Posts tagged “Engineering

“If you believe that, I have a Bridge to sell you”

This was the original shot I was trying to execute before “Pete” jumped in the way with his sign! (See previous post)

References to “Selling the Brooklyn Bridge” abound in American culture, sometimes as examples of rural gullibility but more often in connection with an idea that strains credulity. At the time the bridge was built, the  aerodynamics of bridge building had not been worked out. Bridges were not tested in  wind tunnels until the 1950s—well after the collapse of the original Tacoma Narrows Bridge (Galloping Gertie) in 1940. (This was shown to us in University as a lesson of miscalculation, I just liked the way it was oscillatiing – perhaps this drove me to the Electrical Engineering side instead of Civil?)

It is therefore fortunate that the open truss structure supporting the deck is by its nature less subject to aerodynamic problems. Roebling designed a bridge and truss system that was six times as strong as he thought it needed to be. Because of this, the Brooklyn Bridge is still standing when many of the bridges built around the same time have vanished into history and been replaced.

This is also in spite of the substitution of inferior quality wire in the cabling supplied by the contractor  J. Lloyd Haigh – by the time it was discovered, it was too late to replace the cabling that had already been constructed. Roebling determined that the poorer wire would leave the bridge four rather than six times as strong as necessary, so it was eventually allowed to stand, with the addition of 250 cables. Diagonal cables were installed from the towers to the deck, intended to stiffen the bridge. They turned out to be unnecessary, but were kept for their distinctive beauty.