Tower cranes are extensively used in building projects, specially in high rise construction sites where work concentration is in a limited area. The tower crane configuration enables the crane to be erected close to the building, and its height, enables its jib to swing clear of obstructions. These cranes have 360 degree slewing capability, and are electrically powered.
Depending upon the nature of the primary task, the tower cranes (both horizontal-jib and luffing cranes) can be grouped into the following types:
a. Stationery cranes
These are supported on foundations. Their mast is bolted to a fixed-position steel base placed on top of the foundation and their ballast counter-weight rests on the base. These cranes can go up to 100 meters in height and are mostly used for high rise buildings. The height of these cranes can be increased further by suitably bracing the mast with the structure of the building.
b. Travelling cranes
The steel base of these cranes is mounted on travel-gear, resting on rail-tracks embedded in the foundation. This enables the crane to travel along the track. The load travelling cranes can be used for constructing long buildings, and shifting heavy materials like precast elements, and batched concrete from the production site to the adjoining places or transportation areas.
c. Climbing cranes
These cranes are positioned on solid cores like the lift shaft inside a multistory building. Initially about two storys of the building are constructed by placing the crane outside the core on a selected part of the building foundation. The crane is then positioned in the core by securing it with special collars, resting on the walls of the core. Thereafter, the crane erects the building around itself, and climbs up when the mast supported on the collars is raised by winches or hydraulic jacks. Climbing cranes are economical and are specially useful where the shortage of sufficient external space around the building does not permit the erection of other tower cranes.
It may be noted that the erection of the tower cranes needs careful planning and is generally entrusted to experienced person or agencies.
