The tower crane's base is typically bolted to a huge concrete pad that provides very necessary support. The base is connected to a tower or a mast and stabilizes the crane that is attached to the inside of the structure of the building. Often, this attachment point is to an elevator shaft or to a concrete lift.
The crane's mast is normally a triangulated lattice structure which measures 0.9m2 or 10 feet square. Attached to the very top of the mast is the slewing unit. The slewing unit consists of a motor and a gear which allows the crane to rotate.
Tower cranes are able to have a maximum unsupported height of 80m or 265 feet. The tower crane's maximum lifting capacity is 16,642 kg or 39,690 pounds with counter weights of 20 tons. Furthermore, two limit switches are utilized to be able to ensure the operator does not overload the crane. There is also one more safety feature called a load moment switch to ensure that the driver does not exceed the ton meter load rating. Lastly, the maximum reach of a tower crane is 70 meters or 230 feet.
There is certainly a science involved with erecting a tower crane, specially due to their extreme heights. First, the stationary structure has to be transported to the construction location by using a big tractor-trailer rig setup. After that, a mobile crane is used so as to assemble the machine portion of the crane and the jib. After that, these sections are connected to the mast. The mobile crane then adds counterweights. Crawler cranes and forklifts could be a few of the other industrial equipment which is usually used to erect a crane.
Mast extensions are added to the crane as the building is erected. This is how the height of the crane could match the building's height. The crane crew utilizes what is called a climbing frame or a top climber which fits between the slewing unit and the top of the mast. A weight is hung on the jib by the work crew so as to balance the counterweight. Once complete, the slewing unit is able to detach from the top of the mast. In the top climber, hydraulic rams are used to adjust the slewing unit up an additional 6.1m or 20 feet. Then, the crane operator utilizes the crane to insert and bolt into place one more mast part piece.