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 connected to the inside of the building's structure. Often, 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 consists of a motor and a gear that 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 kilograms or 39,690 pounds with counter weights of 20 tons. Moreover, two limit switches are utilized to be able to make certain that the driver does not overload the crane. There is also one more safety feature referred to as a load moment switch to make certain that the driver does not surpass the ton meter load rating. Last of all, the tower crane has a maximum reach of 70 meters or 230 feet.
There is definitely a science involved with erecting a tower crane, especially because of their extreme heights. At 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 machinery 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 machinery which is typically 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 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 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 extra 20 feet or 6.1m. After that, the crane driver utilizes the crane to insert and bolt into position one more mast section piece.