USA > New York > Kings County > Brooklyn > The civil, political, professional and ecclesiastical history, and commercial and industrial record of the county of Kings and the city of Brooklyn, N. Y., from 1683 to 1884 Volume I > Part 107
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The caissons, having been built on ways, were launched in the same manner as a ship, and were towed to the points where the piers were to be located.
The launch of the Brooklyn caisson, on March 19, 1870, was regarded as the first great step in the actual mechanical progress of the bridge. It was accom- panied by appropriate ceremonies, and witnessed by an enormous concourse of people. Meanwhile an army of workmen were busy preparing the site for the foun- dation. This comprised the establishment of a rectan- gular basin, open on the side toward the river, and sur- rounded on three sides by sheet piling, with the bottom leveled to a uniform depth of 18 feet below high water mark. Many difficulties were encountered in the work of dredging. First, the workmen took out something over 10,700 yards of surface mud. Blasting was re-
sorted to, in order to remove the boulders on the bot- tom. By April, the work had progressed so far that six air compressing machines were placed in position, ready for operations on the caisson. At the begin- ning of May the caisson was towed into position. The structure was moved by six tugboats, and the trip oc- cupied two days. Ten courses of timber were laid on the top of the caisson, crossing each other at right angles, with spaces of from four to five inches between the sticks. Within the five weeks ending with June 20, 1870 over 100,000 cubic feet of timber was thus put in place. The spaces between the timbers were filled in with concrete, for the purpose of adding the necessary weight as well as hardening and preserving the timber. Air and water shafts were put in and the finishing touches were given to the air locks. These locks were seven feet high, and six feet six inches diameter inside. The interior was lighted by bulls- eyes. Three derricks were used to lay the masonry. For the lower courses Kingston limestone was the ma- terial used, while above the surface of the river all the facing was done with granite, brought from Maine and Pennsylvania. Courses of granite blocks were laid upon the top of the caisson, by which it was sunk until it rested upon the bed of the river. Air was then forced into the chambers beneath, by means of engines upon the shore, until the water was entirely displaced, and the river bed left dry. The pressure was main- tained at this point, the engines working day and night. The air chamber was not entered and explored until May 10, 1870. The workmen obtained access to the chamber by means of two shafts which extended above the surface of the water. At the bottom of each shaft were two air locks, which were simply ante cham- bers, constructed of iron, into which the men entered from the shaft, and closing an air tight door behind them, admitted the compressed air from the caisson, by means of a cock, until the pressure in the lock reached the same degree as that in the caisson; when a communicating door was opened, and the men passed into the chamber below.
By a very ingenious arrangement which it is not necessary to describe here, the earth excavated from beneath the caisson was carried up to the surface, with- out affording opportunity for the air to escape. In this way the earth was being constantly removed from underneath the caisson, and the vast mass settled, day by day, down through the gravel and quicksand which formed the bed of the river, until, at a depth of 78 feet, on the New York side, and 45 feet on the Brooklyn side, a solid foundation was reached. In proportion as the caisson settled, the masonry upon it was built up; so that the top of the stone work was always above water. When the solid founda- tion had been reached the interior of the caisson was filled with concrete ; and the 400,000 cubic feet of tim- ber was left buried nearly so feet below the surface,
450
HISTORY OF KINGS COUNTY.
where, practicably indestructible, it remains as the foundation of the tower.
This work of lowering the caisson and removing the obstacles at the bottom required all the skill of the en- gineering corps engaged upon the bridge. The area of the wooden structure was 17,000 square feet. It was soon found that no uniform stratum could be had over the whole of this space, and it was necessary to proceed with great care. The most serious obstacle to the sink- ing of the caisson was the presence of large boulders under the edge of the iron shoe at the bottom. When they extended more than two or three feet outside the shoe, no attempt was made to haul them in, but they were chipped off until the edges of the caisson could clear them. The deeper the prospectors went, the larger and more numerous became the boulders. When the caisson had reached a depth of twenty-five feet below the water level, it became necessary to resort to blasting. Fears were entertained of the effect of the explosions upon the ear drums of the men, in view of the compressed atmos- phere, and it was apprehended that trouble might arise from injury to the air-locks and water-shafts. The ex- periment was begun by first firing a pistol with succes. sively heavier charges; small blasting charges followed, until the use of powder became an every-day resort. The descending caisson left a perpendicular wall around it, none of the soil showing any sign of caving in. In supplying the compressed air, six double air pumps were used. The air pressure at the outset was governed en- tirely by the tides, and regulated itself according to their height; but after the caisson had entered into the water-tight and air-tight strata of clay, the tides no longer had any effect upon the air pressure. Regularity of air pumping was maintained until fresh-water springs were encountered, which caused much trouble. At about this time occured some singular mishaps, which were called " blow-outs."
The overweight of the air pressure would at times disturb the equilibrium of the caisson, the structure would be moved, and the escaping air would carry an enormous stream of water up to a tremendous height. One Sunday morning, during the construction of the Brooklyn foundation, occurred the greatest blow-out in the history of the work. The overweight had increased to such an extent that the south water shaft blew out all of the compressed air. Eye witnesses state that a dense column of water, fog, mud and stones, was thrown up 500 feet into the air, accompanied by a terrific roar and a shower of falling fragments, covering the houses for squares around. This column was seen a mile off. The noise was so frightful that the whole neighborhood was stampeded, and made a rush up Fulton street. Even the toll collectors at the Ferry abandoned their tills. From this blow-out the caisson settled ten feet, its weight at the time being 17,675 tons. The air tightness was not impaired by the blow-out. Despite these mishaps, the wooden structure was steadily lower-
ed. When it had been sunk to within three feet of its bed, and while the air chamber was being filled with concrete, seventy-six brick arches were erected below it. The concrete was laid at the rate of 100 yards per day. Upon this was laid the masonry, the foundations rising as the caisson descended. Several fires occurred during the progress of the work, owing to the carelessness of workmen, and the tendency to combustion in compress- ed air. The most serious of these, in December, 1870, was not discovered for several hours after its inception, and was only extinguished by admitting air to the caisson, and then flooding the air chamber with water. The damage was confined to the third and fourth courses of timber, and by March 6, of the following year, was fully repaired, and the caisson was as strong as ever.
The following figures show at a glance the general dimensions of the Brooklyn caisson:
Length over all 168 feet.
Breadth 102 feet.
Height of air chamber 9} feet.
Total height when launched.
14} feet.
Total height when completed.
21} feet.
Cubic feet of timber in it. 111,000 feet.
Weight of iron work .. 250 tons.
Launching weight of caisson. 3,000 tons.
On the 15th of June, 1870, the first stone of the Brooklyn tower was laid ; and from that time the work went on without serious interruption. Circumstances delayed the work on the New York side, and the caisson was not launched till May 8th, 1871. It was towed to its position and the work of sinking it was commenced September 11, 1871. It may here be ob- served that the work of constructing and sinking these caissons, and building the foundations of the towers, involved some problems in engineering that had never before been practically solved. The foundation of the Brooklyn tower was sunk to a depth of forty- five feet, where a sufficiently firm foundation was found. The caisson on the New York side was sunk to the rock at a depth of seventy-eight feet. Upon the tower foundations, of course, rested the stability of the entire work, and the success of the en- terprise depended on them. By the skill of the chief engineer, W. A. Roebling, and his able assistants, Messrs. Collingwood, Paine, Martin, and McNulty, the difficulties, the risks, and uncertainties attending the construction of these foundations were satisfactorily overcome. The subsequent building of the towers, and of the superstructure, was work that had been done be- fore on a smaller scale, and involved but few problems that had not already found a practical solution.
The site selected for the New York tower was at the end of Pier No. 29, East River, 400 feet from what is denominated the shore or bulkhead lines. In its general features the New York caisson was a reproduction of that which had been used so successfully in laying the
451
THE EAST RIVER BRIDGE.
Brooklyn foundation. The air chamber, 9 feet 6 inches high, was divided into six compartments, lined with light boiler iron. The air locks were built into the roof of the caisson, and were regarded as an improve- ment upon those previously in use. There were four supply shafts. The interior was lighted with gas and calcium lights. In this caisson, as well as that of the Brooklyn foundation, measures were taken to protect the woodwork from that most destructive of insects of its kind, the teredo, or sea worm.
The caisson was equipped with a temporary floor ex- tending over the base, and additional courses of timber were laid upon it, so that when finished it contained twenty-two feet of solid timber above the roof of the air chamber. A notable part of the work of excavation below the New York caisson was the process of running the sand up through the pipes by the force of compressed air. An iron pipe was run down into the chamber, within a foot of the ground. This was supplied with a stop-cock beneath the roof. The sand and earth were heaped up around the bottom of this pipe in the shape of a cone, and when the stop-cock was opened it passed out with such great velocity that stones and gravel were often projected to a height of one hundred feet.
No brick piers were used below the caisson as in the Brooklyn air chamber .. The concrete filling was put in, and above this rose the solid mass of masonry.
By the first of June, 1872, the Brooklyn tower had reached a height of one hundred feet above high water, and the caisson of the New York tower had reached its position on the rock beneath the river bed. The filling of this caisson with concrete was completed July 12th, 1872, and in December the tower had reached the height of 57 feet. The directors failing to purchase the proper- ty for the Brooklyn anchorage, took legal steps to acquire the title to it, which was accomplished January 7th, 1873, and they at once entered on the work of clearing the ground and constructing the anchorage. This work, as well as the work on the towers, was prose- cuted till December, 1873.
The erection of the towers proceeded expeditiously, with only such delays as were caused by the non arri- val of the stone, owing to the fact that the granite was brought from different quarries, located at a great distance.
By an Act of the Legislature, passed June 5th, 1874, the entire control of the enterprise was given to the cities of New York and Brooklyn, and the private stockholders were to retire, under certain conditions which were afterward accepted.
The shares in the original company, as has been shown, were fixcd at $100 each. The list. of the subscribers, as revealed by the minute book still in the possession of the Trustees, is very interesting. It is as follows :
SUBSCRIBERS.
No. of shares.
Mayor, Aldermen and Commonalty of the City of New York. 15,000
The City of Brooklyn 30,000
Henry C. Murphy. 100
Isaac Van Anden. 200
William Marshall. 50
Seymour L. Husted.
200
Samuel McLean 50
Arthur W. Benson.
20
Martin Kalbfleisch 200
Alexander McCue. 100
William M. Tweed. 560
560
Hugh Smith.
Henry W. Slocum 500
J. S. T. Stranahan 100
50
Kingsley & Keeney
1,600
John H. Prentice. 50
William Hunter, Jr. 50
John W. Lewis
50
Total. 50,000
After the subscriptions were all made, several of the subscribers withdrew or failed to make good their promises, whereupon Mr. Kingsley took up their stock and advanced the amount necessary to cover their de- ficiencies. In fact, he, and the firm he represented, took in all over $300,000 of the entire $500,000 subscribed by the New York Bridge Company.
An estimate of the chief engineer showed that, by reason of unforeseen difficulties, and some desirable changes in the plan, the cost of the bridge would reach the sum of $13,000,000. The work, which was tem- porarily suspended in the spring of 1874, was resumed in the summer.
The Brooklyn tower was completed in the summer of 1875, and the New York anchorage was commenced. It was finished in the summer of 1876, as was also the New York tower.
The original idea of facing the towers with granite, and backing them with limestone, was adhered to throughout. As completed, they form two magnificent specimens of masonry. Better work was done on no part of the structure than upon those twin granite sen- tinels of the river.
The Anchorages .- The adoption of a suspended span of 1,595} fect, at a height of 135 feet, also deter- mincd (in combination with other mathematical and mechanical considerations) the height of the towers (2763 feet) from which the span must be suspended, and two other points in the air linc of the bridge, at which the ends of the suspension cables are securcd- in other words, the anchorages-for the cables are not to pull on the tops of the tall towers, but to rest on them with nearly a simple vertical pressure, being not cven fastened; and thus, so far from tending to pull the towers over, the suspended weight tends only to hold them in position. The cables are therefore an-
8 1 f e
Peter B. Sweeny
560
Grenville T. Jenks.
452
HISTORY OF KINGS COUNTY.
chored inland, at a distance of 930 feet back from the towers on each side.
These anchorages are solid cubical structures of stone masonry, measuring 119 by 132 feet at the base, and rising some 90 feet above high-water mark. Their weight is about 60,000 tons each, which is utilized to resist the pull of the cables. Thns anchored by their extremities on each side of the river, 930 feet back from the towers, the cables at the water-line on each side are lifted up with a long, lofty, and graceful sweep over the top of a tower 276 feet high, and droop between the two towers in a majestic curve, which one can liken to nothing else for grandeur but the in- verted arch of the rainbow.
These enormous cables are similarly supported in each case. At the bottom of the anchorage, and near its rear side from the bridge, are embedded four massive anchor plates of cast iron, one for each of the cables. These plates measure 162 by 172 feet on the face, and are 23 feet thick at the centre. The weight of each plate is over 46,000 pounds. Each plate has many radiating arms, extending to grasp the masonry in a manner suggestive of the octopns. This insures the full resistive power of the great mass of masonry upon the pull of the cables. Extending from the an- chor plates are the iron link-bars, which are abont 12 feet long, and curve in a sweep forming the arc of a circle through the solid stone work. Within 25 feet of the surface of the anchorage wall, this chain of iron links meets the wires of the cables, to which they are united. As in the towers, the backing of the granite facing of the anchorages is of limestone.
Everything was now in readiness for the engineers to enter upon the throwing of the introductory span across the East River. It was necessary, before the cable making was entered upon, that nineteen galvan- ized steel iron ropes should be thrown beyond the stream. The first carried over was known as "a traveler." Four of these were necessary at the outset. They were three-quarters of an inch in diameter, and were afterward spliced in two endless ropes around the propelling machinery. Their purpose was to assist in hauling over the other ropes and aiding generally in the construction of the cable strands. On August 14, 1876, one end of a traveler was fastened to a reel placed on a scow moored at the foot of the Brooklyn tower. It was then carried over the top of the tower and drawn up to and fastened on the Brooklyn anchor- age. Warning was given to keep the river clear. The scow was towed to the New York tower, the rope pay- ing out as she moved and sinking to the bed of the river. On the New York side it was hauled up to the top of the tower and thence over the anchorage. On the same day the second rope was taken up and hoisted into position, the ends were spliced together round the driving wheels provided, creating thereby an endless rope or pulley. The third and fourth "traveler" ropes
were lashed to the ones already in place and hauled over with the aid of steam power. . When the lashings were cut the workmen went out on the wire in suspen- ded plank seats called buggies. Next was taken over the carrier, a 14 inch rope capable of supporting a greater weight than the travelers. Then came the cradle cables to support the wooden platforms upon which the workmen regulated the spinning of the wires. The first person to cross the river on the bridge cable was Mr. E. F. Farrington, who, as the master mechanic, had charge of the cable making. He made his aerial journey on August 25, 1876.
Before the end of the year temporary cables and the cables for a foot bridge were in their places.
Making the Cables .- The machinery for manu- facturing the cables was located on the Brooklyn an- chorage. In selecting the wire to be spun in the con- struction of the cables the utmost care was taken by the engineers. The specifications were prepared with the most careful attention to detail, under the direct supervision of Col. Roebling.
The wire, after it was bronght to the yard of the Brooklyn anchorage, was dipped in linseed oil and dried, and afterwards oiled with a coating of boiled oil and rosin. The object of this process was to prevent rusting at any joints where the work of galvanizing the wires was imperfectly done. The wires were carried across the river on what was called a traveling sheave, a light wooden wheel five feet in diameter, with a grooved rim. To this sheave the end of the wire wound on the drum was attached, and as the traveler carried the sheave across the river, the wire slowly unwound and followed it. At first the wire was run out slowly, the trip from anchorage to anchorage occupying thir- teen minutes, but as the workmen became more famil- iar with their task, the time was reduced to nearly ten minutes. For months these sheaves made their rapid trips to and from the anchorages, and day by day the wires became more numerons, and the strands showed their sturdier dimensions over the river. Close upon the spinning of the wire followed the more delicate work of regulating or adjusting it to its exact place in the strand. The wires were regulated on the line of the guide-rope stretched between the towers.
Let us first imagine the cable as constructed -- simply a bunch of wires, not twisted, but laid parallel, and bound together by a continuons wrapping of wire. The wires are of size No. 7, or a little over one-eighth inch in thickness; they number over 5,000 in each cable, and make a bundle 152 inches thick. To lay and bind this prodigious bunch of wires straight and parallel, would be impossible, except by subdividing the mass into skeins or strands, which are first laid and bound sepa- rately, and afterwards united. Each cable contains 19 strands of 278 wires each. They are formed precisely like skeins of yarn or thread. Each skein is a continu- ous wire, almost exactly one million feet, or nearly 200
453
THE EAST RIVER BRIDGE.
miles in length, passing from anchorage to anchorage, back and forth, 278 times. The turns of the wire at each extremity of the skein pass around a solid block of iron, shaped externally like a horseshoc, with a groove in its periphery, in which the bend or bight of the skein lies as a skein of yarn is held on one's thumb for winding. Each shoe or eye-piece is fixed (after the strand is fin- ished) between the ends of two anchor bars, a seven-inch iron bolt passing through tlie three, and so connecting the strand with the great anchor chain at either end. After a skein is fully laid in position (passing, of course, over the tops of the towers), it is compressed to a cylindrical form at every point, by large clamp tongs, and tightly bound with wire at intervals of about fifteen inches throughout its length. The men who did this work went out for the purpose on the strand in a " buggy," so called, which is a board seat slung by ropes from the axis of a grooved wheel fitting and traveling on the strand as bound to- gether. When the strands were thus completed and duly regulated, the final work of wrapping the cable was accomplished in a similar manner.
The cables thus completed were now ready for their load, the floor or bridge proper.
The Bridge Floor .- Rising from the towers at an elevation of 118 feet above high-water mark, in gentle but graceful curve to the centre of the river span, where it meets the cables at an elevation of 135 feet above high-water mark, is the bridge floor, an immense steel frame-work, bewildering in its complexity.
Upon these enormous cables were placed the suspen- der-bands, of wrought iron, 5 inches wide and five- eighths of an inch thick; to these are attached the wire rope suspenders, and these in turn hold the steel floor beams of the roadway. These floor beams are 85 feet in length, 32 inches deep, 93 inches wide, and are sus- pended at a uniform distance of 7 feet 6 inches from centre to centre. They are unlike any beams ever be- fore used in a suspension bridge. Each beam has two top and two bottom chords, formed of steel channel bases, tied and braced together. Between each pair of the main beams lighter beams are introduced, resting on the truss chords. This cnabled the bridge builders to support and fasten the floor planking at regular in- tervals of three feet nine inches from the centers. There are six longitudinal trusses on the bridge, cx- tending its entire length. In order to give greater strength to the superstructure, smaller longitudinal trusses are placed between the floor beams. The main longitudinal trusses divide the roadway into five scc- tions, forming five avenues fenced with stcel. The outside avenues are used for vehicles, that on the North
for those going to, and that on the South for those com- ing from, New York. These outer sections have a width of nineteen feet. The central promenade, ele-
SECTION OF BRIDGE, SHOWING FOOT, RAIL AND CARRIAGE WAYS.
vated twelve feet above the roadway, is fifteen feet six inches wide, and overlooks the truss work and the rail- way intervening between it and the flanking drives, affording pedestrians a magnificent view of the river, the cities and surrounding country. The avenues be- tween the drives and the space for foot passengers are devoted to the purposes of the bridge railway system.
The weight of the whole suspended structure (cen- tral span), cables and all, is 6,740 tons,' and the maxi- mum weight with which the bridge can be crowded by freely moving passengers, vehicles, and cars is esti- mated at 1,380 tons, making a total weight borne by the cables and stays of 8,120 tons, in the proportion of 6,920 tons by the cables and 1,190 tons by the stays. The stress (or lengthwise pull) in the cables due to the load becomes about 11,700 tons, and their ultimate strength is 49,200 tons.
It will be noticed that at the centre two suspenders from each of the four cables hang close together, some- times but a few inches, sometimes more than a foot apart. This gives the clew to that problem of engi- neering and puzzle to the public, as to how the expan- sion and contraction, by heat and cold, of the floor, or bridge proper, are to be provided for. The great span may be said to be in two pieces or half lengths, con- nected at the centre by an "expansion joint." Each half of a truss is attached to one of the two suspend- ers mentioned, and the two halves are connected by plates attached to one, and sliding in channels or ways in the other. No weight comes upon these guide-plates, as the two suspenders support the halves of the truss, in- dependently of each other. The planking is so arranged as to be always continuous, and the iron rails for the cars are at this point split in half, lengthwise, so that one half plays upon the other, guide-rails on cither side protecting the cars.
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