The base of the tower crane is usually bolted to a huge concrete pad that provides very crucial support. The base is attached to a tower or a mast and stabilizes the crane that is connected to the inside of the building's structure. Normally, this attachment point is to an elevator shaft or to a concrete lift.
The mast of the crane is normally a triangulated lattice structure that measures 10 feet square or 0.9m2. Attached to the very top of the mast is the slewing unit. The slewing unit is made of a gear and a motor which allows the crane to rotate.
Tower cranes may have a max unsupported height of 80m or 265 feet, while the tower crane's maximum lifting capacity is 16,642 kg or 39,690 lbs. with counter weights of 20 tons. Moreover, two limit switches are utilized in order to ensure the operator does not overload the crane. There is also another safety feature known as a load moment switch to ensure that the operator does not exceed the ton meter load rating. Finally, the maximum reach of a tower crane is 230 feet or 70 meters.
Because of their extreme heights, there is a science involved to erecting a crane. The stationary structure would first have to be transported to the construction site by using a huge tractor-trailer rig setup. Then, a mobile crane is used in order to assemble the machinery portion of the crane and the jib. Afterwards, these parts are attached to the mast. After that, the mobile crane adds counterweights. Crawler cranes and forklifts could be a few of the other industrial machines that is utilized to erect a crane.
Mast extensions are added to the crane when the building is erected. This is how the height of the crane is able to match the building's height. The crane crew utilizes what is called a climbing frame or a top climber 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. Once complete, the slewing unit is able to 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 driver of the crane uses the crane to insert and bolt into position another mast section piece.