On January 3, 1870, construction work began on the Brooklyn Bridge. While it was only briefly the longest-spanned bridge in the world (surpassed within a year by the Forth rail bridge) it has remained one of the most iconic, comparable to the Golden Gate and Tower bridges. It is today a symbol of New York and a testament to its builders, John and Washington Roebling.
John A. Roebling was already an acclaimed bridge designer when he started building the Brooklyn Bridge, having already built suspension bridges in Niagara Falls and Cincinnati. Unfortunately, he did not live to see the completion of his masterpiece, dying of tetanus poisoning a year into its construction. The Brooklyn Bridge was built in his signature neo-Gothic style, with pointed or lancet arches and brownstone masonry. At 1,594 feet long, the span was the largest he had ever designed. How was Roebling able to build such a groundbreaking structure?
For starters, the bridge’s cables were made of steel wire. Previously, iron cords or chains were used, but these were weak and heavy. The steel wires were much stronger and more efficient. Despite this, there was panic midway through construction when it was discovered that the fraudulent supplier was giving the construction team low-quality wire, and that the bridge was in danger of collapsing. John’s son Washington, then in charge of construction, rushed to adapt his plans. He did not replace the wire, but instead spun more of it into the cables. These weak wires support the bridge to this day. In the main cables alone, there are 3,700 miles of wire- enough to stretch from the bridge to Alaska.
Another structural feature that allowed such a long span is the combination of suspension and cable-stayed systems. Some cables are connected to the long suspension cables, while others are connected directly to the pylons. This provides both extra support for the span and the distinctive and beautiful weblike patterning of the cables, as seen in the picture below.
Unlike the Cincinnati and Niagara Falls bridges, the load of the Brooklyn Bridge’s main span is spread over four cables, each of which carrying a weight of 12,000 tons. That’s the equivalent of 75 average one story houses or the amount of garbage that New York City produces in a day. This was certainly a large amount of weight at the time, but a lot less than modern suspension bridges support. For instance, in Hong Kong’s Tsing Ma Bridge, the cables themselves weigh 30,000 tons and each supports a load of 117,000 tons.
Finally, the long span of the bridge has survived so long due to its deep deck, which provides stiffness and rigidity to the structure. In the 1870s, suspension bridges were regarded as weak and risky due to a slew of structural failures, where anything from wind to the rhythmic marching of soldiers tore shallow decks apart. This would still prove to be a problem seventy years later- the infamous collapse of the Tacoma Narrows Bridge. Any doubts about the safety of the Brooklyn Bridge were eliminated when P.T. Barnum led a herd of elephants, including the original “Jumbo”, across.
While there may not be much celebration this year, the 150th anniversary of its construction is quickly approaching. This would certainly be a good time to visit the city and the bridge.
What are your opinions about the Brooklyn Bridge?
Total Views: 1467 ,