The base of the tower crane is generally bolted to a large concrete pad which provides very necessary support. The base is attached to a tower or a mast and stabilizes the crane that is connected to the inside of the building's structure. Normally, this attachment point is to a concrete lift or to an elevator shaft.
Usually, 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 minimum lifting capacity of a tower crane is 16,642 kg or 39,690 lbs. with counter weights of 20 tons. Furthermore, two limit switches are utilized in order to ensure the operator does not overload the crane. There is also one more safety feature called a load moment switch to make certain that the operator does not surpass the ton meter load rating. Lastly, the maximum reach of a tower crane is 230 feet or 70 meters.
There is certainly a science involved with erecting a tower crane, particularly because of their extreme heights. First, the stationary structure needs to be brought to the construction site by utilizing a huge tractor-trailer rig setup. Then, a mobile crane is utilized in order to assemble the equipment portion of the jib and the crane. Then, these sections are attached to the mast. The mobile crane then adds counterweights. Forklifts and crawler cranes can be a few of the other industrial equipment that is usually used 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 uses 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 can detach from the top of the mast. In the top climber, hydraulic rams are used to adjust the slewing unit up an additional 20 feet or 6.1m. Next, the crane operator utilizes the crane to insert and bolt into position another mast part piece.