There are several commercial and industrial buildings which now exceed 60 stories or more. These buildings all require tall cranes to be able to help move the materials to the higher floors. There are cranes which have their own vehicle attached or other types which are operated from the back of trucks. Tower cranes are the biggest types on the market.
Tower cranes are stand-alone structures found as part of a major city's downtown skyline on high-rise building projects. When new construction such as skyscrapers or apartment buildings and commercial facilities like for instance shopping center are being built, chances are a crane would be on site.
Kinds
The two major types of cranes can be differentiated by the manner in which their boom or jib raises supplies. The jib is the metal frame that extends from the main section. On a flat tower crane, the jib remains horizontal as it carries things. On a luffing kind of tower crane, the jib could ratchet to downward or upward angles. The lifting capacity for both types can vary from 30 pounds to 10,000 pounds
Body
The crane's body is composed of a mast. This is a vertical steel frame that is a combination of separate parts. In order to increase the overall height of the machinery, parts are added. The mast extends upward to where 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 crane driver works from inside of the tower.
Lift
The crane uses a braided metal cord to be able to raise materials. This cord extends out from a motor located near the control module to the end of the boom or jib. 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 tower's opposite side. The counter jib holds weights. These weights help to prevent the crane from tipping over when raising heavy materials.