Page 22 - Wire Rope News & Sling Technology - June 2019
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continued from page 20
         the section slides up smoothly during
         the hydraulic jacking and does not
         bind,  stall,  or  catch.  To  accomplish
         this centering a weight, (a tower sec-
         tion is used in this case, Figure 6), is
         moved, in or out, causing the tower to
         lean one way or the other, centering
         itself to move freely. A crew member
         signals the operator when he visually
         sees the space between the two sec-
         tions are “plumb.”
           Rollers are mounted inside the
         Climbing Frame to reduce  friction
         during “jacking,” aiding in the smooth
         movement between the sections. A fa-
         tal accident in New York of a tower
         crane that was being extended showed
         damaged and broken rollers which in-
         dicated misalignment of the sections
         had caused  a binding.  An  attempt at
         re-alignment by rotating the crane
         caused the crane to fall some 200 feet
         into a busy street. (Figure 7, page 24)
           When the tower crane is being taken   Fig. 6: Centering the weight to make the two sections plumb.
         down  (disassembling)  the  process  of
         assembling is reversed. The tower is   ABUNDANT REGULATION – SMALL    with the new exposures – painfully,
         lowered by the means discussed above   IMPROVEMENT                    I’m afraid! Five major tower crane ac-
         to the elevation required so that the   Cranes that are free-standing out-  cidents killing  members of the public
         erection (assist) crane can complete the   side of the buildings next to city streets   have dramatically  affected national,
         dismantling. If the tower  was  erected   provide advantages. They’re able to   state, and local safety regulations. My
         completely using  an  assist  crane,  it   extend themselves to greater heights   2008 article “A Clamor to Regulate”
         would be dismantled in the same man-  (climb), and they work  high  over cit-  goes into detail about what occurred
         ner. In the recent Seattle accident, this   ies, but, they expose the public to fall-  and why it was unsuccessful.
         was the process that was used.     ing hazards! How did industry struggle
                                                                               REVIEW
                                                                                 As I see it, when caves for people
                                                  Fig. 5: Crawler  crane assisting  in   weren’t  convenient  or  available, hu-
                                                  the assembly of a stationary tower.
                                                                               mans started  building structures to
                                                                               keep  them dry,  warm,  and protected.
                                                                               These are the first of humankind’s ob-
                                                                               jectives, (other than eating and repro-
                                                                               duction) as far as shelters go! At first,
                                                                               people could stand on rocks  or wood
                                                                               and hand up the materials to erect
                                                                               the walls and roof. Soon, these “hand”
                                                                               methods wouldn’t suffice; and the me-
                                                                               chanical mechanisms entered into use.
                                                                                 Why  higher  and higher?  Well,  fort
                                                                               walls that were taller offered more pro-
                                                                               tection  from the enemy.  And, elegant
                                                                               soaring  vaulted cathedral arches  just
                                                                               look lovelier and make one feel better.
                                                                               In modern times it is cost effective! But
                                                                               how high is high enough?
                                                                                 The progress of the tower crane came
                                                                               from  practical  experience  and job  re-
                                                                               quirements – reacting to the work to be
                                                                               accomplished. Statistics (though some-
                                                                               times misleading) indicate that op-
                                                                               erations and erection/disassembly and
                                                                               climbing  the  tower  crane  amount  to
                                                                               about 75% of the tower crane accidents.
                                                                               Rigging and weather make up most of
                                                                               the remainder. Not many inspectors or
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