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A tower crane is a piece of equipment used to move or transport oversized objects. It is a stationary device, which means the base of the crane does move. A large, fixed tower supports a horizontal beam, or jib, which sits atop the tower to form an uneven letter “T.” A tower crane is often used in the construction industry to set steel beams and other large building components. It may also be used in the shipping or transportation industry to load and unload large freighters.
The base of the tower crane sits atop a concrete pad, which can vary in thickness based on the height and weight of the crane. Large anchor bolts are used to fasten the base of the tower to the concrete, and may also extend several feet into the ground. This keeps the tower safely supported to help reduce the risk of collapse.
The vertical tower extends dozens of feet into the air, and the jib rests on top. The longer section of the jib has cables attached to move or position objects below, while the shorter section of the jib extends away from these cables to act as a counterweight. Additional counterweights made from concrete or steel may be hung from the shorter section of the jib to adjust the balance of the crane.
An operator car is typically located where the jib meets the tower. The tower crane operator sits inside of this car and uses a series of controls to swing the jib and move objects. An individual on the ground or within the building oversees the process of fastening objects to the cables of the tower crane. This individual is known as a rigger, and he or she uses radio or hand signals to communicate with the crane operator.
There are two basic types of tower cranes, and they are generally categorized based on how they are constructed. A standard tower crane is assembled using a smaller supplementary crane. A self-erecting tower crane contains a hydraulic base, which forces sections of the tower up to a specified height. A secondary crane is used to attach the jib before the hydraulic mechanism is activated.
Tower cranes are often rented or leased for the duration of the project. They are known for their high cost, and also for the high number of safety precautions required to prevent collapse or injury. In very tall or complex buildings, the tower of the crane may be left in place, where it becomes a permanent part of the building. This allows builders to successfully complete a project without the risk of damage caused by trying to remove a crane from a finished building.