Some commercial and industrial buildings are capable of reaching heights of over 60 stories. Apparently, when these buildings are being constructed, they require equally tall cranes to be able to move the supplies to the upper 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 offered on the market.
Tower cranes are stand-alone structures found 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 such as shopping center are being built, chances are a crane will be on site.
The two major types of cranes could be distinguished by the way in which their jib or boom raises supplies. The jib is the metal frame that extends from the main section. On a flat tower crane, the jib remains horizontal when it carries items. On a luffing kind of tower crane, the jib can ratchet to downward or upward angles. The lifting capacity for both kinds can vary from 30 pounds to 10,000 pounds
The body of the crane is composed of a mast. This is a vertical steel frame which is a combination of individual sections. In order to increase the overall height of the machine, sections are added. The mast extends upward to wherever the desired height is, to the control module, which is a small room that has glass windows on all four sides or to the tower as it is also referred to. The crane operator works from inside of the tower.
The crane uses a braided metal cord to lift materials. This cord extends out from a motor situated next to the control module to the end of the jib or boom. There is a pulley system situated at the end of the jib, through which the cord is positioned and lowered down. The jib which holds the cord becomes balanced by a counter jib located on the opposite side of the tower. The counter jib has weights. These weights help to prevent the crane from tipping over when raising heavy materials.