The tower crane's base is generally bolted to a large concrete pad which provides very crucial support. The base is connected to a tower or a mast and stabilizes the crane which is affixed to the inside of the building's structure. Usually, this attachment point is to an elevator shaft or to a concrete lift.
The crane's mast is often a triangulated lattice structure that measures 10 feet square or 0.9m2. Connected to the very top of the mast is the slewing unit. The slewing unit is made of a gear and a motor 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 lbs. with counter weights of 20 tons. Moreover, two limit switches are utilized to be able to make sure that the operator does not overload the crane. There is even another safety feature called a load moment switch to ensure that the driver does not surpass the ton meter load rating. Finally, the tower crane has a maximum reach of 70 meters or 230 feet.
Because of their extreme heights, there is a science involved to erecting a crane. The stationary structure will first have to be brought to the construction location by using a large tractor-trailer rig setup. Next, a mobile crane is used so as to assemble the machinery portion of the jib and the crane. Afterwards, these parts are connected to the mast. The mobile crane next adds counterweights. Crawler cranes and forklifts could be some of the other industrial machinery which is commonly 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 is able to match the building's height. The crane crew utilizes what is called a climbing frame or a top climber which fits between the top of the mast and the slewing unit. A weight is hung on the jib by the work crew in order 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 extra 20 feet or 6.1m. Next, the operator of the crane uses the crane to insert and bolt into position another mast part piece.