MEGASTRUCTURES: Capital Gate (The Leaning Tower of Abu Dhabi)

MEGASTRUCTURES: Capital Gate (The Leaning Tower of Abu Dhabi): National Geographic Channel

by Simon Zohhadi on Wednesday, 13 October 2010 at 18:35 ·

Desription: New Leaning Skyscraper. Lean is 5 times greater than the Leaning Tower of Pisa. 400 Concrete plies with 200 under the opposite side of the lean placed at a greater depth to withstand stress forces. Reinforced concrete slab forming the base of the tower.

Normal skyscrapers built around a solid inner core to provide structural stability and thereby holding it upright. However, this leaning skyscraper required a new solution that would defy gravity. The curved leaning skyscraper was built with a concrete inner core which was built curving in the opposite direction of the lean of the building. As the structure increased in height the weight of the building pulled the concrete core straight. The shift was 350 mm. Each slab pulled the core back to the centre.

The core was built at a rate of 4 metres a week by jump forming; a dense form of mesh steel reinforcement encased by a mould forming the shape of the inner core. The steel mesh is then filled with concrete. The mould then rises up to the next level. The steel rods (rebar) reinforce the core.

Problem. High temperatures during the day were too hot causing the concrete to set too quickly causing cracking. Therefore, the concrete work had to be carried out during the night. Each batch of concrete had to be tested using the slump test. The slump of 250 mm was within the specification tolerances.

The outside core was made up of a diagrid with 720 steel cruciforms weighing 16 tonnes each. Pinpoint on-site assembly was necessary to ensure loads were evenly distributed. This steel grid was clad with a glass facade. Each pane (26,000 in number) was triangular in shape, forming diamond shapes. The excessive movement of the skyscraper whilst it was being built required glass panels that were capable of shifting up to 20mm to ensure water tightness and preventing cracking. The rubber seals between each diamond allowed for movement and internal drainage channels ensured that the building remained water tight.

A restaurant and swimming pool was built overhanging the outside of the skyscraper at a height of 100 metres. This extension was supported by 22 steel struts that carried the loads into the building.

An internal web of steel mirrored the diagrid and carried forces down the building into the core. The core was protected by 6 steel plates.

Problem: Wind conditions made installing glazed panels difficult and this caused a delay until conditions changed. Each diamond panel weighed 4 tonnes. Final panel was installed 10 months after the first.

Last minute design change / client request: Helipad on top of building. This had design problems due to suction forces lifting the helipad and wind forces making landing difficult. The solution was to install the helipad only 2 metres above the roof.


Internal fit-out took another year.

The building was 162 metres in height and took 6 million man hours to build.


Planned Programme: Design and Build = 24 months