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continued from page 18             following the dramatic accident of the   crossing  a  bridge.  The  conclusions  of
         Chaussées asked Louis Vicat to perform   Tacoma Bridge in 1940, where this vi-  the  expert  findings  were  undisputa-
         a survey of several of these suspension   bratory phenomenon should have been   ble. The anchors of a suspension cable
         bridges. Louis Vicat, who was a “poly-  seriously considered.         broke because they were weakened by
         technicien”* engineer like Navier and   On the other hand, the technique for   corrosion, despite the lime which was
         Dufour, had become famous in 1817 for   anchoring the cable was not debated.   supposed to protect them from humid-
         the invention of artificial cement. He re-  All the experts agreed that embedding   ity inside their confinement structure.
         fused to patent this invention in order to   the cable’s anchoring  room with  lime   It  wasn’t a fabrication mistake, nor
         ensure that it remained accessible to ev-  was a good option. The anchor was not   was it a non conformity to applicable
         eryone. In 1830, he was the engineer in   inspectable, but there was (theoreti-  standards. This accident highlighted a
         charge of the construction of the Argen-  cally) no risk of corrosion. John August   failure  in  the compulsory  regulation’s
         tat Suspension Bridge over the Dordo-  Roebling agreed.               requirements.  All the bridges so far
         gne River. Louis Vicat imagined a new   At that time, Joseph Chaley was one   built were potentially dangerous.
         technique for fabricating cable directly   of several French engineers involved in   A detailed inspection of all the
         in its final position on the bridge. The   the construction of suspension bridges.   French bridges was implemented.  A
         wires were then laid in accordance with   In 1834, he built the Fribourg Bridge in   lot of them were removed, mainly be-
         the  final  curvature  of  the  cable,  and   Switzerland which, thanks to its large   cause of these inspections. This is why,
         thus naturally had the proper length.   span of 273m, retained the world record   for example, there  are no longer  any
         John August Roebling used and patent-  until 1849, when Charles Ellet, Jr. built   suspension  bridges in Paris, where
         ed this technique for the construction of   the Wheeling Bridge. In 1838 he built   at least three were built, the Arcole
         the suspension bridge over the Niagara   the Basse-Chaine Bridge in Angers.  Bridge (1828), the Bercy Bridge (1832)
         River. This technique, called “spinning”                              and the Louis Philippe Bridge (1833).
         is still used today.               THE BASSE-CHAINE ACCIDENT,         Not a single suspension bridge built in
           Charles Ellet, Jr. is an American en-  WHEN HISTORY GETS FROZEN     France before 1879 remains.
         gineer who was very interested in sus-  IN FRANCE
         pension bridges. During a survey trip   April 16, 1850, the 11th regiment of   MEANWHILE, HISTORY WAS STILL
         to France (1830  – 1831),  he visited a   light infantry was crossing the Basse-  BEING WRITTEN IN THE UNITED
         lot of bridges and took courses at the   Chaine Bridge. The weather conditions   STATES
         “Ecole Nationale des Pnts et Chaussées   were dramatically bad (rain and strong   John August Roebling and Charles El-
         – ENPC.” Later he became the repre-  winds). The bridge was oscillating un-  let, Jr. were the two main actors in the
         sentative of the French  school  in  the   der the wind action, and the men had   field of suspension bridges. Ellet, based
         United States.                     to move laterally from right to left to   on what he had learned in France, was
           Roebling agreed with the teaching at   keep their equilibrium. These motions   proposing light structures. On the con-
         ENPC, which was based on Navier’s the-  finally  amplified  the  swinging  of  the   trary, Roebling, who was convinced that
         ories, with one exception: the stiffness   bridge. When the head of the 3rd bat-  stiffness was a major issue, was propos-
         of  the  deck.  He  thought  that  the  deck   talion reached the other bank,  i.e.  al-  ing stronger and heavier structures,
         should be stiff, especially for large spans.  most all the column was on the deck,   which were more expensive.
           The accident which  occurred on the   one of the cable’s anchors broke. All the   Thus, in 1849  the contract for the
         Broughton Chain Suspension  Bridge   soldiers were thrown in the river. This   construction  of the Wheeling Bridge
         should have taken that more into con-  accident caused more than 200 deaths.  was awarded to Charles Ellet, Jr. With
         sideration. A military company of 60   The risks associated to the vibration   a span of 308 m, this bridge became the
         men found the vibration generated by   of suspension bridges had been known   largest suspension bridge in the world.
         their walk was pleasant and then tried   since  the  Broughton  accident  (1831).   A few years later, in 1854, the deck of
         to  amplify  it,  which  finally  led  to  the   After that, the  British  army ordered   this bridge suffered huge damages dur-
         collapse of the bridge. This occurred   that troops should “break step” when           continued on page 22

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