The base of the tower crane is typically bolted to a large concrete pad which provides very necessary support. The base is connected to a tower or a mast and stabilizes the crane that is connected to the inside of the building's structure. Usually, this attachment point is to an elevator shaft or to a concrete lift.
The mast of the crane is usually a triangulated lattice structure which measures 10 feet square or 0.9m2. Connected to the very top of the mast is the slewing unit. The slewing unit consists of a motor and a gear that allows 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 lbs. with counter weights of 20 tons. In addition, two limit switches are utilized in order to ensure the operator does not overload the crane. There is even another safety feature known as a load moment switch to ensure that the driver does not exceed the ton meter load rating. Last of all, the tower crane has a maximum reach of 70 meters or 230 feet.
There is certainly a science involved with erecting a tower crane, particularly due to their extreme heights. First, the stationary structure needs to be transported to the construction location by utilizing a large tractor-trailer rig setup. Next, a mobile crane is utilized in order to assemble the equipment part of the jib and the crane. Then, these sections are connected to the mast. Next, the mobile crane adds counterweights. Crawler cranes and forklifts could be a few of the other industrial equipment that is utilized to erect a crane.
When the building is erected, mast extensions are added to the crane. This is how the crane's height could match the building's height. The crane crew uses what is called a top climber or a climbing frame that 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 used to adjust the slewing unit up an extra 20 feet or 6.1m. Then, the crane operator utilizes the crane to insert and bolt into position one more mast part piece.