The base of the tower crane is usually bolted to a big concrete pad which provides really necessary support. 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. Normally, this attachment point is to an elevator shaft or to a concrete lift.
The mast of the crane is often a triangulated lattice structure that measures 0.9m2 or 10 feet square. Connected to the very top of the mast is the slewing unit. The slewing unit is made of a motor and a gear 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 kg or 39,690 lbs. with counter weights of 20 tons. In addition, two limit switches are utilized to be able to make sure that the driver does not overload the crane. There is also another safety feature called a load moment switch to ensure that the driver does not surpass the ton meter load rating. Lastly, the tower crane has a maximum reach of 230 feet or 70 meters.
There is definitely a science involved with erecting a tower crane, particularly due to their extreme heights. At first, the stationary structure needs to be transported to the construction location by utilizing a huge tractor-trailer rig setup. After that, a mobile crane is utilized in order to assemble the machinery part of the crane and the jib. These parts are then connected to the mast. After that, the mobile crane adds counterweights. Crawler cranes and forklifts may be some of the other industrial machines which is usually used 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 utilizes what is known as a climbing frame or a top climber 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 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. Then, the crane operator uses the crane to insert and bolt into place one more mast section piece.