Typically the base which is bolted into a large concrete pad provides the crucial support for a tower crane. The base is connected to a mast or a tower and stabilizes the crane which is affixed to the inside of the building's structure. Often, this attachment point is to a concrete lift or to an elevator shaft.
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 that enable the crane to rotate.
Tower cranes are able to have a maximum unsupported height of 80m or 265 feet. The tower crane's maximum lifting capacity is 16,642 kilograms or 39,690 pounds with counter weights of 20 tons. In addition, two limit switches are used in order to ensure the operator does not overload the crane. There is even one more safety feature referred to as a load moment switch to make sure that the operator does not surpass the ton meter load rating. Finally, the maximum reach of a tower crane is 70 meters or 230 feet.
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 utilizing a huge tractor-trailer rig setup. Next, a mobile crane is used so as to assemble the machinery portion of the crane and the jib. After that, these sections are connected to the mast. Afterward, the mobile crane adds counterweights. Crawler cranes and forklifts could be a few of the other industrial machines which is commonly used to erect a crane.
When the building is erected, mast extensions are added to the crane. This is how the crane's height can match the building's height. The crane crew uses what is referred to as a top climber or a climbing frame which fits between the top of the mast and the slewing unit. A weight is hung on the jib by the work crew so as to balance the counterweight. When complete, the slewing unit can 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. Next, the crane driver uses the crane to insert and bolt into place one more mast section piece.