Page 112 - How It Works - Book of Amazing Answers To Curious Questions, 12

� AMAZIG ANSWERS TO CURIOUS QUESTIONS

Jib arm Trolley Cat head tower
The horizontal arm of a tower The trolley and hook are On hammerhead tower
crane can extend outward connected by cables to a trolley cranes, the cat head
85m. The arm has three sides motor mounted on the upper tower reinforces the jib
side of the jib arm. The operator arm and counterweight
can roll the trolley back and jib using thick steel cables
forth with hand controls. called pendants.

I Machinery
Operator's cab arm
It's a long climb to the cab, The power to raise
where the crane operator and lower the load
has a bird's-eye view of the line is supplied by a
construction site through huge winch located
floor-to-ceiling windows. along the
counterweight jib or
machinery arm.
The tower
Also known as the mast, each 2.8·metre
tower section has four sides, each with
vertical, horizontal and diagonal trusses
that give them full structural integrity.

How do cranes

Counterweights
get so high? tons - are hung or piled
Multiple concrete slabs
- each weighing several
on the very back end of
the counterweight jib to
overcompensate for the
These colossal constructions crane's lifting capacity.
are engineering marvels
Hydraulic
ower cranes flock to money. arm connects to the top of the mast. climbing
During the economic boom The magnitude and direction of this section
The hydraulic unit
T years, high-rise construction force !clockwise or anti-clockwise) is
attaches to the outside
cranes migrated from Beijing to called the moment. If the weight is Slewing unit of the tower. A powerful
Shanghai to Dubai, where it was hung close to the mast, the magnitude This motorised pivot allows hydraulic arm lifts the
entire top section of the
estimated in zoo6 that there was one of the moment is lower than if the the jib arm to rotate nearly crane just enough for
360 degrees to lift and
tower crane for every 44 residents of weight is hung far out on the jib. To drop materials all across the crane to insert a
the desert boom-opolis. keep the crane upright, the construction site. new section beneath.
Tower cranes are feats of structural counterweights are used to create a
engineering that often outshine their moment of equal magnitude in the
creations. They are designed to stand opposite direction, balancing out the
8o metres tall and reach 8o metres out rotational forces.
supported only by a narrow steel­ Once a tower crane meets its
frame mast, a concrete foundation maximum unsupported height, it can Concrete
foundation
and several counterweights. be tethered to the building itself and Large tower cranes get
The engineering principle that continue to grow with the rising their core stability by
keeps the twiggy tower crane from skyscraper. The tower cranes that rose burying the bottom of
the tower in several
tipping over is something called a with the construction of the record­ metres of concrete
'moment'. If you hang a weight from breaking Burj Khalifa skyscraper in weighing 185 tons.
the crane's jib arm, it exerts a Dubai reached a truly dizzying height
rotational force or torque where the of 750 metres.

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