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Diagram of a modern crawler crane withoutriggers. Thelatticed boom is fitted with ajib.Manual crane from the late 19th century used for unloading small loads from ships at the Port of Barcelona, Spain
Acrane is amachine used to move materials both vertically and horizontally, utilizing a system of aboom,hoist,wire ropes orchains, andsheaves for lifting and relocating heavy objects within the swing of its boom. The device uses one or moresimple machines, such as thelever andpulley, to createmechanical advantage to do its work. Cranes are commonly employed in transportation for the loading and unloading of freight, inconstruction for the movement of materials, and in manufacturing for the assembling ofheavy equipment.
The first known crane machine was theshaduf, a water-lifting device that was invented in ancientMesopotamia (modern Iraq) and then appeared inancient Egyptian technology. Construction cranes later appeared inancient Greece, where they were powered by men or animals (such as donkeys), and used for the construction of buildings. Larger cranes were later developed in theRoman Empire, employing the use of humantreadwheels, permitting the lifting of heavier weights. In theHigh Middle Ages, harbour cranes were introduced to load and unload ships and assist with their construction—some were built into stone towers for extra strength and stability. The earliest cranes were constructed from wood, butcast iron,iron andsteel took over with the coming of theIndustrial Revolution.
For many centuries, power was supplied by the physical exertion of men or animals, although hoists inwatermills andwindmills could be driven by the harnessed natural power. The firstmechanical power was provided bysteam engines, the earlieststeam crane being introduced in the 18th or 19th century, with many remaining in use well into the late 20th century.[1][2] Modern cranes usually useinternal combustion engines orelectric motors andhydraulic systems to provide a much greater lifting capability than was previously possible, although manual cranes are still utilized where the provision of power would be uneconomic.
There are many different types of cranes, each tailored to a specific use. Sizes range from the smallest jib cranes, used inside workshops, to the tallest tower cranes, used for constructing high buildings. Mini-cranes are also used for constructing high buildings, to facilitate constructions by reaching tight spaces. Large floating cranes are generally used to buildoil rigs and salvage sunken ships.[citation needed]
Some lifting machines do not strictly fit the above definition of a crane, but are generally known as cranes, such as stacker cranes and loader cranes.
Greco-RomanTrispastos ("Three-pulley-crane"), a simple crane type (150 kg load)
A crane for lifting heavy loads was developed by theAncient Greeks in the late 6th century BC.[8] The archaeological record shows that no later than c. 515 BC distinctive cuttings for both lifting tongs andlewis irons begin to appear on stone blocks of Greek temples. Since these holes point at the use of a lifting device, and since they are to be found either above the center of gravity of the block, or in pairs equidistant from a point over the center of gravity, they are regarded by archaeologists as the positive evidence required for the existence of the crane.[8]
The introduction of thewinch andpulley hoist soon led to a widespread replacement oframps as the main means of vertical motion. For the next 200 years, Greek building sites witnessed a sharp reduction in the weights handled, as the new lifting technique made the use of several smaller stones more practical than fewer larger ones. In contrast to thearchaic period with its pattern of ever-increasing block sizes, Greek temples of the classical age like theParthenon invariably featured stone blocks weighing less than 15–20 metric tons. Also, the practice of erecting large monolithic columns was practically abandoned in favour of using several column drums.[9]
Although the exact circumstances of the shift from the ramp to the crane technology remain unclear, it has been argued that the volatile social and political conditions ofGreece were more suitable to the employment of small, professional construction teams than of large bodies of unskilled labour, making the crane preferable to the Greekpolis over the more labour-intensive ramp which had been the norm in the autocratic societies ofEgypt orAssyria.[9]
The first unequivocal literary evidence for the existence of the compound pulley system appears in theMechanical Problems (Mech. 18, 853a32–853b13) attributed toAristotle (384–322 BC), but perhaps composed at a slightly later date. Around the same time, block sizes at Greek temples began to match their archaic predecessors again, indicating that the more sophisticated compound pulley must have found its way to Greek construction sites by then.[10]
Greco-RomanPentaspastos ("Five-pulley-crane"), a medium-sized variant (c. 450 kg load)Reconstruction of a 10.4 m high RomanPolyspastos powered by a treadwheel atBonn, Germany
The heyday of the crane in ancient times came during theRoman Empire, when construction activity soared and buildings reached enormous dimensions. The Romans adopted the Greek crane and developed it further. There is much available information about their lifting techniques, thanks to rather lengthy accounts by the engineersVitruvius (De Architectura 10.2, 1–10) andHeron of Alexandria (Mechanica 3.2–5). There are also two surviving reliefs of Romantreadwheel cranes, with theHaterii tombstone from the late first century AD being particularly detailed.
The simplest Roman crane, thetrispastos, consisted of a double-beam jib, awinch, arope, and a block containing three pulleys. Having thus amechanical advantage of 3:1, it has been calculated that a single man working the winch could raise 150 kg (330 lb) (3 pulleys x 50 kg or 110 lb = 150), assuming that 50 kg (110 lb) represent the maximum effort a man can exert over a longer time period. Heavier crane types featured five pulleys (pentaspastos) or, in case of the largest one, a set of three by five pulleys (Polyspastos) and came with two, three or four masts, depending on the maximum load. Thepolyspastos, when worked by four men at both sides of the winch, could readily lift 3,000 kg (6,600 lb) (3 ropes x 5 pulleys x 4 men x 50 kg or 110 lb = 3,000 kg or 6,600 lb). If the winch was replaced by a treadwheel, the maximum load could be doubled to 6,000 kg (13,000 lb) at only half the crew, since the treadwheel possesses a much bigger mechanical advantage due to its larger diameter. This meant that, in comparison to the construction of theancient Egyptianpyramids, where about 50 men were needed to move a 2.5 ton[which?] stone block up the ramp (50 kg (110 lb) per person), the lifting capability of the Romanpolyspastos proved to be60 times higher (3,000 kg or 6,600 lb per person).[11]
However, numerous extant Roman buildings which feature much heavier stone blocks than those handled by thepolyspastos indicate that the overall lifting capability of the Romans went far beyond that of any single crane. At the temple of Jupiter atBaalbek, for instance, thearchitrave blocks weigh up to 60 tons each, and one cornercornice block even over 100 tons, all of them raised to a height of about 19 m (62.3 ft).[10] InRome, the capital block of Trajan's Column weighs 53.3 tons, which had to be lifted to a height of about 34 m (111.5 ft) (seeconstruction of Trajan's Column).[12]
It is assumed that Roman engineers lifted these extraordinary weights by two measures (see picture below for comparable Renaissance technique): First, as suggested by Heron, a lifting tower was set up, whose four masts were arranged in the shape of a quadrangle with parallel sides, not unlike asiege tower, but with the column in the middle of the structure (Mechanica 3.5).[13] Second, a multitude ofcapstans were placed on the ground around the tower, for, although having a lower leverage ratio than treadwheels, capstans could be set up in higher numbers and run by more men (and, moreover, by draught animals).[14] This use of multiple capstans is also described byAmmianus Marcellinus (17.4.15) in connection with the lifting of theLateranense obelisk in theCircus Maximus (c. 357 AD). The maximum lifting capability of a single capstan can be established by the number of lewis iron holes bored into the monolith. In case of the Baalbek architrave blocks, which weigh between 55 and 60 tons, eight extant holes suggest an allowance of 7.5 ton per lewis iron, that is per capstan.[15] Lifting such heavy weights in a concerted action required a great amount of coordination between the work groups applying the force to the capstans.
Medieval (15th century) port crane for mounting masts and lifting cargo inGdańsk[16]
During theHigh Middle Ages, the treadwheel crane was reintroduced on a large scale after the technology had fallen into disuse in western Europe with the demise of theWestern Roman Empire.[17] The earliest reference to a treadwheel (magna rota) reappears in archival literature in France about 1225,[18] followed by an illuminated depiction in a manuscript of probably also French origin dating to 1240.[19] In navigation, the earliest uses of harbor cranes are documented forUtrecht in 1244,Antwerp in 1263,Bruges in 1288 andHamburg in 1291,[20] while in England the treadwheel is not recorded before 1331.[21]
Generally, vertical transport could be done more safely and inexpensively by cranes than by customary methods. Typical areas of application were harbors, mines, and, in particular, building sites where the treadwheel crane played a pivotal role in the construction of the loftyGothic cathedrals. Nevertheless, both archival and pictorial sources of the time suggest that newly introduced machines like treadwheels orwheelbarrows did not completely replace more labor-intensive methods likeladders,hods andhandbarrows. Rather, old and new machinery continued to coexist on medieval construction sites[22] and harbors.[20]
Apart from treadwheels, medieval depictions also show cranes to be powered manually by windlasses with radiatingspokes,cranks and by the 15th century also by windlasses shaped like aship's wheel. To smooth out irregularities of impulse and get over 'dead-spots' in the lifting processflywheels are known to be in use as early as 1123.[23]
The exact process by which the treadwheel crane was reintroduced is not recorded,[18] 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 thewindlass from which the treadwheel structurally and mechanically evolved. Alternatively, the medieval treadwheel may represent a deliberate reinvention of its Roman counterpart drawn fromVitruvius'De architectura which was available in many monastic libraries. Its reintroduction may have been inspired, as well, by the observation of the labor-saving qualities of thewaterwheel with which early treadwheels shared many structural similarities.[21]
The medieval treadwheel was a large wooden wheel turning around acentral shaft with a treadway 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,[24] giving the possibility of using a thinner shaft and providing thus a greater mechanical advantage.[25]
Single treadwheel crane working from top of the building
Contrary to a popularly held belief, cranes on medieval building sites were neither placed on the extremely lightweightscaffolding 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 tie beams 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.[26] 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.[27]
Less frequently, medieval illuminations also show cranes mounted on the outside of walls with the stand of the machine secured toputlogs.[28]
Tower crane at the inland harbour ofTrier from 1413
In contrast to modern cranes, medieval cranes and hoists — much like their counterparts in Greece and Rome[29] — were primarily capable of a vertical lift, and not used to move loads for a considerable distance horizontally as well.[26] Accordingly, 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,[26] 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.[29] Additionally, the crane master who usually gave orders at the treadwheel workers from outside the crane was able to manipulate the movement laterally by a small rope attached to the load.[30] Slewing cranes which allowed a rotation of the load and were thus particularly suited for dockside work appeared as early as 1340.[31] While ashlar blocks were directly lifted by sling, lewis or devil's clamp (GermanTeufelskralle), other objects were placed before in containers likepallets,baskets, wooden boxes orbarrels.[32]
It is noteworthy that medieval cranes rarely featuredratchets orbrakes to forestall the load from running backward.[33] This curious absence is explained by the highfriction force exercised by medieval tread-wheels which normally prevented the wheel from accelerating beyond control.[30]
A crane constructed in 1742, used for mountingmasts to large sailing vessels. Copenhagen, DenmarkDetail view of a (small) crane in the harbour,V&A Waterfront
According to the "present state of knowledge" unknown in antiquity, stationary harbor cranes are considered a new development of the Middle Ages.[20] The typical harbor crane was a pivoting structure equipped with double treadwheels. These cranes were placed docksides for the loading and unloading of cargo where they replaced or complemented older lifting methods likesee-saws,winches andyards.[20]
Two different types of harbor 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 harbors typically featured tower cranes where the windlass and treadwheels were situated in a solid tower with only jib arm and roof rotating.[16] 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.[34]
Unlike construction cranes where the work speed was determined by the relatively slow progress of the masons, harbor 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.[20] Their capacity was 2–3 tons, which apparently corresponded to the customary size of marine cargo.[20] Today, according to one survey, fifteen treadwheel harbor cranes from pre-industrial times are still extant throughout Europe.[35] Some harbour cranes were specialised at mounting masts to newly built sailing ships, such as inGdańsk,Cologne andBremen.[16] Beside these stationary cranes,floating cranes, which could be flexibly deployed in the whole port basin came into use by the 14th century.[16]
Asheer hulk (or shear hulk) was used in shipbuilding and repair as afloating crane in the days ofsailing ships, primarily to place the lowermasts of a ship under construction or repair. Booms known assheers were attached to the base of a hulk's lower masts or beam, supported from the top of those masts.Blocks and tackle were then used in such tasks as placing or removing the lower masts of the vessel under construction or repair. These lower masts were the largest and most massive single timbers aboard a ship, and erecting them without the assistance of either a sheer hulk or land-basedmasting sheer was extremely difficult.[36]
The concept of sheer hulks originated with the Royal Navy in the 1690s, and persisted in Britain until the early nineteenth century. Most sheer hulks were decommissioned warships;Chatham, built in 1694, was the first of only three purpose-built vessels.[37] There were at least six sheer hulks in service in Britain at any time throughout the 1700s. The concept spread to France in the 1740s with the commissioning of a sheer hulk at the port of Rochefort.[38]
A lifting tower similar to that of the ancient Romans was used to great effect by theRenaissance architectDomenico Fontana in 1586 to relocate the 361 t heavyVatican obelisk in Rome.[39] From his report, it becomes obvious that the coordination of the lift between the various pulling teams required a considerable amount of concentration and discipline, since, if the force was not applied evenly, the excessive stress on the ropes would make them rupture.[40]
Cranes were also used domestically during this period. The chimney or fireplace crane was used to swing pots and kettles over the fire and the height was adjusted by atrammel.[41]
Examples of early modern cranes
Erection of theVatican obelisk in 1586 by means of a lifting tower
An 1868 photo of a 15th-century crane on the unfinished south tower ofCologne Cathedral
With the onset of theIndustrial Revolution the first modern cranes were installed at harbours for loading cargo. In 1838, the industrialist and businessmanWilliam Armstrong designed a water-poweredhydraulic crane. His design used a ram in a closed cylinder that was forced down by a pressurized fluid entering the cylinder and a valve regulated the amount of fluid intake relative to the load on the crane.[42] This mechanism, thehydraulic jigger, then pulled on a chain to lift the load.
In 1845 a scheme was set in motion to provide piped water from distant reservoirs to the households ofNewcastle. Armstrong was involved in this scheme and he proposed to Newcastle Corporation that the excess water pressure in the lower part of town could be used to power one of his hydraulic cranes for the loading of coal onto barges at theQuayside. He claimed that his invention would do the job faster and more cheaply than conventional cranes. The corporation agreed to his suggestion, and the experiment proved so successful that three more hydraulic cranes were installed on the Quayside.[43]
The success of his hydraulic crane led Armstrong to establish theElswick works atNewcastle, to produce hishydraulic machinery for cranes and bridges in 1847. His company soon received orders for hydraulic cranes from Edinburgh and Northern Railways and fromLiverpool Docks, as well as for hydraulic machinery for dock gates inGrimsby. The company expanded from a workforce of 300 and an annual production of 45 cranes in 1850, to almost 4,000 workers producing over 100 cranes per year by the early 1860s.[43]
Armstrong spent the next few decades constantly improving his crane design; his most significant innovation was thehydraulic accumulator. Where water pressure was not available on site for the use of hydraulic cranes, Armstrong often built high water towers to provide a supply of water at pressure. However, when supplying cranes for use atNew Holland on theHumber Estuary, he was unable to do this, because the foundations consisted of sand. He eventually produced the hydraulic accumulator, a cast-iron cylinder fitted with a plunger supporting a very heavy weight. The plunger would slowly be raised, drawing in water, until the downward force of the weight was sufficient to force the water below it into pipes at great pressure. This invention allowed much larger quantities of water to be forced through pipes at a constant pressure, thus increasing the crane's load capacity considerably.[44]
One of his cranes, commissioned by theItalian Navy in 1883 and in use until the mid-1950s, is still standing inVenice, where it is now in a state of disrepair.[45]
Unlike the despotic societies ofEgypt orAssyria, which could mobilize massive unskilledlabor forces usingramps, Greek city-states employed smaller, professional construction teams. This labor constraint necessitatedmechanical advantage provided by thewinch andpulley system, replacing labor-intensive ramps. As a result, Greekarchitecture witnessed a temporary reduction in block weights to accommodate the initial capacity limitations of these machines (15 to 20metric tons), before the development ofcompound pulley systems enabled the movement of heavier loads.[48]
Roman relief from the Tomb of the Haterii showing a construction crane with a pulley system
Roman engineers advanced Greek designs by analyzing mechanical advantage ratios. The simplest Roman crane, thetrispastos, consisted of a single-beamjib and ablock with threepulleys, creating a 3:1 mechanical advantage. Assuming a single worker could apply 50 kg offorce, this system enabled lifting 150 kg. For managing heavier loads, Romans developed thepentaspastos (five pulleys) and thepolyspastos (three sets of five pulleys).[49]
The polyspastos represented a major leap in mechanical efficiency. When powered by four men operating a winch, it could lift 3,000 kg. However, substituting the winch with atreadwheel—a large wooden wheel rotated by men walking inside it—doubled this capacity to 6,000 kg with half the crew. This efficiency increase resulted from the treadwheel's largerdiameter creating a much greatermoment arm compared to a hand winch. This system increased lifting efficiency by 60 times compared toEgyptian pyramid construction, where approximately 50 men were required to move a 2.5-tonne stone block up a ramp.[50]
Roman crane mechanical advantage
Crane type
Pulleys
Power source
Capacity (kg)
Trispastos
3
1 worker (winch)
150
Pentaspastos
5
—
250
Polyspastos
15 (3×5)
4 workers (winch)
3,000
Polyspastos
15 (3×5)
2 workers (treadwheel)
6,000
For loads exceeding single-crane capacity, such as thearchitrave blocks of theTemple of Jupiter atBaalbek weighing up to 60tons, Roman engineers employed lifting towers and arrays ofcapstans coordinated by large numbers of workers oranimals.[51]
During the medieval period, Persian engineers advanced lifting technology significantly, bridging the gap between ancient mechanics and modern engineering.Al-Jazari (1136–1206), working in theArtuqid court, documented revolutionarylifting mechanisms including early versions of thecrankshaft,camshaft, andreciprocating pump in hisBook of Knowledge of Ingenious Mechanical Devices (1206 CE). These innovations transformed water-lifting from manual systems to semi-automated mechanisms. Notable applications included theDamascus hydraulic systems, wheresaqiya chain pumps powered byhydropower supplied water to major institutions for centuries, introducing mechanical principles like the conversion of rotary motion to reciprocating motion that later became central to modern crane winches.[52]
TheGdańsk crane, a medievaltreadwheel crane built in 1442–1444, one of the largest and best-preserved harbor cranes from the Middle Ages
In the latemedieval period in Europe,treadwheel cranes reappeared after a period of disuse following thefall of the Western Roman Empire. This technological resurgence coincided with the emergence ofGothic architecture and the need to construct tallcathedrals. Contrary to common belief, medieval cranes were not positioned on lightscaffolding but were initially placed on the ground and, as construction progressed, mounted onroof beams and transferred from onebay to another—a process that allowed the crane to "grow" and "wander" with the building.[53]
Interior of a medieval treadwheel crane inBruges, Belgium, showing the wooden wheel mechanism powered by human walking
The development of fixedharbor cranes during the medieval period represented a true innovation unknown in antiquity. These cranes, designed for rapidloading and unloading ofships, typically featured double treadwheels to increase operational speed. Various types developed, includinggantry cranes with vertical pivot axes on the shores ofFlanders and theNetherlands, andtower cranes in Germanports embedded in sturdy stone towers.[54]
For stability, the sum of allmoments about the base of the crane must be close to zero so that the crane does not overturn.[58] The principle ofmoment equilibrium (ΣM = 0) is fundamental to crane design, where M represents moments about the crane'scenter of rotation. In practice, the magnitude of load that is permitted to be lifted (called the "rated load" in theUnited States) is some value less than the load that will cause the crane to tip, thus providing asafety margin.
European standards (EN 13000:2010) adopt similar principles but with differentsafety factors reflecting different regulatory philosophies regardingrisk tolerance.[61] For mobile cranes onoutriggers, the rated capacity under European standards is typically 80% of the tipping load, whilecrawler cranes are rated at 70% of the tipping load.[61]
Safety margins typically range between 10-25% above a crane's rated capacity. However, regular operation near or above rated capacity significantly increaseswear on components, resulting in highermaintenance costs and shortened operational lifespan. The design must account forfatigue cycles, with typical design life of 20 years or 2 million load cycles perISO 12482-1:2014.[62]
Formobile cranes onoutriggers, stability depends critically onground conditions. The typical outrigger pad exertspressures of 50-200kPa (7-29psi).Engineering guidelines requiresoilbearing capacity assessments before crane setup, with mandatory use of timber mats or engineeredcribbing when soil capacity is below 150 kPa. Inadequate ground preparation is a leading cause of crane tipping accidents, particularly inconstruction sites with variablesoil conditions.[63]
Standards for cranes mounted onships oroffshore platforms are somewhat stricter because of the dynamic load on the crane due tovessel motion.[64] For loads not associated with manned operations, allowable loads must factor in dynamicaccelerations including 1.75g vertical, 0.75 g longitudinal, and 0.75 g transverse acceleration, meaning a 2000 kg static load requires crane capacity for 3500 kg at sea. Additionally, the stability of the vessel or platform must be considered.[65]
For stationary pedestal or kingpost mounted cranes, themoment produced by the boom, jib, and load is resisted by the pedestal base or kingpost.Stress within the base must be less than theyield stress of the material or the crane will fail.[66] The design must account forfatigue loading, wind-inducedoscillations, andthermal expansion effects over the crane's operational lifetime.
The dynamic lift factor (DLF), also known as the design dynamic factor, is a critical parameter in crane design and operation. It accounts for the dynamic effects that can increase the load on a crane's structure and components during lifting operations.[67][68] These effects include hoistingacceleration and deceleration of the load, crane movement such asslewing orluffing, swinging of suspended loads,wind forces acting on the crane, the load and the rigging, and operator error or other unexpected events.[69][70]
The DLF for a new crane design can be determined with analytical calculations and mathematical models following the relevant designspecifications. More sophisticated methods, such asfinite element analysis or other simulation techniques, may also be used to model the crane's behavior under various loading conditions, as deemed appropriate by the designer or certifying authority. To verify the actual DLF, control load tests can be conducted on the completed crane using instrumentation such asload cells,accelerometers, andstrain gauges. This process is usually part of the crane'stype approval.[67]
Jib cranes typically have a lower DLF () compared to travelinggantry cranes () because they are stiffer.[71] Forgrab bucket cranes, the DLF can increase by 20% to 30% reflecting theshock loads caused by the release of the lifted material.[67] The DLF generally decreases as themass of the lifted object increases, as cranes tend to operate at lowervelocities with heavier loads to ensure safety and stability.
In offshore lifting, where the crane and/or lifted object are on afloatingvessel, the DLF is higher compared to onshore lifts because of the additional movement caused bywave action.[67][64]Wave-induced vessel motions includingheave,pitch, androll are translated down the lifting wire, resulting in submerged loads beingaccelerated in response to forces induced by ship motions, with peaktension equal toweight plusinertial effects plusdrag effects. The DLF further increases when lifting objects underwater or through thesplash zone.[72] For offshore lifts, the DLF typically decreases from 1.3 at 100tonnes to 1.1 at 2500 tonnes as heavier loads require slower, more controlled operations.[73]
Designwind speeds per American Society of Civil Engineers (ASCE) 7-16 andISO 4302:2016 are 20m/s (72km/h) for in-service conditions and 42 m/s (150 km/h) for out-of-service survival.[74] Thewind force on a load can be calculated as where is thedrag coefficient (typically 1.0-2.0 depending on load shape), is the projectedarea in m², and is wind speed in m/s.[74]
The working load is the totalweight that a crane is designed to safely lift under normal operating conditions:[67]
where is the working load, is theacceleration of gravity (9.81 m/s²), is the maximum liftedmass (working load limit or safe working load), and is the mass of lifting appliances or parts of the crane that move with the lifted mass.
The DLF is then used as amultiplier to determine theforce applied to the crane structure and components:[67]
where is relativevelocity between lifted object and lifting equipment at the time of pick-up, and is thestiffness of the cranesystem at the lifting point. The relative velocity is dependent on the crane's operational requirements and the system stiffness can be determined bycalculation orloaddeflectiontests.[67]
The most basictruck-mounted crane configuration is a "boom truck" or "lorry loader", which features a rear-mounted rotating telescopic-boom crane mounted on a commercial truck chassis.[78][79]
Larger, heavier duty, purpose-built "truck-mounted" cranes are constructed in two parts: the carrier, often called thelower, and the lifting component, which includes the boom, called theupper. These are mated together through a turntable, allowing the upper to swing from side to side. These modern hydraulic truck cranes are usually single-engine machines, with the same engine powering the undercarriage and the crane. The upper is usually powered via hydraulics run through the turntable from the pump mounted on the lower. In older model designs of hydraulic truck cranes, there were two engines. One in the lower pulled the crane down the road and ran a hydraulic pump for the outriggers and jacks. The one in the upper ran the upper through a hydraulic pump of its own. Many older operators favor the two-engine system due to leaking seals in the turntable of aging newer design cranes. Hiab invented the world's first hydraulic truck mounted crane in 1947.[80] The name, Hiab, comes from the commonly used abbreviation of Hydrauliska Industri AB, a company founded in Hudiksvall, Sweden 1944 by Eric Sundin, a ski manufacturer who saw a way to utilize a truck's engine to power loader cranes through the use of hydraulics.
Generally, these cranes are able to travel on highways, eliminating the need for special equipment to transport the crane unless weight or other size constrictions are in place such as local laws. If this is the case, most larger cranes are equipped with either special trailers to help spread the load over more axles or are able to disassemble to meet requirements. An example is counterweights. Often a crane will be followed by another truck hauling the counterweights that are removed for travel. In addition some cranes are able to remove the entire upper. However, this is usually only an issue in a large crane and mostly done with a conventional crane such as a Link-Belt HC-238. When working on the job site,outriggers are extended horizontally from the chassis then vertically to level and stabilize the crane while stationary andhoisting. Many truck cranes have slow-travelling capability (a few miles per hour) while suspending a load. Great care must be taken not to swing the load sideways from the direction of travel, as most anti-tipping stability then lies in the stiffness of the chassis suspension. Most cranes of this type also have moving counterweights for stabilization beyond that provided by the outriggers. Loads suspended directly aft are the most stable, since most of the weight of the crane acts as a counterweight. Factory-calculated charts (orelectronic safeguards) are used by crane operators to determine the maximum safe loads for stationary (outriggered) work as well as (on-rubber) loads and travelling speeds.
Truck cranes range in lifting capacity from about 14.5short tons (12.9long tons; 13.2 t) to about 2,240 short tons (2,000 long tons; 2,032 t).[81][82] Although most only rotate about 180 degrees, the more expensive truck mounted cranes can turn a full 360 degrees.
Examples of truck mounted cranes
Automobile crane of the Railway Troops of Russia
Truck mounted crane building a bridge
A truck-mounted crane in road travel configuration
A loader crane (also called aknuckle-boom crane orarticulating crane) is a hydraulically powered articulated arm fitted to atruck ortrailer, and is used for loading/unloading the vehicle cargo. The numerous jointed sections can be folded into a small space when the crane is not in use. One or more of the sections may betelescopic. Often the crane will have a degree of automation and be able to unload or stow itself without an operator's instruction.
Unlike most cranes, the operator must move around the vehicle to be able to view his load; hence modern cranes may be fitted with a portable cabled or radio-linked control system to supplement the crane-mounted hydraulic control levers.
In the United Kingdom and Canada, this type of crane is often known colloquially as a "Hiab", partly because this manufacturer invented the loader crane and was first into the UK market, and partly because the distinctive name was displayed prominently on the boom arm.[83]
Arolloader crane is a loader crane mounted on a chassis with wheels. This chassis can ride on the trailer. Because the crane can move on the trailer, it can be a light crane, so the trailer is allowed to transport more goods.
A telescopic crane has a boom that consists of a number of tubes fitted one inside the other. Ahydraulic cylinder or other powered mechanism extends or retracts the tubes to increase or decrease the total length of the boom. These types of booms are often used for short term construction projects, rescue jobs, lifting boats in and out of the water, etc. The relative compactness of telescopic booms makes them adaptable for many mobile applications.
Though not all telescopic cranes are mobile cranes, many of them are truck-mounted.
A telescopic tower crane has a telescopic mast and often a superstructure (jib) on top so that it functions as a tower crane. Some telescopic tower cranes also have a telescopic jib.
A rough terrain crane has aboom mounted on anundercarriage atop four rubber tires that is designed foroff-road pick-and-carry operations. Outriggers are used to level and stabilize the crane for hoisting.[84]
These telescopic cranes are single-engine machines, with the same engine powering the undercarriage and the crane, similar to a crawler crane. The engine is usually mounted in the undercarriage rather than in the upper, as with crawler crane. Most have 4 wheel drive and 4 wheel steering for traversing tighter and slicker terrain than a standard truck crane, with less site prep.
An all-terrain crane is a hybrid combining the roadability of a truck-mounted and on-site maneuverability of a rough-terrain crane. It can both travel at speed on public roads and maneuver on rough terrain at the job site using all-wheel and crab steering.
A crawler crane has its boom mounted on an undercarriage fitted with a set ofcrawler tracks that provide both stability and mobility. Crawler cranes range in lifting capacity from about 40 to 4,000 long tons (44.8 to 4,480.0 short tons; 40.6 to 4,064.2 t) as seen from theXGC88000 crawler crane.[86]
The main advantage of a crawler crane is its ready mobility and use, since the crane is able to operate on sites with minimal improvement and stable on its tracks without outriggers. Wide tracks spread the weight out over a great area and are far better than wheels at traversing soft ground without sinking in. A crawler crane is also capable of traveling with a load. Its main disadvantage is its weight, making it difficult and expensive to transport. Typically a large crawler must be disassembled at least into boom and cab and moved by trucks, rail cars or ships to its next location.[87]
A pick and carry crane is similar to a mobile crane in that is designed to travel on public roads; however, pick and carry cranes have no stabiliser legs or outriggers and are designed to lift the load and carry it to its destination, within a small radius, then be able to drive to the next job. Pick and carry cranes are popular in Australia, where large distances are encountered between job sites. One popular manufacturer in Australia was Franna, who have since been bought by Terex, and now all pick and carry cranes are commonly called "Frannas", even though they may be made by other manufacturers. Nearly every medium- and large-sized crane company in Australia has at least one and many companies have fleets of these cranes. The capacity range is between 10 and 40 t (9.8 and 39.4 long tons; 11 and 44 short tons) as a maximum lift, although this is much less as the load gets further from the front of the crane. Pick and carry cranes have displaced the work usually completed by smaller truck cranes, as the set-up time is much quicker. Many steel fabrication yards also use pick and carry cranes, as they can "walk" with fabricated steel sections and place these where required with relative ease.
Smaller pick and carry cranes may be based on an articulated tractor chassis, with the boom mounted over the front wheels. In Australia these are popularly known as "wobbly cranes".[88]
A carry deck crane is a small 4 wheel crane with a 360-degree rotating boom placed right in the centre and an operators cab located at one end under this boom. The rear section houses the engine and the area above the wheels is a flat deck. Very much an American invention the Carry deck can hoist a load in a confined space and then load it on the deck space around the cab or engine and subsequently move to another site. The Carry Deck principle is the American version of the pick and carry crane and both allow the load to be moved by the crane over short distances.
Telescopic handlers areforklift-like trucks that have a set of forks mounted on a telescoping extendable boom like a crane. Early telescopic handlers only lifted in one direction and did not rotate;[89] however, several of the manufacturers have designed telescopic handlers that rotate 360 degrees through a turntable and these machines look almost identical to the Rough Terrain Crane. These new 360-degree telescopic handler/crane models have outriggers or stabiliser legs that must be lowered before lifting; however, their design has been simplified so that they can be more quickly deployed. These machines are often used to handle pallets of bricks and install frame trusses on many new building sites and they have eroded much of the work for small telescopic truck cranes. Many of the world's armed forces have purchased telescopic handlers and some of these are the much more expensive fully rotating types. Their off-road capability and their on site versatility to unload pallets using forks, or lift like a crane make them a valuable piece of machinery.
Tower cranes are a modern form of balance crane that consist of the same basic parts. Fixed to the ground on a concrete slab (and sometimes attached to the sides of structures), tower cranes often give the best combination of height and lifting capacity and are used in the construction of tall buildings. The base is then attached to the mast which gives the crane its height. Further, the mast is attached to the slewing unit (gear and motor) that allows the crane to rotate. On top of the slewing unit there are three main parts which are: the long horizontal jib (working arm), shorter counter-jib, and the operator's cab.
Optimization of tower crane location in the construction sites has an important effect on material transportation costs of a project,[92] but site operators need to ensure they assess where the jib will oversail the property of other landowners and tenants as it rotates over the site. UnderEnglish law a landowner also owns the airspace above their property and developers will need to agree terms with adjacent property owners before oversailing their land.[93]
The long horizontal jib is the part of the crane that carries the load. The counter-jib carries a counterweight, usually of concrete blocks, while the jib suspends the load to and from the center of the crane. The crane operator either sits in a cab at the top of the tower or controls the crane by radio remote control from the ground. In the first case the operator's cab 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 the crane operator using electric motors to manipulate wire rope cables through a system of sheaves. The hook is located on the long horizontal arm to lift the load which also contains its motor.
In order to hook and unhook the loads, the operator usually works in conjunction with a signaller (known as a "dogger", "rigger" or "swamper"). They are most often in radio contact, and always use hand signals. The rigger or dogger directs the schedule of lifts for the crane, and is responsible for the safety of therigging and loads.
Tower cranes can achieve a height under hook of over 100 metres.[94]
Tower cranes are used extensively in construction and other industry to hoist and move materials. There are many types of tower cranes. Although they are different in type, the main parts are the same, as follows:
Mast: the main supporting tower of the crane. It is made of steel trussed sections that are connected together during installation.
Slewing unit: the slewing unit sits at the top of the mast. This is the engine that enables the crane to rotate.
Operating cabin: on most tower cranes the operating cabin sits just above the slewing unit. It contains the operating controls, load-movement indicator system (LMI), scale, anemometer, etc.
Jib: the jib, or operating arm, extends horizontally from the crane. A "luffing" jib is able to move up and down; a fixed jib has a rolling trolley car that runs along the underside to move loads horizontally.
Counter jib: holds counterweights, hoist motor, hoist drum and the electronics. (In many older tower crane designs the hoisting devices and electronics were located in the mast foot.)[95]
Hoist winch: the hoist winch assembly consists of the hoist winch (motor, gearbox, hoist drum, hoist rope, and brakes), the hoist motor controller, and supporting components, such as the platform. Many tower cranes have transmissions with two or more speeds.
Hook: the hook is used to connect the material to the crane, suspended from the hoist rope either at the tip (on luffing jib cranes) or routed through the trolley (on hammerhead cranes).
Weights: Large, moveable concrete counterweights are mounted toward the rear of the counterdeck, to compensate for the weight of the goods lifted and keep the center of gravity over the supporting tower.[96]
A tower crane is usually assembled by a telescopic jib (mobile) crane of greater reach (also see "self-erecting crane" below) and in the case of tower cranes that have risen while constructing very tall skyscrapers, a smaller crane (orderrick) will often be lifted to the roof of the completed tower to dismantle the tower crane afterwards, which may be more difficult than the installation.[97]
Tower cranes can be operated by remote control, removing the need for the crane operator to sit in a cab atop the crane.
Each model and distinctive style of tower crane has a predetermined lifting chart that can be applied to any radii available, depending on its configuration. Similar to a mobile crane, a tower crane may lift an object of far greater mass closer to its center of rotation than at its maximum radius. An operator manipulates several levers and pedals to control each function of the crane.
When a tower crane is used in proximity to buildings, roads, power lines, or other tower cranes, atower crane anti-collision system is used. This operator support system reduces the risk of a dangerous interaction occurring between a tower crane and another structure.
In some countries, such as France, tower crane anti-collision systems are mandatory.[98]
A self-erecting tower crane folds and unfolds itself
Generally a type of pedestrian operated tower crane, self-erecting tower cranes are transported as a single unit and can be assembled by a qualified technician without the assistance of a larger mobile crane. They are bottom slewing cranes that stand on outriggers, have no counter jib, have their counterweights and ballast at the base of the mast, cannot climb themselves, have a reduced capacity compared to standard tower cranes, and seldom have an operator's cabin.
In some cases, smaller self-erecting tower cranes may have axles permanently fitted to the tower section to make maneuvering the crane onsite easier.
Tower cranes can also use a hydraulic-powered jack frame to raise themselves to add new tower sections without any additional other cranes assisting beyond the initial assembly stage. This is how it can grow to nearly any height needed to build the tallest skyscrapers when tied to a building as the building rises. The maximum unsupported height of a tower crane is around 265 ft.[99] For a video of a crane getting taller, see "Crane Building Itself" on YouTube.[100]
For another animation of such a crane in use, see "SAS Tower Construction Simulation" on YouTube.[101] Here, the crane is used to erect a scaffold, which, in turn, contains a gantry to lift sections of a bridge spire.
Many tower cranes are designed to "jump" in stages, effectively lifting themselves to the next level. A specialty example of a climbing crane was introduced by Lagerwey Wind andEnercon[This paragraph needs citation(s)] to construct awind turbine tower, where instead of erecting a large crane a smaller climbing crane can raise itself with the structure's construction, lift the generator housing to its top, add the rotor blades, then climb down.
A reach stacker is a vehicle used for handlingintermodal cargo containers in small terminals or medium-sized ports. Reach stackers are able to transport a container short distances very quickly and pile them in various rows depending on its access.
Asidelifter crane is a road-goingtruck orsemi-trailer, able to hoist and transport ISO standardcontainers. Container lift is done with parallel crane-like hoists, which can lift a container from the ground or from arailway vehicle.
Atravel lift (also called a boat gantry crane, or boat crane) is a crane with two rectangular side panels joined by a single spanning beam at the top of one end. The crane is mobile with four groups of steerable wheels, one on each corner. These cranes allow boats with masts or tall super structures to be removed from the water and transported around docks or marinas.[102] Not to be confused mechanical device used for transferring a vessel between two levels of water, which is also called aboat lift.
Ring cranes are some of the largest and heaviest land-based cranes ever designed. A ring-shaped track support the main superstructure allowing for extremely heavy loads (up to thousands of tonnes).
The "hammerhead", or giantcantilever, crane is a fixed-jib crane consisting of a steel-braced tower on which revolves a large, horizontal, doublecantilever; the forward part of this cantilever orjib carries the lifting trolley, the jib is extended backwards in order to form a support for the machinery and counterbalancing weight. In addition to the motions of lifting and revolving, there is provided a so-called "racking" motion, by which the lifting trolley, with the load suspended, can be moved in and out along the jib without altering the level of the load. Such horizontal movement of the load is a marked feature of later crane design.[103] These cranes are generally constructed in large sizes and can lift up to 350 tons.[104]
The design ofHammerkran evolved first in Germany around the turn of the 19th century and was adopted and developed for use inBritishshipyards to support the battleship construction program from 1904 to 1914. The ability of the hammerhead crane to lift heavy weights was useful for installing large pieces ofbattleships such asarmour plate andgun barrels. Giant cantilever cranes were also installed in naval shipyards inJapan and in theUnited States. The British government also installed a giant cantilever crane at theSingapore Naval Base (1938) and later a copy of the crane was installed atGarden Island Naval Dockyard inSydney (1951). These cranes provided repair support for the battle fleet operating far fromGreat Britain.
In the British Empire, the engineering firmSir William Arrol & Co. was the principal manufacturer of giant cantilever cranes; the company built a total of fourteen. Among the sixty built in the world, few remain; seven in England and Scotland of about fifteen worldwide.[105]
Normally a crane with a hinged jib will tend to have its hook also move up and down as the jib moves (orluffs). Alevel luffing crane is a crane of this common design, but with an extra mechanism to keep the hook at the same level when the jib is pivoted in or out.
Anoverhead crane being used in typical machine shop. Thehoist is operated via a wired pushbutton station to move system and the load in any direction.
Anoverhead crane, also known as a bridge crane, is a type of crane where the hook-and-line mechanism runs along a horizontal beam that itself runs along two widely separated rails. Often it is in a long factory building and runs along rails along the building's two long walls. It is similar to agantry crane. Overhead cranes typically consist of either a single beam or a double beam construction. These can be built using typical steel beams or a more complex box girder type. Pictured on the right is a single bridge box girder crane with thehoist and system operated with a control pendant. Double girder bridge are more typical when needing heavier capacity systems from 10 tons[which?] and above. The advantage of the box girder type configuration results in a system that has a lower deadweight yet a stronger overall system integrity. Also included would be a hoist to lift the items, the bridge, which spans the area covered by the crane, and a trolley to move along the bridge.
The most common overhead crane use is in thesteel industry. At every step of the manufacturing process, until it leaves a factory as a finished product,steel is handled by an overhead crane. Raw materials are poured into afurnace by crane, hot steel is stored for cooling by an overhead crane, the finished coils are lifted and loaded ontotrucks andtrains by overhead crane, and thefabricator or stamper uses an overhead crane to handle the steel in his factory. Theautomobile industry uses overhead cranes for handling of raw materials. Smallerworkstation cranes handle lighter loads in a work-area, such asCNC mill or saw.
Almost all paper mills use bridge cranes for regular maintenance requiring removal of heavy press rolls and other equipment. The bridge cranes are used in the initial construction of paper machines because they facilitate installation of the heavy cast iron paper drying drums and other massive equipment, some weighing as much as 70 tons.
In many instances the cost of a bridge crane can be largely offset with savings from not renting mobile cranes in the construction of a facility that uses a lot of heavy process equipment.
Thiselectric overhead traveling crane is most common type of overhead crane, found in many factories. These cranes are electrically operated by a control pendant, radio/IR remote pendant, or from an operator cabin attached to the crane.
A gantry crane has ahoist in a fixed machinery house or on a trolley that runs horizontally along rails, usually fitted on a single beam (mono-girder) or two beams (twin-girder). The crane frame is supported on a gantry system with equalized beams and wheels that run on the gantry rail, usually perpendicular to the trolley travel direction. These cranes come in all sizes, and some can move very heavy loads, particularly the extremely large examples used in shipyards or industrial installations. A special version is thecontainer crane (or "Portainer" crane, named by the first manufacturer), designed for loading and unloading ship-borne containers at a port.
A jib crane is a type of crane - not to be confused with a crane rigged with a jib to extend its main boom - where a horizontal member (jib orboom), supporting a moveable hoist, is fixed to a wall or to a floor-mounted pillar. Jib cranes are used in industrial premises and on military vehicles. The jib may swing through an arc, to give additional lateral movement, or be fixed. Similar cranes, often known simply as hoists, were fitted on the top floor of warehouse buildings to enable goods to be lifted to all floors.
Bulk-handling cranes are designed from the outset to carry a shell grab or bucket, rather than using a hook and a sling. They are used for bulk cargoes, such as coal, minerals, scrap metal etc.
A crane with a forklift type mechanism used in automated (computer-controlled)warehouses (known as anautomated storage and retrieval system (AS/RS)). The crane moves on a track in an aisle of the warehouse. The fork can be raised or lowered to any of the levels of a storage rack and can be extended into the rack to store and retrieve the product. The product can in some cases be as large as anautomobile. Stacker cranes are often used in the large freezer warehouses of frozen food manufacturers. This automation avoids requiring forklift drivers to work in below-freezing temperatures every day.
Floating cranes are used mainly inbridge building andport construction, but they are also used for occasional loading and unloading of especially heavy or awkward loads on and off ships. Some floating cranes are mounted onpontoons, others are specialized cranebarges with a lifting capacity exceeding 10,000short tons (8,929long tons; 9,072 t) and have been used to transport entire bridge sections. Floating cranes have also been used to salvage sunkenships.
Deck cranes, also known as shipboard or cargo cranes,[107] are located on ships and boats, used for cargo operations where no shore unloading facilities are available, raising and lowering loads (such as shellfish dredges and fish nets) into the water, and small boat unloading and retrieval. Most are diesel-hydraulic or electric-hydraulic, supporting an increasingly automated control interface.[108]
A railroad crane has flanged wheels for use on railroads.The simplest form is a crane mounted on aflatcar. More capable devices are purpose-built. Different types of crane are used formaintenance work, recovery operations and freight loading in goods yards and scrap handling facilities.
Aerial cranes or "sky cranes" usually arehelicopters designed to lift large loads. Helicopters are able to travel to and lift in areas that are difficult to reach by conventional cranes. Helicopter cranes are most commonly used to lift loads onto shopping centers and high-rise buildings. They can lift anything within their lifting capacity, such as air conditioning units, cars, boats, swimming pools, etc. They also perform disaster relief after natural disasters for clean-up, and during wild-fires they are able to carry huge buckets of water to extinguish fires.
Some aerial cranes, mostly concepts, have also used lighter-than air aircraft, such asairships.
Lifetime of existing cranes made of welded metal structures can often be extended for many years by after treatment of welds. During development of cranes, load level (lifting load) can be significantly increased by taking into account the IIW recommendations, leading in most cases to an increase of the permissible lifting load and thus to an efficiency increase.[109]
The generally accepted definition of a crane is a machine for lifting and moving heavy objects by means of ropes or cables suspended from a movable arm. As such, a lifting machine that does not use cables, or else provides only vertical and not horizontal movement, cannot strictly be called a 'crane'.
Goliath is 96 m (315 ft) tall,Samson is 106 m (348 ft)
span 140 m (459 ft), lift-height 70 m (230 ft), capacity 840 tonnes (830 long tons; 930 short tons) each, 1,600 tonnes (1,600 long tons; 1,800 short tons) combined
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