Monday, 5 January 2009


The Brooklyn Bridge was by far the longest suspension bridge in the World With a central span of 1600 feet, it was 60% longer than its nearest rival - the 1000 foot Cincinnati Bridge spanning the Ohio River. Th length of the bridge wasn't the only issue either, it was the foundation also. By definition, the roadway of a suspension bridge is suspended by wires from the towers above it, towers which therefore require an extremely solid foundation.

The bottom of the East River is sand - totally unfit to support the necessary weight of the towers - and at the time no one knew how far down the sand went. The Cincinnati Bridge, also constructed by the Roebling family, was easy. Its foundation is barely knee-deep in water, in contrast with the Brooklyn Bridge, which would be laid 40-80 ft. deep. The problem of the laying the foundation in such deep water was solved by using "caissons", massive wooden boxes (3000 tons each for the two Brooklyn Bridge towers), built air-tight, and floated down to where the foundation was to be dug. Stone was then layered on them until they sunk to the bottom of the river.

Cut-away diagram of a Caisson rising out of the East River

The water was pumped out with compressed air, and workers could begin excavating the riverbed until they reached bedrock. Danger increased exponentially with each meter of depth. Fires, explosions and "caisson disease" - now known as nitrogen narcosis, or 'the Bends' - took the lives of 20 men, and left Chief Engineer Washington Roebling paralyzed. On the Brooklyn side, the bedrock was found at 45 feet but on the Manhattan side, they never did hit bedrock. At 78 feet, Roebling decided that the weight of the tower would be enough to hold it in place. Only then did the men begin to build their way, brick by brick, back to the surface.

Inside the Caisson
Life in the caisson was miserable. E.F.Farrington, the master mechanic working under Washington Roebling, described the inner workings of the caissons as follows:
"Inside the caisson everything wore an unreal, weird appearance. There was a confused sensation in the head, like "the rush of many waters." The pulse was at first accelerated, then sometimes fell alarmingly below the normal rate. The voice sounded faint unnatural, and it became a great effort to speak. What with the flaming lights, the deep shadows, the confusing noise of the hammers, drills and chains, the half-naked forms flitting about, if of a poetic temperament, get a realizing sense of Dante's inferno. One thing to me was noticeable - time passed quickly in the caisson."
The next time your breath is being taken away, from admiring the magnificently beautiful sight that is Brooklyn Bridge, please spare a thought for the poor devils who risked life, limb and sanity by working in the caissons, for without their efforts there would not be a Brooklyn Bridge.

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