Page 8 - Wire Rope News & Sling Technology - December 2018
P. 8

The Brooklyn Bridge


                                                    by Don Sayenga

         The four main cables of the Brooklyn Bridge were completed in October 1878.
         It would be another five years before the bridge went into service, but since its
         opening day on May 24, 1883, each of the four main cables has been carrying a
         load in excess of a thousand tons. Although the burden of the fabricated metal
         bridge structure they are supporting has been reconfigured several times, the
         cables themselves remain essentially as they were 140 years ago. They are unique.
         No other bridge ever has been built with the same kind of main cables. In this essay
         we’ll analyze the various considerations we should have in mind if we try to look at
         the Brooklyn Bridge as the world’s oldest and largest experiment in metal fatigue.

              he phenomenon called “metal fa-  adopted a very simplistic engineering   all  kinds  of  political connections  plus
              tigue” is a weakened condition in-  approach originally called the “Safety   he  controlled  the  city’s  leading news-
         Tduced into metallic structures by   Factor”. Today it is known as the Design   paper. He also gave himself the con-
         repeated stresses or loadings. It causes   Factor. For ordinary mechanical and   tract to build the eastern  anchorage.
         metals  to  fail at much  weaker  stress   civil engineering it is Six-to-One.  Brooklyn was the 3rd largest city in the
         than originally predicted. According to   In reality, the Brooklyn  Bridge was   USA at the time (after New York City
         on-line Encyclopedia Britannica, it in-  built  by contractors  and  subcontrac-  and Philadelphia) which made it very
         volves a number of physical changes in-  tors. The general superintendent was   important  to Kingsley that all of the
         cluding atomic slip, crack initiation, and   William Kingsley who was the primary   Brooklyn Bridge main cable wire ought
         crack  propagation.  When  it  was  first   promoter for the whole enterprise.  A   to be made right there in Brooklyn. It
         recognized by European scientists, they   wheeler-dealer in Brooklyn, he had           continued on page 10

         Commuters walk and cycle across Brooklyn Bridge every day in winter.  Photo by Kirkikis |
         8      Wire Rope News & Sling Technology   December 2018
   3   4   5   6   7   8   9   10   11   12   13