Page 20 - Wire Rope News & Sling Technology - June 2019
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continued from page 18
         fied, and at a rapid pace it seems.
           Older  towers  were  single  section
         towers,  but soon  construction  needed
         multi-sections  that were  pinned or
         bolted together to increase the height
         that loads could be lifted. These old
         designs became useless for most build-
         ings over three floors.
           A change (in the 1970/1980s or so) to
         start relocating the tower from inside
         the  elevator  shaft  (where  the  floors
         stabilized the tower) to the outside of
         the building’s perimeter, ended up,
         as it turns  out,  increasing  accident
         exposures  to the  public  in  the  streets
         around the construction  site. Moving
         the crane’s  location affected two ele-
         ments of the crane’s design; a longer jib
         was necessary to reach all the corners
         of  the structure  and tie-backs  to the
         building were required for tower sup-
         port. (Figure 3.)
           However, this move did open up the
         elevator shaft that the towers once oc-
         cupied, thus,  allowing  work  to take
         place in that area at the same pace as
         the  building’s  general  progress.  Was
         the trade-off for the opening of the
         elevator shafts worth it? Sure,  if the
         falling of tower cranes can stop! Now,
         occurring  accidents bring to light the
         problems of the modern tower.                                                      Fig. 3: Tower crane and jib.
           Another evolving change came when                                                Photo © lvinst | iStockphoto
         crawler cranes, equipped with a tower
         attachment and luffing jibs (Figure 4)   became the assist cranes and were   However, in congested urban areas,
         that could safely work  at about 250   used to assemble the stationary tower   alongside busy streets and hundreds of
         feet, were replaced with the fixed tower   crane  to  the height possible.  (Figure   feet in the air, it’s worst. Here, if things
         crane  erected on site (much  cheaper).   5, page 22) Moreover, these new mag-  go wrong, members of the public are at
         These specially equipped mobile cranes   nificently designed tower cranes could   risk. Not to put a price on human life,
         were used to build the structures them-  raise  (climb) themselves as well  – to   but killing an innocent member of soci-
         selves and still do. When greater build-  more than 1500 feet.        ety is much more expensive than kill-
         ing height was needed, crawler cranes    Any crane work requires caution.   ing an employee: the former is liability
                                                                               litigation, and the latter is statutory
                                                                               workers’ compensation.

                                                                               ERECTING, JUMPING, AND
                                                                               DISMANTLING
                                                                                 In the years between 1989 and 2008
                                                                               major tower crane accidents involving
                                                                               bystanders were broadcast through
                                                                               the country and still can be viewed
                                                                               on the  internet. Investigating their
                                                                               causes produced increased awareness
                                                                               by designers and in erection meth-
                                                                               ods. About 32% of the accidents occur
                                                                               when the crane is being erected, dis-
                                                                               assembled or extended, called “climb-
                                                                               ing or jumping.”
                                                                                 The  climbing  procedure  will  go  as
                                                                               expected if the crew properly per-
                                                                               forms the method’s particulars! The
                                                                               “particulars” are that the section be-
                                                                               ing inserted is centered between the
                                                                               sides of the “Climbing Frame” and
                       Fig. 4: Crawler crane equipped with a tower attachment.
                                                                                                continued on page 22
         20     Wire Rope News & Sling Technology   June 2019
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