The tower crane's base is typically bolted to a large concrete pad which provides very necessary support. The base is attached to a tower or a mast and stabilizes the crane that is attached to the inside of the building's structure. Often, this attachment point is to an elevator shaft or to a concrete lift.
Typically, the mast is a triangulated lattice structure measuring 10 feet square or 0.9m2. The slewing unit is connected to the very top of the mast. 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. In addition, two limit switches are utilized in order to ensure the driver does not overload the crane. There is even another safety feature referred to as a load moment switch to make certain that the driver does not surpass the ton meter load rating. Finally, the tower crane has a maximum reach of 230 feet or 70 meters.
Due to their extreme heights, there is a science involved to erecting a crane. The stationary structure will at first need to be brought to the construction location by using a large tractor-trailer rig setup. After that, a mobile crane is utilized so as to assemble the equipment portion of the crane and the jib. Afterwards, these parts are connected to the mast. Afterward, the mobile crane adds counterweights. Crawler cranes and forklifts may be a few of the other industrial equipment 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 can match the building's height. The crane crew uses what is called a top climber or a climbing frame 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. 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 extra 20 feet or 6.1m. Then, the driver of the crane uses the crane to insert and bolt into place another mast part piece.