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A treadwheel crane () is a , animal engine hoisting and lowering device. It was primarily used during the Roman Empire period and the Middle Ages in the building of and . The often heavy charge is lifted as the individual inside the treadwheel crane walks.
For larger weights of up to 100 t, Roman engineers set up a wooden lifting tower, a rectangular trestle support which was so constructed that the column could be lifted upright in the middle of the structure by the means of human and animal-powered capstans placed on the ground around the tower.
Generally, vertical transport could be done more safely and inexpensively by cranes than by customary methods. Typical areas of application were , Mining, and, in particular, building sites where the treadwheel crane played a pivotal role in the construction of the lofty Gothic cathedrals. Nevertheless, both archival and pictorial sources of the time suggest that newly introduced machines like treadwheels or did not completely replace more labor-intensive methods like ladders, Brick hod and handbarrows. Rather, old and new machinery continued to coexist on medieval construction sites and harbours.
Apart from treadwheels, medieval depictions also show cranes to be powered manually by with radiating , 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 are known to be in use as early as 1123.
The exact process by which the treadwheel crane was reintroduced is not recorded, although its return to construction sites has undoubtedly to be viewed in close connection with the simultaneous rise of Gothic architecture. The reappearance of the treadwheel crane may have resulted from a technological development of the windlass from which the treadwheel structurally and mechanically evolved. Alternatively, the medieval treadwheel may represent a deliberate reinvention of its Roman counterpart drawn from Vitruvius' De architectura which was available in many monastery. Its reintroduction may have been inspired, as well, by the observation of the labor-saving qualities of the Water wheel with which early treadwheels shared many structural similarities.
Contrary to a popularly held belief, cranes on medieval building sites were neither placed on the extremely lightweight scaffolding used at the time nor on the thin walls of the Gothic churches, which were incapable of supporting the weight of both hoisting machine and load. Rather, cranes were placed in the initial stages of construction on the ground, often within the building. When a new floor was completed, and massive of the roof connected the walls, the crane was dismantled and reassembled on the roof beams from where it was moved from bay to bay during construction of the vaults. Thus, the crane ‘grew’ and ‘wandered’ with the building, with the result that today all extant construction cranes in England are found in church towers above the vaulting and below the roof, where they remained after building construction for bringing material for repairs aloft.
Less frequently, medieval illuminations also show cranes mounted on the outside of walls with the stand of the machine secured to .
It is noteworthy that medieval cranes rarely featured ratchets or to forestall the load from running backward. This curious absence is explained by the high friction exercised by medieval treadwheels, which normally prevented the wheel from accelerating beyond control.
Two different types of harbour cranes can be identified with a varying geographical distribution: While gantry cranes which pivoted on a central vertical axle were commonly found at the Flemish and Dutch coastside, German sea and inland harbours typically featured tower cranes where the windlass and treadwheels were situated in a solid tower with only jib arm and roof rotating. Dockside cranes were not adopted in the Mediterranean region and the highly developed Italian ports where authorities continued to rely on the more labor-intensive method of unloading goods by ramps beyond the Middle Ages.
Unlike construction cranes where the work speed was determined by the relatively slow progress of the masons, harbour cranes usually featured double treadwheels to speed up loading. The two treadwheels whose diameter is estimated to be 4 m or larger were attached to each side of the axle and rotated together. Their capacity was 2–3 tons which apparently corresponded to the customary size of marine cargo. Today, according to one survey, fifteen treadwheel harbour cranes from pre-industrial times are still extant throughout Europe. Some harbour cranes were specialised at mounting masts to newly built sailing ships, such as in Danzig, Cologne and Bremen. Beside these stationary cranes, crane vessel which could be flexibly deployed in the whole port basin came into use by the 14th century.
A treadwheel crane survives at Guildford, Surrey, United Kingdom. It dates from the late 17th or early 18th century and formerly stood in Friary Street. It was moved in 1970, having last been used ca. 1960 to move materials for Guildford Cathedral. It is a Scheduled Ancient Monument and a Listed building.
A treadwheel crane survives at Harwich, Essex, United Kingdom. It was built in 1667 and formerly stood in the Naval Yard. It was moved to Harwich Green in 1932. The crane has two treadwheels of diameter by wide on an axle diameter. It is the only double wheel treadwheel crane in the United Kingdom. The crane is a Grade II* listed building.
() (), Gdańsk was built before 1366. It was destroyed by the soviet troops during the fighting for the city in early 1945. The brick structure survived, the wooden parts have been restored.
A reconstruction of a double wheel treadwheel crane is in use at Prague Castle, Czech Republic.
A Treadwheel Crane was used in the film Evan Almighty, when Evan complained to God that he needed a crane to construct the Ark in suburban Washington, D.C.
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