Several commercial and industrial buildings are capable of reaching heights of more than 60 stories. Obviously, while these buildings are being constructed, they need equally tall cranes to transport the supplies to the upper floors. There are cranes that have their own vehicle attached or other kinds which are operated from the rear of trucks. Tower cranes are the largest ones on the market.
Tower cranes are the stand-alone structures which are normally seen on high-rise building projects. Often, they are part of a major city's downtown skyline. Wherever new construction like for instance apartment buildings and skyscrapers and commercial facilities like shopping center are being built, chances are a crane would be on site.
Kinds
The two key kinds of cranes can be distinguished by the manner in which their jib or boom lifts supplies. The jib is the metal frame that extends from the main section. On a flat tower crane, the jib remains horizontal as it lifts items. On a luffing kind of tower crane, the jib could ratchet to downward or upward angles. The lifting capacity for both types can vary from 30 pounds to 10,000 pounds
Body
The body of the crane is composed of a vertical steel mast which is composed of separate [parts. The sections are added to increase the overall height of the machinery. The mast extends upward to where the desired height is, to the control module, that is a small room that 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
The crane uses a braided metal cord to raise materials. This cord extends out from a motor situated near the control module to the end of the jib or boom. There is a pulley system located 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 located on the opposite side of the tower. The counter jib has weights. These weights help to prevent the crane from tipping over when heavy supplies are lifted.