Typically the base which is bolted into a large concrete pad provides the essential support for a tower crane. The base is connected to a mast or a tower and stabilizes the crane that is attached to the inside of the building's structure. Often, this attachment point is to a concrete lift or to an elevator shaft.
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 tower crane's maximum lifting capacity is 16,642 kilograms or 39,690 pounds with counter weights of 20 tons. Moreover, two limit switches are used in order to ensure the driver 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. Lastly, the maximum reach of a tower crane is 70 meters or 230 feet.
Due to 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 big tractor-trailer rig setup. Then, a mobile crane is used so as to assemble the machine portion of the jib and the crane. These parts are then connected to the mast. Then, the mobile crane adds counterweights. Crawler cranes and forklifts may be a few of the other industrial machines that is typically 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 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 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 crane operator uses the crane to insert and bolt into place another mast section piece.