How tower cranes work ?

These big birds of sky-high construction are engineering marvels

Tower cranes ﬂ ock to money. During the economic boom years, high-rise construction cranes migrated from Beijing to Shanghai to Dubai, where it was estimated in 2006 that there was one tower crane for every 44 residents of the desert boom-opolis. Tower cranes are feats of structural engineering that often outshine their creations. They are designed to stand 80 metres tall and reach 80 metres out supported only by a narrow steel-frame mast, a concrete foundation and several counterweights. The engineering principle that keeps the twiggy tower crane from tipping over is something called a ‘moment’. If you hang a weight from the crane’s jib arm, it exerts a

rotational force or torque where the arm connects to the top of the mast. The magnitude and direction of this force (clockwise or anticlockwise) is called the moment. If the weight is hung close to the mast, the magnitude of the moment is lower than if the weight is hung far out on the jib. To keep the crane upright, counterweights are used to create a moment of equal magnitude in the opposite direction, balancing out the rotational forces. Once a tower crane meets its maximum unsupported height, it can be tethered to the building itself and continue to grow with the rising skyscraper. The tower cranes that rose with the construction of the record-breaking Burj Khalifa skyscraper in Dubai reached a truly dizzying height of 750 metres.

Self-assembling crane

One of the most remarkable engineering feats of tower cranes is that they can literally build themselves. With help from a large mobile crane, construction workers secure the base sections of the tower and assemble the top unit of the crane – the slewing unit, jib and machinery arm. But before the top section of the crane is attached, workers slide a hydraulic climbing unit around the base of the tower. Once everything is in place, the hydraulic climbing unit lifts the entire top section of the crane (including the horizontal jib and operator’s cab) just enough to slide in a new section of tower beneath. Once the new section is secured, the hydraulic unit continues to climb up, section by section, as the crane slowly builds itself higher.

Comments

Why do the Indian telecom operators offer their services with 28 days validity, not 30 days?😡😡

Here telecom operator are very clever, b ecause telecom operators want to earn money of 13 months instead of 12 months. Let do the calculation and find out why telecom operators are offering 28 days validity. Each month they get 2 days more, therefore in a year they get additional 24 days. There are 7 month which has 31 days so they get additional 7 days.Now in case of February ,it has only 28 days not 30. So the total number of days they get are=24+7-2=29 days. So if you recharge 12 times then more 29 days are left in a year.🤔🤔 Means for another 29 days you have to recharge from that telecom operator.😫😫 So you have to recharge 13 times in a year instead of 12 times in a year. So telecom operators provide 28 days validity only. First one telecom operator started and then another telecom operators also understood this concept and they also applied 28 days validity both in data packs and voice packs.😱😱😱

20 Interesting science fact (PART 1)

1/ The speed of light is generally rounded down to 186,000 miles per second. In exact terms it is 299,792,458 m/s (metres per second - that is equal to 186,287.49 miles per second). 2/ It takes 8 minutes 17 seconds for light to travel from the Sun's surface to the Earth. 3/ October 12th, 1999 was declared \\"The Day of Six Billion\\" based on United Nations projections. 4/ 10 percent of all human beings ever born are alive at this very moment. 5/ The Earth spins at 1,000 mph but it travels through space at an incredible 67,000 mph. 6/ Every year over one million earthquakes shake the Earth. 7/ When Krakatoa erupted in 1883, its force was so great it could be heard 4,800 kilometres away in Australia. 8/ The largest ever hailstone weighed over 1kg and fell in Bangladesh in 1986. 9/ Every second around 100 lightning bolts strike the Earth. 10/ Every year lightning kills 1000 people. 11/ In October 1999 an Iceberg the size of London broke free...

A brief history of the Morse code

££) In the early nineteenth century, all of the essential components necessary to construct an electrical communication system had been discovered. The most important of these were the battery by Volta, the relationship between electric current and magnetism by Oersted, and the electromagnet by Henry. It now remained for someone to find a practical method to combine these technologies into a working communication system. ££)Some commercial electrical communications systems existed in Europe as early as the 1830s. A classic example of this is the English ‘Needle Telegraph’. The needle telegraph required two or more lines to form a complete circuit. It was relatively slow and the design of the transmitting and receiving instruments was complex. Something simple and efficient was needed. ££)The Morse system of telegraphy was invented by Samuel Finley Breese Morse (an American painter and founder of the National Academy of Design in New York) in the 1840s ...

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