21-09-2016, 02:43 PM
use of cranes and advantage and disadvantages of crane
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advantage and disadvantages of crane pdf
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use of cranes and advantage and disadvantages of crane
22-09-2016, 09:07 AM
Cranes are a family, Gruidae, of large, long-legged and long-necked birds in the group Gruiformes. There are fifteen species of crane in four genera. Unlike the similar-looking but unrelated herons, cranes fly with necks outstretched, not pulled back. Cranes live on all continents except Antarctica and South America.
They are opportunistic feeders that change their diet according to the season and their own nutrient requirements. They eat a range of items from suitably sized small rodents, fish, amphibians, and insects to grain, berries, and plants.
Cranes construct platform nests in shallow water, and typically lay two eggs at a time. Both parents help to rear the young, which remain with them until the next breeding season.[1]
Some species and populations of cranes migrate over long distances; others do not migrate at all. Cranes are solitary during the breeding season, occurring in pairs, but during the non-breeding season they are gregarious, forming large flocks where their numbers are sufficient.
Most species of cranes have been affected by human activities and are at the least classified as threatened, if not critically endangered. The plight of the whooping cranes of North America inspired some of the first US legislation to protect endangered species.
They are opportunistic feeders that change their diet according to the season and their own nutrient requirements. They eat a range of items from suitably sized small rodents, fish, amphibians, and insects to grain, berries, and plants.
Cranes construct platform nests in shallow water, and typically lay two eggs at a time. Both parents help to rear the young, which remain with them until the next breeding season.[1]
Some species and populations of cranes migrate over long distances; others do not migrate at all. Cranes are solitary during the breeding season, occurring in pairs, but during the non-breeding season they are gregarious, forming large flocks where their numbers are sufficient.
Most species of cranes have been affected by human activities and are at the least classified as threatened, if not critically endangered. The plight of the whooping cranes of North America inspired some of the first US legislation to protect endangered species.
30-07-2017, 09:08 AM
02-08-2017, 02:22 PM
A crane is a type of machine, usually equipped with a hoist rope, wire ropes or chains and pulleys, which can be used both to lift and lower materials and to move them horizontally. It is mainly used to lift heavy things and transport them to other places. The device uses one or more simple machines to create mechanical advantages and therefore move loads beyond the normal capacity of a human being. Cranes are commonly employed in the transportation industry for loading and unloading cargo, in the construction industry for the movement of materials and in manufacturing for mounting heavy equipment.
The first known construction cranes were invented by the ancient Greeks and were driven by men or beasts of burden, such as donkeys. These cranes were used for the construction of tall buildings. The larger cranes were developed later, employing the use of human wheel wheels, allowing the lifting of heavier weights. In the High Middle Ages, harbour cranes were introduced to load and unload ships and help with their construction - some were built on stone towers for extra strength and stability. The first cranes were built from wood, but cast iron, iron and steel took over the arrival of the Industrial Revolution.
For many centuries, power was supplied by the physical effort of men or animals, although hoists in water mills and windmills could be driven by the natural power harnessed. The first "mechanical" energy provided by the steam, the steam crane earlier introduced in the eighteenth or nineteenth century, with many remain in use either late twentieth century. Modern cranes generally use internal combustion engines or electric motors and hydraulic systems to provide a capability much greater elevation than previously possible, although manual cranes are still used where the power supply is uneconomical.
Cranes exist in a huge variety of forms - each adapted to a specific use. Sizes range from the smallest pen cranes used in the workshops to the tallest tower cranes used for the construction of tall buildings. The mini-cranes are also used for the construction of tall buildings, in order to facilitate the constructions by means of the access to reduced spaces. Finally, we can find larger floating cranes, generally used to build oil rigs and to save sunken ships. Some lifting machines are not strictly fit the above definition of a crane, but are generally known as cranes, such as stacker cranes and loading cranes.
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