Several commercial and industrial buildings could reach heights of over 60 stories. Obviously, while these buildings are being built, they need equally tall cranes to move the materials to the higher floors. There are cranes which are operated from the back of trucks or other types that have their own vehicle connected. Tower cranes are the largest types on the market.
Tower cranes are stand-alone structures seen as part of a major city's downtown skyline on high-rise building projects. When new construction such as apartment buildings and skyscrapers and commercial facilities like shopping center are being constructed, chances are a crane will be on site.
Types
The two major types of cranes could be differentiated by the manner in which their boom or jib raises supplies. The jib is the metal frame which extends from the main section. On a flat tower crane, the jib remains horizontal as it carries items. On a luffing kind of tower crane, the jib could ratchet to upward or downward angles. The lifting capacity for both types can vary from 30,000 lbs. to 10,000 lbs.
Body
The body of the crane is composed of a mast. This is a vertical steel frame which is a combination of individual parts. In order to increase the overall height of the machine, parts are added. The mast extends upward to where the desired height is, to the control module, which is a small room which has glass windows on all four sides or to the tower as it is also called. The operator of the crane works from inside of the tower.
Lift
In order to lift supplies, the crane uses a braided metal cord. The cord extends all the way to the end of the boom or jib from a motor situated next to the control module. There is a pulley system situated at the end of the jib, through which the cord is positioned and lowered down. The jib that holds the cord becomes balanced by a counter jib situated on the tower's opposite side. The counter jib has weights. These weights help to prevent the crane from toppling over when heavy supplies are carried.