The base of the tower crane is usually bolted to a huge concrete pad which provides very necessary support. The base is connected to a mast or a tower and stabilizes the crane which is connected to the inside of the structure of the building. Usually, this attachment point is to an elevator shaft or to a concrete lift.
Usually, the mast is a triangulated lattice structure measuring 0.9m2 or 10 feet square. The slewing unit is connected to the very top of the mast. The slewing unit consists of a motor and a gear which allows the crane to rotate.
Tower cranes may have a max unsupported height of 80m or 265 feet, while the minimum lifting capacity of a tower crane is 16,642 kg or 39,690 pounds with counter weights of 20 tons. In addition, two limit switches are utilized to be able to ensure the operator does not overload the crane. There is also one more safety feature known as a load moment switch to ensure that the driver does not exceed the ton meter load rating. Lastly, the tower crane has a maximum reach of 230 feet or 70 meters.
There is definitely a science involved with erecting a tower crane, particularly due to their extreme heights. At first, the stationary structure has to be transported to the construction site by using a large tractor-trailer rig setup. Then, a mobile crane is utilized so as to assemble the equipment portion of the jib and the crane. Afterwards, these parts are attached to the mast. The mobile crane next adds counterweights. Crawler cranes and forklifts may be a few of the other industrial machines which is typically utilized 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 uses 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 in order to balance the counterweight. When complete, the slewing unit can detach from the top of the mast. In the top climber, hydraulic rams are used to adjust the slewing unit up an extra 6.1m or 20 feet. Then, the operator of the crane uses the crane to insert and bolt into place one more mast section piece.