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CRANES (MACHINE HISTORY)
ORIGINS OF THE MODERN DAY CRANE
A crane is a lifting machine
equipped with a winder, wire ropes or chains and sheaves that can be
used both to lift and lower materials and to move them horizontally.
Put in basic terms, it uses one or more simple machines to create
mechanical advantage to enable the movement of loads beyond the
normal capability of a human.
The principles of operation of today's CRANE EQUIPMENT is taken for
granted, however, we thought you might be interested in learning a
bit about the history of the Crane and its development into the
modern age of technology.
CRANE
EQUIPMENT MIDDLE AGES TECHNOLOGY
 During the High Middle Ages, the tread-wheel crane
was reintroduced on a large scale after the technology had fallen
into disuse
in western Europe with the demise of the Western Roman Empire.
Generally, vertical transport was done safer and cheaper by cranes
than by customary methods.
Typical areas of application were harbours, mines, and, in
particular, building sites where the tread-wheel crane played a
pivotal role in the construction of the extremely tall Gothic
cathedrals.
An important development in crane design occurred during the Middle
Ages,
when a horizontal arm known as a jib was added to the boom. The jib
was attached to the boom in a way which allowed it to pivot,
allowing for an increased range of motion. By the sixteenth century,
cranes were built with two treadmills, one on each side of a
rotating housing containing the boom.
Apart from tread-wheels, medieval depictions also show cranes to be
powered manually by windlasses with radiating spokes, cranks and by
the
 15th century also by windlasses shaped like a ship's wheel. To
smooth out irregularities of impulse and get over "dead-spots" in
the lifting process, flywheels are known to be in use as early as
1123 AD.
Medieval cathedrals have been towering above European cities for
centuries. Their surviving construction is testimony to the
engineering capabilities of the people who built them. Taking
literally hundreds of years to build, these great Gothic buildings
and the skilful carpenters and masons responsible for their
construction are to be held in awe. The contractors on these
building sites were usually peasants of the lower class. Cathedrals
were built on old church sites throughout Europe and the world to
spread the religion of Christianity.
CRANE EQUIPMENT in the Middle Ages was used to build Europe's
cathedrals. The crane would be fixed on top of a wall as it was
being constructed and was powered by men running inside two large
wheels on each side.
A medieval crane, the same as many of its modern
counterparts, was built on site and often on the building itself.
Its function was the same as today's CRANE EQUIPMENT, to lift heavy
objects from one location to another and from one level to another
by means of a cable that extended and contracted.
Where modern and medieval CRANE EQUIPMENT differs is in the source
of power used to enable the crane to function. Medieval cranes
employed people to wind and unwind the cable. The cable was spooled
around a shaft that extended into what is best described as a "human
sized hamster wheel. The shaft rotated as a person walked either
forward or backward inside the wheel. The tread-wheel crane became
indispensible during construction of large buildings in medieval
Europe.
The medieval tread-wheel was a large wooden wheel
turning around a central shaft with a tread-way wide enough for two
workers walking side by side. While the earlier 'compass-arm' wheel
had spokes directly driven into the central shaft, the more advanced
'clasp-arm' type featured arms arranged as chords to the wheel rim,
giving the possibility of using a thinner shaft and therefore
providing a greater mechanical advantage.
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images below for larger view |
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Reconstructions of Medieval cranes |
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In contrast to modern CRANE EQUIPMENT, medieval cranes and hoists,
much like their counterparts in Greece and Rome were primarily
capable of a vertical lift, and not used to move loads for a
considerable distance horizontally as well. Because of this, lifting
work was organized at the workplace in a different way than today.
In building construction, for example, it is assumed that the crane
lifted the stone blocks either from the bottom directly into place,
or from a place opposite the centre of the wall from where it could
deliver the blocks for two teams working at each end of the wall.
Additionally, the crane master who usually gave orders to the
tread-wheel workers from outside the crane was able to manipulate
the movement laterally by a small rope attached to the load.
Slewing CRANE EQUIPMENT which allowed a rotation of
the load and were therefore particularly suited for dockside work
appeared as early as 1340.
It is noteworthy that medieval cranes rarely featured ratchets or
brakes to forestall the load from running backward. This curious
absence is explained by the high friction force exercised by
medieval tread-wheels which normally prevented the wheel from
accelerating beyond control.
Cranes were used in mediaeval ports and ship yards. The medieval
crane on the waterfront in old town Gdansk, Poland is very
interesting. Originating in the early 14th century, it unloaded
cargo from ships for centuries.
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below for larger view |
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Medieval Gantry port crane with
building overhanging in the former Hanse town of Gdansk |
Medieval port crane,
Gdansk, Poland |
Medieval port
crane, Gdansk, Poland |
Medieval port crane, Gdansk,
Poland
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Medieval port
crane, Gdansk, Poland |
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Gdansk, an ancient Baltic seaport, sits five miles up river from the
sea. The ancient cargo-hoisting tower, the Great Crane built in
1441, hangs over the river. From inside the three-story building,
workers lifted heavy cargo by pulling ropes by hand. The Great Crane
is no longer used for boat cargo, but it’s a symbol of Gdansk as a
powerful merchant port. Gdansk is situated on the
Motlawa River and the Baltic Sea. Everywhere you look in Gdansk's
Old and Main Towns are references to ships or sailing. Impressive
and impossible-to-miss is the medieval (15th century) crane that has
stood as a monument to Gdansk's importance as a port city.
The tower crane is a
modern form of balance crane. Fixed to the ground or "jacked up" and
supported by the structure as the structure is being built, tower
cranes often give the best combination of height and lifting
capacity and are used in the construction of tall buildings.
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Tower crane at the inland harbour of
Trier dates from 1774 |
Tower crane at the
inland harbour of Trier dates from 1413 |
Medieval
Tower Crane
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Medieval Tower Crane in Andernach on Rhine River,
Germany dates from 1554–1561 |
Medieval Tower Crane constructed in 1762;
1784 renovated; ruined state after 1865; 1989 reconstructed |
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Medieval Tower Crane situated in
Lüneburg, Germany.
Constructed in 1379;
reconstructed
in 1797 after ice flood |
Medieval Tower Crane situated in
Bingen, Germany. Constructed in 1487, 1819 renovated |
Medieval Tower Crane situated in Oestrich-Winkel, Germany on the
Rhine River. Constructed 1744–1745
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Medieval Tower Crane situated in
Würzburg, Germany on the Main
River. Constructed 1767–1773 |
A crane
constructed in 1742, used for mounting masts to large sailing
vessels. Copenhagen, Denmark
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According to the “present state of knowledge”
unknown in antiquity, stationary harbor cranes are considered a new
development of the Middle Ages. The typical harbor crane was a
pivoting structure equipped with double tread-wheels. These cranes
were placed on docksides for the loading and unloading of cargo
where they replaced or complemented older lifting methods like
see-saws, winches and yards.
Two different types of harbor cranes can be identified with a
varying geographical distribution. While gantry CRANE EQUIPMENT
which pivoted on a central vertical axle were commonly found on the
Flemish and Dutch coastside, German sea and inland harbours
typically featured TOWER CRANE EQUIPMENT where the windlass and
tread-wheels were situated in a solid tower with only jib arm and
roof rotating.
Interestingly, dockside cranes were not adopted in
the Mediterranean region and the highly developed Italian ports
where authorities continued to rely on the more labour-intensive
method of unloading goods by ramps beyond the Middle Ages.
Unlike construction CRANE EQUIPMENT where the work speed was
determined by the relatively slow progress of the masons, harbor
cranes usually featured double tread-wheels to speed up loading. The
two tread-wheels whose diameter is estimated to be 4 m or larger
were attached to each side of the axle and rotated together. Today,
according to one survey, fifteen tread-wheel harbor cranes from
pre-industrial times are still extant throughout Europe. Besides
these stationary cranes, floating cranes which could be flexibly
deployed in the whole port basin came into use by the 14th century.
From the Middle Ages through the 18th century, human-powered cranes
were used throughout Northern Europe for unloading heavy cargo on
docks and lifting materials at construction sites. These ingenious
mechanical devices played an important part in the economic and
social development of the cities that owned them. Cranes were often
depicted in significant etchings, paintings, and manuscripts and
were included in city maps and plans. It seems that their physical
size and their economic importance made them symbols of pride for
the trades that employed them and for the communities that benefited
from their use.
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