Friday, 5 February 2016

Confuses The Wind To Bag The World's #1 Supertall Skyscraper?


Last winter holiday, we took a cab at 5 am from Jumeirah Lake Tower for the world’s iconic Burj Khalifa to watch the sunrise. Yes, early risers! (Hats off to myself) At the height of 828m, Burj Khalifa is world’s tallest free-standing building, the highest number of stories, highest occupied floor and also highest observation deck. The height of Taipei 101 (508m) and Chrysler (320m) building in New York on top of it is equivalent to the height of Burj Khalifa!


Looking across the horizon from At the Top observation deck looks like these (time was between 6.10 am - 6.55 am).

At the Top observation deck is on level 124 which is approximately 452m in height. The temperature sets around 13 degree Celsius while the wind blows around 1m/s to 6m/s, yes, the cold gritted to the bone as we were dressed in thin layers!


Breathtakingly, the bright sun peaks on the horizon across the desert and fully rises approximately at 7.04 am. 


Like a guitar string, a building has a natural frequency or resonant at which they inclined to vibrate. Tuned mass damper, harmonic absorber, is a device mounted in structures to reduce the amplitude of mechanical vibrations. It is a mechanical solution to alleviate wind stress, ensure structural stability and guarantee the comfort of occupants. The tuned mass damper is also used to address acceleration and peoples’ queasiness and response to the sway of the building. This helps Taipei 101 tower, at the height of 508m to be stable and acquire them second in the line of a super tall skyscraper. 


But Burj Khalifa has no tuned mass damper to absorb the wild desert wind, how can the tower be stable when the height is ridiculously high? 

Confusing the wind is one of the methods in a structural solution used to help supertalls resist wind stress. The building rises in several separate stalks, shape changes along the height of the building so the flow pattern cannot recognize itself. The design is based on Hymenocallis flowers, common name “spider lily”. This shape design is to abolish the resonance from wind to the building. It deflects the wind around the structure and prevents it from forming an organized whirlpool of current, or vortices that would rock the tower from side to side and could even damage the building. Disrupting the organized flow of the wind around the building, so the flow pattern can’t organize itself. [Photo credit: http://www.munchkinnursery.com/newsletter-past-year-titles-recent-titles-spider-lily]



500- Or 1000- year return rule.  Wind engineering experts work hand in hand with the building’s engineers prior to construction constructing a complex, rigid scale model for testing for wind data collection. Skyscrapers are engineered to this return rule, expecting winds to reach structurally dangerous speed once in a half millennium or more. Jason Garber, a wind engineering specialist at RWDI, a leading wind tunnel testing firm says that this building isn't in any risk of falling over. 
Yes, Burj Khalifa, astounding as it sounds this urban design made possible with an extensive structural solution of confusing the wind with its non-repetitive design along its height, and engineered to millennium return rule. Shall we predict even higher skyscraper to top Burj Khalifa in next ten years’ time? I might be writing about it then:)


Glossary
1. Abolish - formally put an end to
2. Frequency - number of occurrences of a repeating event per unit time
3. Resonance - phenomenon that occurs when a vibrating system or external force drives another system to oscillate with greater amplitude at a specific preferential frequency
4. Queasiness - uneasiness, nausea

References:
1. http://www.studentpulse.com/articles/124/confusing-the-wind-the-burj-khalifa-mother-nature-and-the-modern-skyscraper
2. http://www.emirates247.com/news/emirates/burj-monument-celebrates-making-of-burj-khalifa-2012-03-20-1.449491
3. http://ikb.edu.pl/jacek.wdowicki/Pliki/materialy/dydaktyka/budynki_wysokie/dyplom/budynki/burj%20dubai%20tower/Irw05.pdf
4. http://www.lib.washington.edu/specialcollections/collections/exhibits/tnb
5. http://www.wsdot.wa.gov/tnbhistory/connections/connections3.htm
6. http://www.burjkhalifa.ae/en/the-stories.aspx



Shared by Hani Nordin
Guest Blogger


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