“A San Francisco cable car holds 60 people…” So began the year end summary of my blog’s reader traffic sent to me by WordPress, the site that hosts the CloudCalc blog. “Your blog was viewed 1,900 times, by visitors from 69 different countries, in 2014. If it were a cable car, it would take about 32 trips to carry that many people.”
I thought it was a strange analogy for a blog — a cable car. To many, a blog is “high-tech”, something that reaches out and connects the world, while the cable car is a relic of the past, a quaint artifact of the days when humankind was still learning to overcome the barriers of nature. But then I started thinking about it a little deeper and it began to make sense: roughly 150 years ago the iron/steel cable (or more accurately “wire rope”) was high tech itself, and was much more responsible for connecting many parts of this country. Largely responsible for introducing that wire rope, and providing its use in connecting America, was one of the great engineering families – the family of John Augustus Roebling.
Today it is hard to believe that just a 150 years or so ago the growth of this country was held hostage to physical barriers such as mountains and rivers. Sure, some canals and railroads had been built, but in many places land transportation was powered by muscle and rope, and many rivers were too wide to be crossed by anything other than boats. Especially difficult to fathom was that the fact that New York, our nation’s largest city was located on an island, with severely restricted access to its neighbors. The bodies of water that surrounded harbor cities such as New York were double-edged swords – they allowed for the city to grow due to inexpensive water transportation along the Hudson River or from across the ocean, but constricted local growth and communication due to lack of cost-effective access to the immediate environs of New Jersey or Brooklyn. This sort of restriction was prevalent throughout the continent – railroads and canals may have carried a great many goods and people, but once they encountered rivers or high mountains, the link was broken and these goods and people had to transfer to boats, rope drawn cable cars, or other inefficient means of transportation in order to continue their trips.
The means of overcoming this was born in the 1841 in Saxonburg, Pennsylvania. The nearby Allegheny Mountains represented a major barrier to the growing country – canal boats and railroad cars had to be hauled over the mountains using hemp ropes – ropes that were expensive to make and which wore out quickly. John Augustus Roebling, a Prussian immigrant trained as an engineer in his native country, got the idea that twisting iron wire together could create a stronger, more durable rope to replace the hemp. He began making the wire rope by hand on his farm and became successful enough selling it that he soon was able to open a wire rope factory in Trenton, NJ.
Availability of wire rope made the construction of long suspension bridges possible, and Roebling – putting to use his bridge engineering studies from back in Prussia — became their preeminent designer/constructor. His initial 20 foot long demo bridges in Trenton led to bridges throughout Pennsylvania (with lengths up to 190 feet), across the Niagara River at Niagara Falls (820 feet), and finally in 1866 across the Ohio River at Cincinnati (1,057 feet long), many of which are still in use today. Finally humankind was beginning to overcome the limitations previously imposed by nature.
In 1867 he began to work on the design of the bridge that would capture the imagination of the country – the Brooklyn Bridge. Completion of this bridge, with a free span of 1595 feet, would not only top the length of the previous longest suspension bridge by nearly 60%, but would also provide a major “land” link to the nation’s largest city.
But there was still a long way to go before John Roebling’s design culminated in the opening of the bridge in 1883, and it would take two more Roeblings to see it through. John Roebling’s life was cut short via a freak accident – his toes were crushed by a ferry while checking out sites for his bridge and he died of tetanus shortly thereafter. Before dying he appointed his son Washington to the job of Chief Engineer with the responsibility to oversee completion of the original design.
Washington Roebling proved to be nearly as great an engineer as his father. The construction of the Brooklyn Bridge required significant innovation in the use of caissons to permit underwater construction, and Roebling invented much of that technology, often through trial and error experimentation within the caissons themselves. It was during one of Roebling’s visits to the caissons in 1870 that he contracted the bends, which so destroyed his health that he was forced to retire to his nearby apartment, almost never to visit the bridge site again. From 1870 to 1883 Washington Roebling supervised the construction of the Brooklyn Bridge in absentia, which brings us to possibly the most intriguing member of the Roebling family of engineers.
Emily Warren Roebling, Washington’s wife, was not formally trained as an engineer (as no women could be at that time), but one could not say that she wasn’t game. After all, her honeymoon had consisted of a European tour spent investigating European caisson technology. Once Washington fell ill, Emily became his sole connection to the project, serving as his liaison to the site, and, as acting Chief Engineer, supervised the daily construction at the bridge. In order to carry out this work Washington taught Emily all he knew about structural engineering – mathematics, strength of materials, stress analysis, cable construction…and it was her doing that saw the project through. In recognition of this fact, Emily Roebling was actually given top billing on the plaque erected in honor of the bridge’s builders.
Despite the fact that the nation had long previously crossed a continent, the crossing of the relatively narrow East River in New York was celebrated in an unprecedented manner, because all understood that this was a confirmation that man had finally conquered nature. From here on, there would be no physical boundaries too great. The extended Roebling family kept their fingerprints on the infrastructure expansion, as cables from their Trenton factory went on to power the San Francisco cable cars and tram cars constructing the Panama Canal, as well as to support most of the great suspension bridges of the United States – the Williamsburg, George Washington, Golden Gate, and many more.
Building your own bridge? Get the whole family involved, and why not use www.cloudcalc.com — Structural Analysis on the Cloud.
PS: I would like to thank all 1900 readers who checked out the 17 postings since August 2014 – I hope you continue to find a reason to come back, read, and comment!
By Tom Van Laan
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