A crane is a machine used to move materials both vertically and horizontally, utilizing a system of a boom, hoist, wire ropes or chains, and sheaves for lifting and relocating heavy objects within the swing of its boom. The device uses one or more simple machines, such as the lever and pulley, to create mechanical advantage to do its work. Cranes are commonly employed in transportation for the loading and unloading of freight, in construction for the movement of materials, and in manufacturing for the assembling of heavy equipment.
The first known crane machine was the shaduf, a water-lifting device that was invented in ancient Mesopotamia (modern Iraq) and then appeared in ancient Egyptian technology. Construction cranes later appeared in ancient 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 the Roman Empire, employing the use of human treadwheels, permitting the lifting of heavier weights. In the High 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, but cast iron, iron and steel took over with the coming of the Industrial Revolution.
For many centuries, power was supplied by the physical exertion of men or animals, although hoists in watermills and windmills could be driven by the harnessed natural power. The first mechanical power was provided by steam engines, the earliest steam crane being introduced in the 18th or 19th century, with many remaining in use well into the late 20th century. Modern cranes usually use internal combustion engines or electric motors and hydraulic 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 build oil rigs and salvage sunken ships.
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.
Contents
Etymology
Cranes were so called from the resemblance to the long neck of the bird, cf. Ancient Greek: γερανός, French grue.
History
Ancient civilizations
The earliest known lifting device was the shadoof, a crane-like device used in Mesopotamia around 3000 BCE, which had a lever mechanism and was used for irrigation purposes. It was invented in Mesopotamia (modern Iraq) circa 3000 BC. The shadouf subsequently appeared in ancient Egyptian technology circa 2000 BC. However, the transition to building cranes occurred in ancient Greece during the late 6th century BCE. Archaeological evidence, including distinctive cuttings for lifting tongs and Lewis irons on stone blocks of Greek temples, indicates a fundamental shift in engineering strategy coinciding with the development of the Greek city-state (polis). 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.
This labor constraint necessitated mechanical advantage provided by the winch and pulley system, replacing labor-intensive ramps. In contrast to the archaic period with its pattern of ever-increasing block sizes, Greek temples of the classical age like the Parthenon 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.
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 of Greece were more suitable to the employment of small, professional construction teams than of large bodies of unskilled labour, making the crane preferable to the Greek polis over the more labour-intensive ramp which had been the norm in the autocratic societies of Egypt or Assyria.
The first unequivocal literary evidence for the existence of the compound pulley system appears in the Mechanical Problems (Mech. 18, 853a32–853b13) attributed to Aristotle (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.
Roman Empire
The heyday of the crane in ancient times came during the Roman 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 engineers Vitruvius and Heron of Alexandria. There are also two surviving reliefs of Roman treadwheel cranes, with the Haterii tombstone from the late first century AD being particularly detailed.
Roman engineers advanced Greek designs by analyzing mechanical advantage ratios. The simplest Roman crane, the trispastos, consisted of a double-beam jib, a winch, a rope, and a block containing three pulleys. Having thus a mechanical 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.
The polyspastos represented a major leap in mechanical efficiency. When worked by four men at both sides of the winch, it 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 the ancient Egyptian pyramids, where about 50 men were needed to move a 2.5 ton stone block up the ramp (50 kg (110 lb) per person), the lifting capability of the Roman polyspastos proved to be 60 times higher (3,000 kg or 6,600 lb per person).
However, substituting the winch with a treadwheel—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 larger diameter creating a much greater moment arm compared to a hand winch. This system increased lifting efficiency by 60 times compared to Egyptian pyramid construction, where approximately 50 men were required to move a 2.5-tonne stone block up a ramp.
However, numerous extant Roman buildings which feature much heavier stone blocks than those handled by the polyspastos indicate that the overall lifting capability of the Romans went far beyond that of any single crane. At the temple of Jupiter at Baalbek, for instance, the architrave blocks weigh up to 60 tons each, and one corner cornice block even over 100 tons, all of them raised to a height of about 19 m (62.3 ft). In Rome, 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) (see construction of Trajan's Column).
Middle Ages
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 the Artuqid court, documented revolutionary lifting mechanisms including early versions of the crankshaft, camshaft, and reciprocating pump in his Book of Knowledge of Ingenious Mechanical Devices (1206 CE). These innovations transformed water-lifting from manual systems to semi-automated mechanisms. Notable applications included the Damascus hydraulic systems, where saqiya chain pumps powered by hydropower 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.
During the High 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 the Western Roman Empire. The earliest reference to a treadwheel (magna rota) reappears in archival literature in France about 1225, followed by an illuminated depiction in a manuscript of probably also French origin dating to 1240. In navigation, the earliest uses of harbor cranes are documented for Utrecht in 1244, Antwerp in 1263, Bruges in 1288 and Hamburg in 1291, while in England the treadwheel is not recorded before 1331.
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 lofty Gothic cathedrals.
Nevertheless, both archival and pictorial sources of the time suggest that newly introduced machines like treadwheels or wheelbarrows did not completely replace more labor-intensive methods like ladders, hods and handbarrows. Rather, old and new machinery continued to coexist on medieval construction sites and harbors.
Apart from treadwheels, 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.
Early modern age
A lifting tower similar to that of the ancient Romans was used to great effect by the Renaissance architect Domenico Fontana in 1586 to relocate the 361 t heavy Vatican obelisk in Rome. 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.
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 a trammel.
Industrial revolution
With the onset of the Industrial Revolution the first modern cranes were installed at harbours for loading cargo. In 1838, the industrialist and businessman William Armstrong designed a water-powered hydraulic 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. This mechanism, the hydraulic 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 of Newcastle. 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 the Quayside. 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.
The success of his hydraulic crane led Armstrong to establish the Elswick works at Newcastle, to produce his hydraulic machinery for cranes and bridges in 1847. His company soon received orders for hydraulic cranes from Edinburgh and Northern Railways and from Liverpool Docks, as well as for hydraulic machinery for dock gates in Grimsby. 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.
Armstrong spent the next few decades constantly improving his crane design; his most significant innovation was the hydraulic 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 at New Holland on the Humber 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.
Mechanical principles
Crane design requires balancing three fundamental considerations: adequate load capacity, stability against tipping, and structural failure prevention. Stability is achieved through moment equilibrium, where permitted loads are significantly less than tipping loads—typically 75-85% in the US and 70-80% in Europe. Ground conditions critically affect stability, with outrigger pads exerting 50-200 kPa pressure. The dynamic lift factor (DLF) accounts for transient forces from hoisting acceleration, crane motion, wave-induced vessel motions in offshore applications, and wind effects (20 m/s in-service, 42 m/s out-of-service). Human factors and modern electronic control systems significantly influence dynamic loading. International standards including ASME B30.5 and EN 13000 establish safety requirements, while sophisticated instrumentation such as load cells, accelerometers, and strain gauges validate crane performance during type approval testing.
Stability
For stability, the sum of all moments about the base of the crane must be close to zero so that the crane does not overturn. The principle of moment equilibrium (ΣM = 0) is fundamental to crane design, where M represents moments about the crane's center of rotation. In practice, the magnitude of load that is permitted to be lifted (called the "rated load" in the United States) is some value less than the load that will cause the crane to tip, thus providing a safety margin.
Under United States standards for mobile cranes, the stability-limited rated load for a crawler crane is 75% of the tipping load, and for outrigger-supported cranes is 85% of the tipping load. These requirements are established by the American Society of Mechanical Engineers in the volume ASME B30.5-2018 Mobile and Locomotive Cranes.
European standards (EN 13000:2010) adopt similar principles but with different safety factors reflecting different regulatory philosophies regarding risk tolerance. For mobile cranes on outriggers, the rated capacity under European standards is typically 80% of the tipping load, while crawler cranes are rated at 70% of the tipping load.
Safety margins typically range between 10 and 25% above a crane's rated capacity. However, regular operation near or above rated capacity significantly increases wear on components, resulting in higher maintenance costs and shortened operational lifespan. The design must account for fatigue cycles, with typical design life of 20 years or 2 million load cycles per ISO 12482-1:2014.
For mobile cranes on outriggers, stability depends critically on ground conditions. The typical outrigger pad exerts pressures of 50-200 kPa (7-29 psi). Engineering guidelines require soil bearing capacity assessments before crane setup, with mandatory use of timber mats or engineered cribbing when the pressures exerted by the crane exceed the allowable ground bearing pressure. Inadequate ground preparation is a leading cause of crane tipping accidents, particularly in construction sites with variable soil conditions.
Standards for cranes mounted on ships or offshore platforms are somewhat stricter because of the dynamic load on the crane due to vessel motion. For loads not associated with crewed operations, allowable loads must factor in dynamic accelerations including 1.75 g 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.
Dynamic Lift Factor
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. These effects include hoisting acceleration and deceleration of the load, crane movement such as slewing or luffing, swinging of suspended loads, wind forces acting on the crane, the load and the rigging, and operator error or other unexpected events.
The DLF for a new crane design can be determined with analytical calculations and mathematical models following the relevant design specifications. More sophisticated methods, such as finite 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 as load cells, accelerometers, and strain gauges. This process is usually part of the crane's type approval.
Jib cranes typically have a lower DLF (
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1.3
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) compared to traveling gantry cranes (
ψ
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1.6
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) because they are stiffer. For grab bucket cranes, the DLF can increase by 20% to 30% reflecting the shock loads caused by the release of the lifted material. The DLF generally decreases as the mass of the lifted object increases, as cranes tend to operate at lower velocities with heavier loads to ensure safety and stability.
In offshore lifting, where the crane and/or lifted object are on a floating vessel, the DLF is higher compared to onshore lifts because of the additional movement caused by wave action. Wave-induced vessel motions including heave, pitch, and roll are translated down the lifting wire, resulting in submerged loads being accelerated in response to forces induced by ship motions, with peak tension equal to weight plus inertial effects plus drag effects. The DLF further increases when lifting objects underwater or through the splash zone. For offshore lifts, the DLF typically decreases from 1.3 at 100 tonnes to 1.1 at 2500 tonnes as heavier loads require slower, more controlled operations.
Types
The crane types outlined in this section are categorized based on their primary area of application:
Construction
The most basic truck-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.
Larger, heavier duty, purpose-built "truck-mounted" cranes are constructed in two parts: the carrier, often called the lower, and the lifting component, which includes the boom, called the upper. 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. 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 and hoisting. 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 (or electronic 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.
Cargo handling
A reach stacker is a vehicle used for handling intermodal 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.
A sidelifter crane is a road-going truck or semi-trailer, able to hoist and transport ISO standard containers. Container lift is done with parallel crane-like hoists, which can lift a container from the ground or from a railway vehicle.
A travel 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. Not to be confused mechanical device used for transferring a vessel between two levels of water, which is also called a boat lift.
A Straddle carrier moves and stacks intermodal containers. It operates in a way similar to a gantry crane, but its purpose resembles a pick-and-carry crane, since it is used to move containers from one area to another.
Industrial
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 giant cantilever, crane is a fixed-jib crane consisting of a steel-braced tower on which revolves a large, horizontal, double cantilever; the forward part of this cantilever or jib 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. These cranes are generally constructed in large sizes and can lift up to 350 tons.
The design of Hammerkran evolved first in Germany around the turn of the 19th century and was adopted and developed for use in British shipyards 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 of battleships such as armour plate and gun barrels. Giant cantilever cranes were also installed in naval shipyards in Japan and in the United States. The British government also installed a giant cantilever crane at the Singapore Naval Base (1938) and later a copy of the crane was installed at Garden Island Naval Dockyard in Sydney (1951). These cranes provided repair support for the battle fleet operating far from Great Britain.
In the British Empire, the engineering firm Sir 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.
The Titan Clydebank is one of the four Scottish cranes on the River Clyde and preserved as a tourist attraction.
Normally a crane with a hinged jib will tend to have its hook also move up and down as the jib moves (or luffs). A level 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.
Marine
Floating cranes are used mainly in bridge building and port 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 on pontoons, others are specialized crane barges with a lifting capacity exceeding 10,000 short tons (8,929 long tons; 9,072 t) and have been used to transport entire bridge sections. Floating cranes have also been used to salvage sunken ships.
Crane vessels are often used in offshore construction.
The largest revolving cranes can be found on SSCV Sleipnir, which has two cranes with a capacity of 10,000 tonnes (11,023 short tons; 9,842 long tons) each. For 50 years, the largest such crane was "Herman the German" at the Long Beach Naval Shipyard, one of three constructed by Nazi Germany and captured in the war. The crane was sold to the Panama Canal in 1996 where it is now known as Titan.
Deck cranes, also known as shipboard or cargo cranes, 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.
Other types
A railroad crane has flanged wheels for use on railroads.
The simplest form is a crane mounted on a flatcar. More capable devices are purpose-built. Different types of crane are used for maintenance work, recovery operations and freight loading in goods yards and scrap handling facilities.
Aerial cranes or "sky cranes" usually are helicopters 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 as airships.
Efficiency increase of cranes
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.
Similar machines
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'.
Types of crane-like lifting machine include:
More technically advanced types of such lifting machines are often known as "cranes", regardless of the official definition of the term.
Notable Examples
Finnieston Crane, a.k.a. the Stobcross Crane
Category A-listed example of a "hammerhead" (cantilever) crane in Glasgow's former docks, built by the William Arrol company.
50 m (164 ft) tall, 175 tonnes (172 long tons; 193 short tons) capacity, built 1926
Taisun
double bridge crane at Yantai, China.
20,000 tonnes (22,046 short tons; 19,684 long tons) capacity, World Record Holder
133 m (436 ft) tall, 120 m (394 ft) span, lift-height 80 m (262 ft)
Kockums Crane
shipyard crane formerly at Kockums, Sweden.
138 m (453 ft) tall, 1,500 tonnes (1,500 long tons; 1,700 short tons) capacity, since moved to Ulsan, South Korea
Samson and Goliath (cranes)
two gantry cranes at the Harland & Wolff shipyard in Belfast built by Krupp
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
Breakwater Crane Railway
self-propelled steam crane that formerly ran the length of the breakwater at Douglas.