Suspension Bridges tie road networks together over bodies of water. The longest in the world currently is over 12,000 feet long.
Suspension Bridges
The concept of suspension bridges goes back a long way and the name could justly be applied to many rope bridges, from those built by the Inca to similar structures thrown up around the globe by British Army Engineers, but today the name is usually applied to steel cable suspension bridges. Engineer John A. Roebling pioneered this idea for use on his masterpiece, the Brooklyn Bridge. Unfortunately he died of tetanus before construction ever began and the vision was carried through by his son Washington Roebling. The son suffered much in the execution of this vision. Descent into the deep caissons built to set the bridge pilings in the riverbed resulted in painful and debilitating attacks of a disease they named “caisson disease” a phenomenon that would later be known as the bends. Not only the engineer, but numerous workers on the bridge project suffered from this disease. Roebling oversaw much of the construction from a bed in his apartment using a telescope and relayed messages.
Despite these and numerous other hardships, and the then astronomical sum of $18 million spent, the bridge was complete in 1883 after 14 years of construction. It spanned 3460 feet, was the world’s first steel cable suspension bridge, and connected the island of Manhattan with Brooklyn. Overall the bridge project was a huge success, and ushered in a new era in bridge engineering. Many shorter steel cable suspension bridges would be built, and some longer, but few would ever rival the Brooklyn Bridge for fame.
One that does is the Golden Gate Bridge in San Francisco. Spanning 8,981 feet, frequently challenged by high winds, and standing in a known earthquake zone, this is truly a marvel of engineering. Maverick engineer Joseph Strauss undertook this monumental task, and the bridge was completed in 1937 at a cost of $27 million. The radical design employed hundreds of tons of concrete poured into a coffer damn bigger than a football field and deep anchorages on the southern shore. The bridge employs enough steel cable to circle the Earth three times. For quite some time this seemed like a feat that could not be topped.
But in 1998 Japanese engineers completed the 12,828 foot Akashi Kaikyo. This giant bridge is longer than four Brooklyn Bridges, and employs enough steel cable to encircle the Earth seven-and-a-half times. It is built with wind dampers to defeat standing waves that are a threat to suspension bridges, and is built to withstand 180 mph winds. It is also designed to withstand earthquakes up to 8.5 on the Richter scale. One secret of this monumental design is trusses beneath the roadway allowing longer spans by using triangular geometric shapes to reinforce each other and tie the cables to.
Like other great suspension bridges the Akashi Kaikyo will almost certainly be topped at some point in the future, but for now it stands as the longest suspension bridge in the world, and as a monument to human ingenuity.
