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USGNN Original StoryGlass Installation Continues on Abu Dhabi's Spiraling Capital Gate Tower
July 20, 2009

Considered by some to be one of the world's most challenging buildings under construction, the Abu Dhabi National Exhibition Company's (ADNEC) Capital Gate project recently passed the halfway mark. The tower, which leans 18-degrees westward-14 degrees more than the Leaning Tower of Pisa-includes a giant internal atrium suspended on the 17th and 18th floor; the façade comprises 23,000 square meters of steel and glass elements spiraling skywards.

The $35 million glass facade is the responsibility of Austria's Waagner-Biro, which is handling the steel and glass engineering. According to RMJM, the United Kingdom-based architectural firm that designed the project, the façade will feature Cardinal C240 glass that is being shipped from the United States straight to Abu Dhabi, though at press time RMJM representatives could not confirm what company is actually supplying the glass. (Editor's note: USGNN.com™ contacted Cardinal Corp. for additional information, but at press time had not received a response.)

The design of the building poses several challenges with regards to planning, production and erection. In keeping with the triangular configuration of the main supporting structure, more than 700 diamond shaped glass panels will be prefabricated on site from triangular tubes and lifted into position fully glazed. No two of the 12,000 triangular panels are alike.

Because of the tower's unique posture, the 35-story Capital Gate is being constructed on top of a 2-meter deep concrete raft with an extremely dense mesh of reinforced steel. The steel exoskeleton known as the "diagrid" sits above an extensive distribution of 490 piles that have been drilled 30 meters underground to accommodate the gravitational, wind and seismic pressures. The design of the central core, which slants in opposition to the lean of the building, straightening as it grows, has never been attempted before.

The diagrid technology has only been used on a few buildings, including the Hearst Tower in New York, The Gherkin in London and the CCTV headquarters tower in Beijing. The system requires less structural steel than a conventional steel frame and is formed by creating triangular structures with diagonal support beams.

The total weight of Capital Gate's steel is estimated to be around 21,500 tons. Its diagrid is subdivided into 722 elements and approximately 8,500 structural steel beams for the entire building. Each diagrid element weighs approximately 15 tons.

The building's decorative 'splash' is designed to mimic a wave. Besides providing an innovative sunshade for the Capital Gate tower itself, the splash provides a new and creative treatment for the roof of the existing grandstand canopy in the adjoining Abu Dhabi National Exhibition Centre grandstand. The splash is a completely independent structure made of structural steel I-beams fixed to the main building structure.

"The unique nature of this building has meant that the teams responsible for delivering Capital Gate have experienced some immense challenges, which they have overcome through vision, ingenuity and cooperation. There is nothing standard about this tower. Each room is different, each pane of glazing is different and every angle is different," says Simon Horgan, ADNEC group chief executive officer.

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