There are some commercial and industrial buildings which now surpass 60 stories or more. These buildings all need tall cranes to be able to help move the supplies to the upper floors. There are cranes which have their own vehicle connected or other types which are operated from the back of trucks. Tower cranes are the biggest ones on the market.
Tower cranes are the stand-alone structures which are often seen on high-rise building projects. Often, they are part of a major city's downtown skyline. Wherever new construction like apartment buildings and skyscrapers and commercial facilities such as shopping center are being constructed, chances are a crane will be on site.
Types
The two key kinds of cranes can be differentiated by the manner in which their jib or boom raises materials. The jib is the metal frame which extends from the main section. On a flat tower crane, the jib remains horizontal as it lifts things. On a luffing type 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 pounds
Body
The body of the crane is composed of a mast. This is a vertical steel frame which is a combination of individual parts. In order to increase the overall height of the machinery, parts are added. The mast extends upward to wherever the desired height is, to the control module, which is a small room that has glass windows on all four sides or to the tower as it is also called. The driver of the crane works from inside of the tower.
Lift
To raise supplies, 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 next to the control module. 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 tower's opposite side. The counter jib holds weights. These weights help to prevent the crane from toppling over when heavy supplies are lifted.