毕业设计方案中起重机的英文翻译Word文件下载.docx

1、The first construction cranes were invented by the Ancient Greeks and were powered by men or beasts of burden, such as donkeys. These cranes were used for the construction of tall buildings. Larger cranes were later developed, employing the use of human treadwheels, permitting the lifting of heavier

2、 weights. In the High Middle Ages, harbor 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 and steel took over with the coming of the In

3、dustrial 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 th

4、e 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 wher

5、e the provision of power would be uneconomic.Cranes exist in an enormous variety of forms 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. For a while, mini - cranes are also used for

6、constructing high buildings, in order to facilitate constructions by reaching tight spaces. Finally, we can find larger floating cranes, generally used to build oil rigs and salvage sunken ships. This article also covers lifting machines that do not strictly fit the above definition of a crane, but

7、are generally known as cranes, such as stacker cranes and loader cranes.2. HistoryAncient GreeceThe crane for lifting heavy loads was invented by the Ancient Greeks in the late 6th century BC. The archaeological record shows that no later than c.515 BC distinctive cuttings for both lifting tongs and

8、 lewis 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

9、as the positive evidence required for the existence of the crane. The introduction of the winch and pulley hoist soon lead to a widespread replacement of ramps as the main means of vertical motion. For the next two hundred years, Greek building sites witnessed a sharp drop in the weights handled, as

10、 the new lifting technique made the use of several smaller stones more practical than of fewer larger ones. In contrast to the archaic period with its tendency to ever-increasing block sizes, Greek temples of the classical age like the Parthenon invariably featured stone blocks weighing less than 15

11、-20 tons. Also, the practice of erecting large monolithic columns was practically abandoned in favor 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

12、 of Greece were more suitable to the employment of small, professional construction teams than of large bodies of unskilled labor, making the crane more preferable to the Greek polis than the more labor-intensive ramp which had been the norm in the autocratic societies of Egypt or Assyria. The first

13、 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 archa

14、ic predecessors again, indicating that the more sophisticated compound pulley must have found its way to Greek construction sites by then. Ancient RomeThe heyday of the crane in ancient times came during the Roman Empire, when construction activity soared and buildings reached enormous dimensions. T

15、he Romans adopted the Greek crane and developed it further. We are relatively well informed about their lifting techniques, thanks to rather lengthy accounts by the engineers Vitruvius （De Architectura 10.2, 1-10 and Heron of Alexandria （Mechanica 3.2-5. There are also two surviving reliefs of Roman

16、 treadwheel cranes, with the Haterii tombstone from the late first century AD being particularly detailed.The simplest Roman crane, the Trispastos, consisted of a single-beam jib, a winch, a rope, and a block containing three pulleys. Having thus a mechanical advantage of 3:1, it has been calculated

17、 that a single man working the winch could raise 150 kg （3 pulleys x 50 kg = 150, assuming that 50 kg 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 （Polysp

18、astos and came with two, three or four masts, depending on the maximum load. The Polyspastos, when worked by four men at both sides of the winch, could already lift 3000 kg （3 ropes x 5 pulleys x 4 men x 50 kg = 3000 kg. In case the winch was replaced by a treadwheel, the maximum load even doubled t

19、o 6000 kg 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 Egyptian Pyramids, where about 50 men were needed to move a 2.5 ton stone block up the ramp （50 kg per person, the

20、lifting capability of the Roman Polyspastos proved to be 60 times higher （3000 kg per person. 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

21、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. In Rome, the capital block of Trajans Column weighs 53.3 tons, which had to be lifted to a h

22、eight of about 34 m （see construction of Trajans ColumnIt 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

23、of a quadrangle with parallel sides, not unlike a siege tower, but with the column in the middle of the structure （Mechanica 3.5. Second, a multitude of capstans were placed on the ground around the tower, for, although having a lower leverage ratio than treadwheels, capstans could be set up in high

24、er numbers and run by more men （and, moreover, by draught animals. This use of multiple capstans is also described by Ammianus Marcellinus （17.4.15 in connection with the lifting of the Lateranense obelisk in the Circus Maximus （ca. 357 AD. The maximum lifting capability of a single capstan can be e

25、stablished 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. Lifting such heavy weights in a concerted action required a grea

26、t amount of coordination between the work groups applying the force to the capstans.Middle AgesDuring 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 r

27、eference 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, Brugg

28、e 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 tr

29、eadwheel 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 medieva