Page 14 - Wire Rope News & Sling Technology - December 2018
P. 14

continued from page 12             called  “rings”)  any  of  the  unskilled   that the cutting of the threads on this
         the  object  of  this  interlocking  being   workmen could easily complete a firm   spring tempered wire called for a spe-
         to prevent uncoupling  by unscrew-  connection, which greatly accelerated   cial construction of dies, the standard
         ing while  being laid into the cables…  the work of making all those splices.   make proving an absolute failure”.
         the form of thread used, technically   The  long  term  consequences  of  V-  Due to the continuous outer wrapping
         known as a vanishing thread…was of   grooves cut into both ends of every   wire  around the  main  cables,  and  the
         the V form, or practically an equilat-  length of wire in the bridge were not   many layers of protective painting ap-
         eral  triangle  in  section,  being  at the   recognized  at  the  time.  In  his  expla-  plied since the bridge opened for busi-
         small  end  of  the  cone  the  full  size  of   nation  Brady  made  some  interesting   ness, it is nearly impossible to visually
         the standard pitch used, and tapering   observations about the wire: “Perhaps   locate one of the Brady couplings on the
         its  entire  length  to a vanishing  point   it may be of interest to some of your   exterior of the main cables to evaluate
         at the other end…It seemed to puzzle   readers to know that the wire used in   its condition as of today. During the last
         those who saw these…how the thread   the bridge cables was spring temper,   two decades of the 1800s, the sweeping
         could be so perfectly made…we made   and by the use of the vanishing thread   adoption of large volume processes for
         two conical ends alike…we also made a   above described the tensile tests   making steel stimulated  wire mills  to
         sleeve having a taper hole to perfectly   showed that none of the couplings   draw longer and longer lengths of wire
         fit the entire length of the cone”  failed  to  give  at  least  95  per  cent  of   for suspension bridges. During the same
           By simply twisting the coupling onto   the full strength of the wire and, as   time period new ways to weld lengths of
         the ends of the wire coils (which were   a whole, they averaged higher; also   wire end-to-end eliminated the need for
                                                                               couplings like Brady’s. They were never
                                                                               used again in a bridge.

                                                                               What Happens Next?
                                                                                 The wisdom of the design factor
                                                                               becomes obvious when all the risky
                                                                               aspects are added together. Although
                                                                               it was contrived to be used as a Rule-
                                                                               of-Thumb,  it  was  exactly  changing
                                                                               conditions such as these that caused
                                                                               the bridge to be built five times stron-
                                                                               ger  than  needed.  In  the  case  of  the
                                                                               Brooklyn Bridge we can add one other
                                                                               very important consideration which
                                                                               is rarely the case with other wire
                                                                               bridges. When it was built it was in-
                                                                               tended to carry horse-drawn cart and
                                                                               carriage  traffic  with  a  cable-car  sys-
                                                                               tem in the middle to transport pedes-
                                                                               trians.  The  walkway at  the  highest
                                                                               level was described as a “promenade”
                                                                               because it was intended for leisurely
                                                                               strolling. For awhile, the routing of
                                                                               heavy mass-transit trains overloaded
                                                                               the original capacity. Removing the
                                                                               heavy  railroad  traffic  and  later  the
                                                                               rerouting of heavy semi-trailers has
                                                                               reduced the burden significantly.
                                                                                 The  next most obvious adjustment
                                                                               for the future would be a change pre-
                                                                               venting  automobile  traffic  from  using
                                                                               the bridge during rush  hour,  and, at
                                                                               a later time, stopping all vehicle traf-
                                                                               fic on it except for motorcycles. Recent
                                                                               publications such as several art books
                                                                               by Richard Haw,  and Erica  Wagner’s
                                                                               Chief Engineer  have stimulated pe-
                                                                               destrian tourism  to a degree beyond
                                                                               the wildest imagination of the 1870s.
                                                                               It seems  almost incredible  to realize
                                                                               the first major design change made by
                                                                               Washington Roebling when he revised
                                                                               his father’s initial ideas was to elimi-
         The main cables of the Brooklyn Bridge have been repainted many times since the bridge   nate the sidewalks!
         opened for business in 1883. It is a visually fascinating process. The British Pathe company   Maintenance of the Brooklyn Bridge
         produced an early movie about it. You can watch it on-line; the title is “Pathe Cameramen Are
         Everywhere – Painting Brooklyn Bridge.” Next year during the planned two-year DoT exam,   and the other three East River bridges
         painters walking the cables will become a common sight. Photo by kaarsten | iStockphoto  continued on page 16
         14     Wire Rope News & Sling Technology   December 2018
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