Quote:
Originally Posted by Canadian Mind
Doesn't looks to me to be very many concrete supports to hold all 808 meters of the thing up in the air. How can such a small amount of concrete hold so much weight up?
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It's deceptive how thick those outer columns are. There are four columns in each of the first 3 setbacks that are over 5 feet wide in diameter, steel reinforced concrete (of the highest quality).
These first columns only have to support the outer levels above from levels 0-19,26 and 34 respectivley. These columns also take transferred loads from the much thicker 17th-19th mechanical floors hense why they are so thick!
The next set of setbacks (4,5 and 6) have only 2 outer columns over 7 and a half feet thick (about the same in volume as the previous setbacks) again only supporting levels from 19-43, 26-53 and 34-64, with similar load transfers in the mechanical levels between L41-L43.
The box matrix between these setbacks and the haxagonal core only have to contend with mainly compressive forces from the floors above.
Every delivery of concrete is sampled in a 10 cm core before delivery, set and put into a compression testing rig, to determine its performance during compression and is tested to distruction.
At different levels and for different purposes the concrete will be mixed to different mixtures, with different additives, both chemically and in composition to determine the required matrix.
If you had just 12 match sticks and securely bound the corners together to form a cube, then stood on top of it, equally distributing your weight across the surface, it will happilly support your body weight until any kind of lateral load was imposed upon it.
It's the same with this tower, the columns are strong enough to hold the tower to a height of 3kms, but lateral loads, earthquake proofing, torsional rigidity, wind loads, age degradation and fatigue all have to be taken into consideration + 30% for error and design change.
Because the tower is so high and is predominently residential, lateral forces are kept to a minimum by using concrete. This is why steel is being used towards the top. Cheaper, faster to construct, pre assembleable, and a lighter load per square meter with the flexability of design change in the later stages of construction.