Abstract: A rotary tower crane having a tower which can be extended step-wise by adding a section between the boom supporting segment and segments of the supporting structure is provided with a host and crab mechanism for adding or removing a section adjacent to the boom without the use of another crane. The tower is provided with a movable inner tower member slidably disposed in the upper tower segment. The inner tower member has transverse members adapted to be retracted so they will pass bracing members on the tower and to expand to a point where they will support the inner member on the brace members when immediately above the brace members.

Abstract: A rotary tower crane has a tower constructed from uniformly sized sections which can be arranged to provide a tower of small or large cross section, as required. The tower sections can be aligned in a single, vertical column to provide a tower having a narrow cross section, or a plurality of sections can be joined horizontally to form sections of enlarged cross section, which are then vertically aligned to provide a tower having an enlarged cross section.