how do they erect those large tower cranes you see on big building projects?
A tower crane is usually assembled by a telescopic jib (mobile) crane of greater reach (also see self-erecting crane below) and in the case of tower cranes that have risen while constructing very tall skyscrapers, a smaller crane (or derrick) will often be lifted to the roof of the completed tower to dismantle the tower crane afterwards
with another crane. assemble the tower first in sections, assemble the jib on the ground then lift it into place
