Tower Cranes are built in several distinct types.
The tower crane is a modern form of balance crane. Fixed to the ground (and sometimes attached to the sides of structures as well), or mounted on rails, the tower crane often gives the best combination of height and lifting capacity and are used in the construction of tall buildings.
The jib (colloquially, the 'boom') and counter-jib are mounted to the turntable, where the slewing bearing and slewing machinery are located. The counter-jib carries a counterweight, usually of concrete blocks, while the jib suspends the load from the trolley. The Hoist motor and transmissions are located on the mechanical deck on the counter-jib, while the trolley motor is located on the jib. The crane operator either sits in a cabin at the top of the tower or controls the crane by radio remote control from the ground. In the first case the operator's cabin is most usually located at the top of the tower attached to the turntable, but can be mounted on the jib, or partway down the tower. The lifting hook is operated by using electric motors to manipulate wire rope cables through a system of sheaves.
In order to hook and unhook the loads, the operator usually works in conjunction with a signaller (known as a 'slingger' or 'Banksman'). They are most often in radio contact, or use hand signals. The rigger directs the schedule of lifts for the crane, and is responsible for the safety of the slings and loads.
A tower crane is usually assembled by a telescopic jib (mobile) crane of greater reach (also see "self-erecting crane" ) and in the case of tower cranes that have risen while constructing very tall skyscrapers, a smaller crane (or derrick) will often be lifted to the roof of the completed tower to dismantle the tower crane afterwards.
It is often claimed that a large number of the tower cranes in the world are in use in Dubai. The exact percentage remains an open question.
There are a number of different types of tower crane;
- 'Topless saddle jib' - these have a lower profile without the tall tower and stays.
- Luffing - with jibs that lift up
- Hydraulic luffing - jib operated by a hydraulic ram.
- self erecting - semi mobile units that fold up - up to 40 m boom and 30 m under hook
- Jost - French
- Liebherr - German
- Link-Belt - American
- Pecco - American
- Potain - French
- Wolff - German / Swiss
based on a wikipedia extract
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