There are some commercial and industrial buildings which now surpass 60 stories or more. These buildings all require tall cranes to help transport the supplies to the upper floors. There are cranes which are operated from the rear of trucks or other types that have their own vehicle connected. Tower cranes are the largest ones on the market.
Tower cranes are the stand-alone structures that are often found on high-rise building projects. Normally, they are part of a major city's downtown skyline. Wherever new construction like apartment buildings and skyscrapers and commercial facilities like shopping center are being constructed, odds are a crane would be on site.
Types
The two major types of cranes could be distinguished by the manner in which their boom or jib raises materials. The jib is the metal frame which extends from the main section. On a flat tower crane, the jib remains horizontal when it lifts things. On a luffing kind of tower crane, the jib can ratchet to downward or upward angles. The lifting capacity for both types could vary from 30,000 lbs. to 10,000 lbs.
Body
The body of the crane is composed of a mast. This is a vertical steel frame which is a combination of separate sections. In order to increase the overall height of the machinery, sections are added. 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 crane driver works from inside of the tower.
Lift
To raise materials, the crane uses a braided metal cord. The cord extends all the way to the end of the boom or jib from a motor located next to 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 that holds the cord becomes balanced by a counter jib situated on the opposite side of the tower. The counter jib holds weights. These weights help to prevent the crane from toppling over when heavy materials are carried.