There are several industrial and commercial buildings which now exceed 60 stories or more. These buildings all need tall cranes to be able to help transport the supplies 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 biggest types offered on the market.
Tower cranes are the stand-alone structures which are usually seen on high-rise building projects. Often, they are part of a major city's downtown skyline. When new construction like skyscrapers or apartment buildings and commercial facilities like shopping center are being built, odds are a crane will be on site.
Types
The two major types of cranes can be distinguished by the way in which their boom or jib raises materials. The jib is the metal frame that 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 can ratchet to upward or downward angles. The lifting capacity for both kinds can range from 30,000 lbs. to 10,000 lbs.
Body
The body of the crane is composed of a vertical steel mast which is composed of individual [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, 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
In order to raise materials, the crane uses a braided metal cord. The cord extends all the way to the end of the jib or boom from a motor located near the control module. 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 has weights. These weights help to prevent the crane from toppling over when heavy materials are lifted.