Some commercial and industrial buildings are capable of reaching heights of over 60 stories. Obviously, while these buildings are being built, they require equally tall cranes to be able to move the materials to the upper floors. There are cranes that are operated from the rear of trucks or other kinds that have their own vehicle connected. Tower cranes are the largest ones on the market.
Tower cranes are the stand-alone structures that are normally seen on high-rise building projects. Usually, they are part of a major city's downtown skyline. Wherever new construction like apartment buildings and skyscrapers and commercial facilities like for example shopping center are being constructed, chances are a crane would be on site.
The two key kinds of cranes can be differentiated by the manner in which their jib or boom 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 lifts items. On a luffing type of tower crane, the jib can ratchet to downward or upward angles. The lifting capacity for both kinds could range from 30,000 lbs. to 10,000 pounds
The crane's body is composed of a vertical steel mast that is composed of individual [parts. The sections are added to be able increase the overall height of the machine. The mast extends upward to wherever the desired height is, to the control module, that 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.
The crane uses a braided metal cord to be able to lift 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 which holds the cord becomes balanced by a counter jib located on the opposite side of the tower. The counter jib holds weights. These weights help to prevent the crane from tipping over when heavy materials are carried.