Tower cranes are a common fixture at any major construction site. They're pretty hard to miss -- they often rise hundreds of feet into the air, and can reach out just as far. The construction crew uses the tower crane to lift steel, concrete, large tools like acetylene torches and generators, and a wide variety of other building materials.
Parts of a Tower CraneAll tower cranes consist of the same basic parts:
The base is bolted to a large concrete pad that supports the crane.
The base connects to the mast (or tower), which gives the tower crane its height.
Attached to the top of the mast is the slewing unit -- the gear and motor -- that allows the crane to rotate:
The base is bolted to a large concrete pad that supports the crane.
The base connects to the mast (or tower), which gives the tower crane its height.
Attached to the top of the mast is the slewing unit -- the gear and motor -- that allows the crane to rotate:
On top of the slewing unit are three parts:
The long horizontal jib (or working arm), which is the portion of the crane that carries the load. A trolley runs along the jib to move the load in and out from the crane's center:
The long horizontal jib (or working arm), which is the portion of the crane that carries the load. A trolley runs along the jib to move the load in and out from the crane's center:
The shorter horizontal machinery arm, which contains the crane's motors and electronics as well as the large concrete counter weights:
The operator's cab:
The machinery arm contains the motor that lifts the load, along with the control electronics that drive it and the cable drum, as shown here:
The motors that drive the slewing unit are located above the unit's large gear:
Why Don't They Fall Over?When you look at a tall tower crane, the whole thing seems outrageous -- why don't these structures fall over, especially since they have no support wires of any kind?
The first element of the tower crane's stability is a large concrete pad that the construction company pours several weeks before the crane arrives. This pad typically measures 30 feet by 30 feet by 4 feet (10 x 10 x 1.3 meters) and weighs 400,000 pounds (182,000 kg) -- these are the pad measurements for the crane shown here. Large anchor bolts embedded deep into this pad support the base of the crane:
The first element of the tower crane's stability is a large concrete pad that the construction company pours several weeks before the crane arrives. This pad typically measures 30 feet by 30 feet by 4 feet (10 x 10 x 1.3 meters) and weighs 400,000 pounds (182,000 kg) -- these are the pad measurements for the crane shown here. Large anchor bolts embedded deep into this pad support the base of the crane:
So these cranes are essentially bolted to the ground to ensure their stability. In the next section, you'll learn how tower cranes "grow."
SLIDESHOW:
safety features. past and present accidents
how much weight can a tower crane lift
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