|HAER NY,31-NEYO,90--79 (CT)|
79. View looking north with former Brooklyn ferry slip in foreground - Brooklyn Bridge, Spanning East River between Park Row, Manhattan and Sands Street, Brooklyn, New York County, NY
|HAER NY,31-NEYO,90--75 (CT)|
75. View looking east towards Brooklyn
I read The Great Bridge by David McCullough when I was a kid. One thing I remember is that this bridge, and the Eads Bridge, pioneered using pressurized caissons to dig the holes needed for the pier foundations. Consequently, they "discovered" what we now call the bends. In fact, Washington Roebling, the son of the suspension bridge pioneer John Roebling, became bedridden early in the construction of the bridge by the bends after an inspection trip of a pier's construction. He was in a bedroom where he could see the construction from a window with a telescope and his wife, Emily, relayed his instructions to the workers. I've recently discovered the 1866 bridge at Cincinnati that was built by John Roebling.
John Roebling presented plans for the bridge in April, 1869. But Washington Roebling wrote a June 12, 1870 report because his father had died. [ReportOfChiefEngineer via Historic Bridges]
At the time of its opening on May 24, 1883, the Brooklyn Bridge was the longest spanning bridge in the world. It represents the culmination of nearly a lifetime's experience designing and building suspension structures and incorporates the pinnacle of development of design features conceived by John A. Roebling during this period. The Roebling system of suspension bridge construction became the standard for suspension bridges throughout the world. These features included the anchoring system composed of a cast-iron plate buried under masonry to which anchorage chain eyebar links were attached and rose in the curve of a quadrant, the upper ends to which were pinned the looped ends of wire cables; the method of constructing the cables where individual parallel wires were "air spun," consolidated, and wrapped with wire into a solid, cylindrical mass; the diagonal stay cables, radiating from the tower tops down to the deck, a secondary structural feature that gave partial support to the deck and also stabilized the superstructure and cable system against vertical movement in severe winds. The cables were also innovative because it was the first time that steel-wire (galvanized to protect against corrosion) was used in a bridge, and the second time that rolled-steel structural sections were used in a bridge superstructure. [HAER-data]
Fred Hadley posted four images with the comment:
Making the cables on the new East River bridge in 1902We have described from time to time, in the columns of the SCIENTlFIC AMERICAN, the four great cables which will support the massive 188-foot roadway of the new East River Bridge, and in a recent article we gave photographs showing the temporary footbridges which have been used in stringing the cables. The last of the strands has now been completed, and the four cables hung in the positions which they will permanently occupy.It would be well, therefore, before describing in detail the method of building to recapitulate some of the dimensions of these, the largest suspension cables in the world. Each cable is 18 inches in diameter and 2,985 feet in length from anchorage to anchorage.When the weight of the floor system is upon them, the cables will extend in a fairly straight line from anchorage to saddles at the top of the steel towers, where the center of the cables is 333 feet above mean high water mark in the East River, while the horizontal distance from saddle to saddle across the main span is 1600 feet.The breaking strength of each cable is 25,000 tons and their combined weight is 5,000 tons. The actual dead load which they will carry when the bridge is completed is 8,000 tons, and they are calculated to carry a maximum moving load of 4,500 tons. Each of the four cables contains 10,397 No. 8 steel wires.The specifications called for a strength of 200,000 pounds per square inch, but the actual breaking strength of the wire as determined on test, shows that the cables have an average breaking strength of 225,000 pounds per square inch; a truly marvelous result, and one which places these cables far ahead in point of tensile strength of any other structural material yet used in bridge building.One of the best features of the new cables is the very excellent system of protection against weather which has been adopted. In the first place the wire is thoroughly coated at the mills with a heavy mixture of graphite and oil, and although its greasy condition rendered it extremely disagreeable to handle, the benefit will be found in the practically indestructible nature of the work.In putting up the strands, the apportionment of labor was as follows: There were three men on each anchorage to look after the reels, put the bights on and off the carrier-wheel, splice the wires, etc. There were three men to handle the wires at the top of the tower until the strand was ready for lowering into the saddle whose duty it also was to see that the wires were hung exactly in the curve of the guide-wire already referred to.There were also three men placed between the anchorage and the top of the tower, who, as soon as the tension was adjusted, clamped the wire to the strand. The adjustment of the wire between the towers was done by seven men, and the adjustment of the wire between the other tower and the anchorage was accomplished in a similar manner to that described already.Care was taken in placing the bights of the wire around the strand-shoes to lay them in regular courses on the shoe, so that they would correspond with the position of the wires at the other end of the strand on the opposite anchorage.As each strand was completed, its end shoe was turned from the horizontal to a vertical position ami allowed to slide forward toward the tower, thereby lowering the strand to the final position of the finished cable; the shoe being finally placed in position between the anchor chain eye-bars and held in place by its end pin. The thirty-seven strands in each cable are arranged in a hexagonal cross sectional form, five strands lying on each side of the hexagon.To complete the cables it will next be necessary to place around them the clamping bands, which will form also the saddles in which the suspender cables will rest. Then the cables will be covered with protecting shields which will consist of half-round troughs of sheet steel, semi-circular in cross-section, one half of which will lie below, and the other half above the cables. Between them and the cables will be run in a hot mixture of cable preservative similar to that in which the individual wires were soaked as they were Manufactured.Scientific American, June 26, 1902
|History, p30 via Historic Bridges|
The curved tie-bars is one of the concepts that John developed during the design of his previous suspension bridges.
|History, p46 via Historic Bridges|
Making the cables by spinning many wires across the bridge and then wrapping them so that they functioned as one cable was also a significant development. Suspension bridges were originally built with tie bars and their weakness of a single-point-of-failure did cause some bridge collapses.
|History, p59 via Historic Bridges|
Before cars and trucks and after the development of electric motors, streetcars were a very important mode of transportation in a city.
|History, p67 via Historic Bridges|
|Fred Hadley posted|
Proposed endless-train loop and rotating station for an almost overloaded and “antiquated” Brooklyn Bridge in 1905
The city bridge department, knowing the bridge is loaded to near the maximum load it was designed to carry, as a cautionary measure, to prevent overloading, has made rules as to loading. At least 102 feet of empty track space must exist between every two trolley cars on the bridge, and but one elevated train on each track is permitted upon the center span at the same time. These rules are necessary, as the load on the bridge during periods of heaviest traffic is within 125 tons of the maximum load the bridge was intended to carry.
A single elevated train or a few street cars would exceed this margin of weight, and if through carelessness they should move onto the span before the train ahead has left the span, the bridge would be overloaded. If it were thus overloaded, it would not, however, be in danger of failure, because it was built with a large factor of safety. But that was twenty-two years ago. What is its factor of safety now?
The bridge department should be the best authority. During several administrations it has enforced precautionary rules. The chief engineer stated before the State Railroad Commission : "The Brooklyn Bridge is an antiquated structure, unfitted for the demands made upon it and should be rebuilt after the completion of the Manhattan Bridge within the next five years." The problem involves a combination of difficulties. The solution is to transport the people over the bridge as fast as they arrive.
The factors in the problem are: 1. Safety of passengers. 2. Weight of load on the bridge. 3. Number of persons to be transported. 4. Number of cars required. 5. Speed of cars necessary. 6. Time required for loading and unloading cars. 7. How to make the change without interrupting transportation. 8. Cost of the new system. 9. Time required to put a new system in operation. 10. A proper terminal station. Lack of cars moving over the bridge, and not lack of loading facilities, is the cause of the congestion. More cars and lighter cars is the only remedy. This forces us to a plan for special bridge cars without heavy machinery.
The system of transportation illustrated on the front page of this issue is designed to meet all the above named conditions. An endless train of cars is operated across the bridge with a circular loop at each terminus, cable traction is used, and the motors, brakes, third rails, trolley-wire supporters, wires, etc., are dispensed with.
Light trucks with small wheels are substituted for the heavy ones now used, and more than double the number of cars can be operated, without increasing the weight; and by operating them on one set of tracks we have an endless train of cars, and may increase the speed with no danger of collision. But this requires that the train shall not stop, and we are forced to use a slowly-rotating loading platform with access to it by stairways located at the center, where motion is slow.
Two cables would be used, driven by electric motors, the motors and cable in duplicate to be used on alternate days. This would reduce the danger of a "tie-up" to a minimum. The electric current could be independently generated, or purchased from power companies. This plan includes no untried feature, unless it be in the combination.
Moving sidewalks were tested at the Chicago in Paris expositions, with a difference in speed between adjoining platforms of 3 miles an hour. These cars are enclosed, and the difference in rotary speed of stairways is reduced to 1/2 mile an hour. cars without heavy machinery.
These stairways also serve as exits for arriving passengers. The loops in the endless train of cars are arranged so as to encircle about three fourths of the platforms, the cars locking with the platform edge, and rotating the platforms at the same speed as the moving train. People will then be able to step from one to the other with as much ease and safety as they now step from the parlor car to the dining car of a moving express train.
The stairways, which are attached to the platforms near the center and extend downward to near the ground, rotate with the platforms, but the motion is so slight as to be scarcely noticeable. If the platforms are made 400 feet in diameter, at twenty-miles-an-hour speed of the cars, the stairways would have a rotary speed of one mile an hour.
Beneath each stairway, and leading to it, would be an intermediate circular platform, twenty feet in diameter, on a level with the ground. It would rotate in the same direction, with a speed one half that of the stairways, or one-half mile an hour. An automatic fence prevents a person falling off the platform.
If a person failed to step off the car, moving at ten miles an hour, he would be carried over the bridge again, and back, and would lose twelve minutes; but if he did not step on the car during the first revolution of platform, he would lose but fourteen seconds, when he would begin his second revolution. He would have sixty-four seconds to step on or off the car as against twenty-eight at present. The proposed plan would reduce the load on the bridge and distribute the load more uniformly.
Roebling's report says: "I propose a speed of 20 miles an hour, as being perhaps the one most likely preferred. But this may be increased to 30 or 40 miles per hour, with absolute safety."
To render the above plan most effective, the Manhattan loop should extend over Park Row, where a curvature with a radius of 125 feet to 200 feet could be obtaIned. The Brooklyn loop could be built near Tillary Street, between Fulton and Washington Streets. This would practically connect City Hall with Borough Hall.
Scientific American excerpt, March 18, 1905