August 05: just keep spinning, just keep spinning . . .
2012/08/05 § Leave a comment
On this day in 1878 workers completed the cable spinning for the Brooklyn bridge.
The basic structural concept behind the bridge designed by John A. Roebling is very simple: a deck is suspended by vertical cords attached to four cables stretched between two great anchors and lifted by tall towers. The concept is no different than a taut laundry line with a few poles stuck in the midspan to keep it from sagging under the weight of clothes. But as in most things that are simple to explain, the fabrication and realization was anything but. The cables are the superstar of any suspension bridge, and in Roebling’s day cables had to be spun on-site and in situ; the scale and complexity of Roebling’s bridge required eighteen months of work to complete. Their production can be described with simple verbs and numerical quantities, but the truth behind this language is a heroic story. Each of the four cables, which are 3578 feet long, comprises 5434 steel wires twisted together to make a massive rope almost 16″ in diameter. All told, workers spun over 240 miles of wire into cords that they then wound into the four great cables that weigh over 866 tons each, span the river and support the bridge deck.
Perhaps the main reason the Brooklyn Bridge remains one of the most visually striking bridges in New York (or anywhere else) is the play of the massive masonry towers against its comparatively light metal wires. Nineteenth-century images that record its construction relate even more strongly how high and tall the towers were in comparison to the city. The apparent lightness of the wires and cords gives the impression that the workers floated in mid-air as they bent and spun filaments into strong cables in the creation of one of the grandest and most impressive structures in the world. The bridge remains a monument to the (literal) lengths and heights of human ingenuity, will power, and nerve.
Everyone should read David McCullough’s great book, The Great Bridge
Image: the bridge under construction (from this source)