Brooklyn Bridge
At the beginning of the 19th century, it is well planned to build a bridge, but … no decision is taken.
Story
It is 50 years later that John Augustus Roebling, a German emigrant, has the idea of building a bridge over the East River, a bridge now known all over the world, and which must not be missed. you are going to New York.
The Brooklyn Bridge consists of a vehicular traffic lane (in both directions), and a pedestrian walkway, above this roadway and in the center of the bridge.
The two enormous pillars of the bridge, with double Neo-Gothic arches, support a central span with an apron 486 meters long.
The anchor points that hold the steel cables supporting the bridge. Remember that the entire length of the Brooklyn Bridge is supported by four cables! … 1000 meters of pavement held by four galvanized steel cables.
The genius of the designer alone allowed to achieve this feat … and moreover, this bridge, the first steel, remained for nearly 20 years, the longest suspension bridge in the world.
So that such a weight could be supported by four cables, it was necessary to realize them to measure.
These four cables are stowed at one end of the bridge by cast iron anchor plates. Once these plates in the right place, we built around, the granite foundations that would support the end of the deck.
Each of the cables thus sealed, passes to the top of the two neo-Gothic towers high 84 meters, where it is fixed by a “balancing plate” which prevents the angle formed by the cable and the pillar, does not change with deformations due to climatic differences.
Indeed, on such a length, a lengthening of the cable would change the angle that it forms with the tower. This change (amplified by the length) would modify the tensile forces exerted on the lathes.
The “balancing plates” prevent the modification of the angle and maintain the traction exerted, absorbing a part when it changes.
Video
These two “Tours” (84 meters) are based on foundations built on the bed of the river, foundations within which it would be possible to slide four tennis courts.
The revolutionary method that Washington Roebling had learned in Europe and used to build it did not necessitate diverting the East River. It consists of working in submerged caissons inside which high air pressure is maintained to prevent flooding … so we worked at the bottom of the water but … dry!
This way of working was great. But it forced the workers to undergo a time of progressive compression before starting their work, then a decompression time after finishing it. If we knew that we had to accustom the body progressively to the stronger pressure, then, on the return to normal, and that we applied all the necessary precautions to avoid accidents, we did not yet know completely the consequences of a bad decompression.
Some accidents occurred. Punctured eardrums, but also some diseases of the caissons that create paralysis, sometimes total.
The engineer Washington Roebling, for not having taken the time to undergo a sufficient decompression, was paralyzed in a bed.
In fact, the Brooklyn Bridge is a tube made of steel beams, and, on the ceiling of this tube, is laid a footbridge for pedestrians.
The roadway for vehicles is “carried” by steel beams each weighing 4 tons. Each beam is hooked to a vertical “Suspensor”, attached to the main cable.
In addition, stays stay at the top of the towers and, obliquely, support part of the load. Then, each of these stays is hooked to, all the “suspensors” that it meets, it reinforces all the strength of the bridge, distributing the load on several points, instead of letting it practice on one.
These stays (fixed in several points), have a second function, they “pull” the pavement and stabilize it, preventing it from twisting under the action of a storm or any other terrestrial event, without preventing the deformations, deformations necessary to absorb any effort to which the bridge would be subjected (during an earthquake for example).
Brooklyn Bridge, New York, NY 10038, États-Unis
