean steamer, and are for the use of the workmen regulating the adjustment of the cable wires in their proper positions, preparatory to the strand formation. The cradJes, as mentioned above, serve as supports for running wheels over which pass the working ropes, carrying over the cradle wires as shown in the drawing. The working ropes are run by a 20 horse-power engine stationed at the foot of the anchorage, the drivinft belt (I) of which is geared on to a large spurwheel (I), to which the principal wheel of the system is fastened. A foot bridge (F), for the use of the workmen passing to and fro, is to be constructed, 8 ft. in width, and supported on two foot-bridge ropes (0) and (E). The railing ropes of the foot-bridge will be 8 ft. above the floor. The "cradle" and "foot-bridge" ropes in their final positions it is calculated will have a deflection of 78 ft. 8 in. below the crown of the masonry of the towers; a central span of 1572 ft., equivalent curve on the land sides, half span of 1313 ft. 3 in., counted 12 ft. from the centre of the tower, and a deflection of 211 ft. 1 in. The foot bridge will be guarded against lateral strain by under-floor guys attached to the towers and also between the towers and the anchorages to points on the ground beneath. To prevent confusion in the drawing, these latter are not shown. The wheels receiving the working ropes on the New York anchorage are similar to those on the Brooklyn one. On the Brooklyn anchorage, back of each system of wheels and cover of large sheds, are situated four sets of drums, one set for each cable to be made, consisting in all of thirty-two drums, or eight to each cable. These drums (see L L L L, on the principal drawing) are for holding the cable wire, are about 9 ft. in diameter by 2 ft. broad, and furnished on one side with spokes, so that the paying out of the wire can be properly regulated by men stationed at the drums for that purpose. On the 12th of August the first of the working ropes was wound upon a drum placed at the foot of the water face of the Brook]yn tower. This being finished, the free end was fastened to a rope let down from the tower, the rope then being drawn over the tower and from thence to the anchorage, where it was temporarily made fast. On the 14th of August the drum was placed on one of the stone barges, and all being ready, the barge was towed across the river by two steam tugs, the steel rope being meanwhile paid off from the drum, sinking to the bottom of the river. In eight minutes the foot of the New York tower was reached, the remainder of the rope was taken off the drum, and coiled on the pier in such a way as to leave the end of the rope on top of the coil. A hempen rope was then lowered from the top of the New York tower, and made fast to the steel one, which was then by this means raised to the top of the tower and carried over, resting on the three wheels placed there for its reception. It was then fastened to a drum worked by a fifteen horsepower engine at a rate of fifty revolutions per minute, and in two minutes was drawn over the tower. As the rope was now to be raised from the bottom of the river to its permanent position at an elevation of some 200 ft. above high tide, a steam tug warned all vessels away. On account of the immense up and down river traffic it was fully an hour and a quarter before the river was clear enough to allow of the rope being drawn up from the bottom. The drum was now attached to a thirty horse-power engine, working it at the rate of 150 revolutions per minute. In two and a half minutes the last of the wire left the water in the middle of the river, and in five minutes was swinging from New York to Brooklyn. Later in the afternoon a second wire was carried over, and now the two working ropes and one cradle rope are in their places. The principal cables used for the cable-making apparatus are lashed to a carrier rope and so drawn over, a man drawn over in a boatswain's chair, suspended from the working ropes afterwards cutting the lashings, and freeing the rope from its carrier. When every thing is ready for the commencement of operations on the rope making, an end of wire is fastened to the end of one of the anchor chains, and placed round what is known as a "carrier sheaf" (G) in the first and third drawings, which consists of a small spoked and grooved wheel with a weight attached, which, when the wire is in position, is fastened on to the working rope, and carries the doubled cable wire over, as shown in the large drawing. At each cradle the sheaf is lifted over the running wheel, which operation is also repeated at the top of the towers. On the arrival of the wire at the New York side, it is taken off the sheaf and made fast. Two sheafs are used, so that one will be coming back empty while the other is going over with the wire. When over, the wires are adjusted in the proper positions by the men stationed on the cradles, who, by means of flags and other signals, instruct the men at the drums whether to payout more or to wind in, as also the men on the towers. A full description of the various operations connected with the cable making will be given hereafter, as the work progresses. In the drawing Fig; 4, a side view of one of the towerBls seen, showing the cradle and working ropes, the line cable in process of being made, a cradle and part of the foot bridge to be used by the cradle men in going to and coming from their work. The cable is also shown in the position it will occupy when finished. The ground plan gives the position of the different ropes, including those of the foot bridge, with respect to each other and the tower. When it is said that after every thing is ready the making of the cables will occupy the greatQr past of two years, it can be seen what a gigantic operation it will be. For information and facilities the writer has to acknowledge his obligations to Mr. Hildebrandt and Colonel Payne, assistant engineers of the Bridge Company. |