Several industrial and commercial buildings can reach heights of over 60 stories. Apparently, while these buildings are being constructed, they need equally tall cranes to transport the supplies to the higher floors. There are cranes that have their own vehicle attached or other kinds that are operated from the rear of trucks. Tower cranes are the largest kinds offered on the market.
Tower cranes are the stand-alone structures which are usually found on high-rise building projects. Usually, they are part of a major city's downtown skyline. When new construction such as skyscrapers or apartment buildings and commercial facilities like shopping center are being built, chances are a crane would be on site.
There are two different types of cranes: jib crane of the boom crane. The jib is a 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 pounds to 10,000 lbs.
The body of the crane is composed of a mast. This is a vertical steel frame that is a combination of individual sections. In order to increase the overall height of the equipment, sections are added. 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 crane operator works from inside of the tower.
To lift supplies, the crane utilizes a braided metal cord. The cord extends all the way to the end of the boom or jib 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 tower's opposite side. The counter jib holds weights. These weights help to prevent the crane from toppling over when lifting heavy supplies.