Capital Gate
FOUNDATION
The steel exoskeleton known as the diagrid sits above an extensive distribution of 490 piles that have been drilled 100 feet underground to accommodate the gravitational, wind and seismic pressures caused by the lean of the building.Of the total 490 piles, 287 were 1m (40in) in diameter, and 20-30 meters (65-100 feet)deep, the remaining 193 piles had a diameter of 600mm (24 inches) with a depth of 20m (65 feet). Unlike most buildings, whose piles are in compression, the piles for Capital Gate are in tension.
This was done to help resist the upward forces that would tend to pull the pile out of the ground. The building, however, cannot sit directly on top of the piles. All 490 piles were capped together using a densely reinforced concrete mat footing of nearly 2 meters deep.The piles, which were initially in compression during construction to support the lower floors of the building, are now in tension as the stresses caused by the overhang have been applied.The piles were of two different sizes one.To help counteract the large overturning moment, which is caused by the buildings lean and other to anchor and transfer load into the soil.The piles act in two ways, half of the piles in the leaning side pushes the overhanging stresses in to the ground and on the opposite side the piles just transfer the load into the grounds.
CORE
Core of the capital gate is built using jumping form work. The center concrete core had to be specially designed to account for the immense forces created by the building’s lean. The core, which contains 15,000 cu.m (19,619yd2) of concrete reinforced with 10,000 tons of steel, uses vertical post-tensioning and was constructed with a vertical pre-camber. This pre-camber means that the core was constructed with a slight opposite lean, as each floor is installed, the weight of the floors and diagrid system pull the core and slowly straightening it out. For post tensioning 146 steel tendons are vertically placed in the concrete core each 20 mts long which overlaps each other, never done before in a skyscraper. These tendons were used for post tensioning vertical cables in one side tensioned to counteract the lean on the other side. It is displaced for a distance of 350 mm. The Vertical Post tensioning is done for the lateral stability of the structure.
SUPERSTRUCTURE
The capital gate employs a fine grid that fits this 160m tower, Diagrid made construction of this tower possible given its lean of 18 degree. Overall the ability to have smaller diagonal patterns(provided the diagrids helps the tower to blend it with the surroundings avoiding brutal aesthetics. There are two diagrid systems, an external diagrid defining the tower’s shape and an internal diagrid linked to the central core by eight unique pin-jointed structural members.The external diagrid consists of 720 sections each of different shape as it is based on the direction in which it leans. The external grid carries the weight of the floor while the internal digrid connects with the external and transfers the load to the core.
To make this possible, the central core of the building slants in the opposite direction to the lean of the structure, and it straightens as it grows.
Core of the structure is attached to the internal grid which connects external diagrid through steel girders therefore creating no columns.
This project used 6.5 million hours, started from september 2007 finished by the end of 2010, actually delayed by 5.5 months.
I really find this structure to be fascinating as it it has taken civil engineering to a whole new level.!!!
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