The base of the tower crane is usually bolted to a large concrete pad which provides really necessary support. The base is attached to a tower or a mast and stabilizes the crane that is connected to the inside of the structure of the building. Normally, this attachment point is to an elevator shaft or to a concrete lift.
Generally, 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 is made of a motor and a gear which enable 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. Additionally, two limit switches are used to be able to make certain that the driver 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 230 feet or 70 meters.
There is certainly a science involved with erecting a tower crane, especially due to their extreme heights. At first, the stationary structure has to be brought to the construction location by using a huge tractor-trailer rig setup. Next, a mobile crane is utilized in order to assemble the equipment part of the crane and the jib. After that, these parts are attached to the mast. The mobile crane then adds counterweights. Crawler cranes and forklifts may be a few of the other industrial machinery that is utilized to erect a crane.
When the building is erected, mast extensions are added to the crane. This is how the crane's height is able to match the building's height. The crane crew utilizes what is known as a top climber or a climbing frame that 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. When complete, the slewing unit could detach from the top of the mast. In the top climber, hydraulic rams are utilized to adjust the slewing unit up an additional 20 feet or 6.1m. Then, the operator of the crane uses the crane to insert and bolt into place another mast part piece.