There are several industrial and commercial buildings that now exceed 60 stories or more. These buildings all require tall cranes to help move the supplies to the upper floors. There are cranes that are operated from the rear of trucks or other types which have their own vehicle attached. Tower cranes are the biggest types available on the market.
Tower cranes are the stand-alone structures which are normally seen on high-rise building projects. Normally, they are part of a major city's downtown skyline. When new construction such as apartment buildings and skyscrapers and commercial facilities like for example shopping center are being constructed, chances are a crane would be on site.
Kinds
The two major kinds of cranes can be differentiated by the manner in which their boom or jib lifts materials. 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 type of tower crane, the jib could ratchet to downward or upward angles. The lifting capacity for both kinds could vary from 30,000 lbs. to 10,000 lbs.
Body
The body of the crane is composed of a vertical steel mast that is composed of separate [parts. The parts are added to be able increase the overall height of the machinery. 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 referred to. The driver of the crane works from inside of the tower.
Lift
The crane utilizes a braided metal cord to lift supplies. This cord extends out from a motor situated near the control module to the end of the boom or jib. 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 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.