The secret gets harder to keep as the tower, now at about 80 stories, rises toward its pinnacle, at an average of one floor every three days. Whatever its final stopping point, Burj Dubai is on course to supersede the world record holder, the 509-m-tall Taipei 101, by summer, says Greg Sang, assistant director for projects at local owner Emaar Properties PJSC.
The largely residential and hotel burj—Arabic for tower—already surpasses Europe’s tallest building, Moscow’s 264-m Triumph-Palace. Located just south of the United Arab Emirate city, the iconic centerpiece of Emaar’s $20-billion Burj Dubai Down- town mixed development, is taking the form of a tapering, three-winged tower, mainly of over 280,000 cu m of concrete rising 162 floors. From level 156, the tower will be framed with some 0.5 million tonnes of structural steel in equipment floors and the spire.
The steel frame alone will be “almost as tall” as the U.K.’s tallest building at London’s Canary Wharf, which is 225 m, says Rob Pickering, project director of Hyder Consulting Middle East Ltd., the tower’s construction supervisor and designer of record.
The reinforced concrete structure serves the quest for height of Emaar, which is a third owned by Dubai’s ruling family. But it meant taking wind engineering to new heights. “We virtually designed the tower in a wind tunnel,” says Bill Baker, structural partner at architect-engineer Skidmore, Owings & Merrill LLP, Chicago. “In the old days, wind tunnels were for confirmation of forces, not to tell you what the building would look like.”
Adds Anton Davies, a director of Burj Dubai’s wind consultant, Rowan Williams Davies & Irwin Inc. (RWDI), Guelph, Ontario: “We probably did a million dollars worth of work on this.”
The largely residential tower’s smaller room sizes allowed greater use of structural walls than would have been possible for an office building, notes Eric Tomich, SOM’s associate partner on site. Having designed a broadly similar structure for Korea’s 264-m-tall Tower Palace III a few years ago, Baker says “we knew we could get this structural system pretty damn high. Essentially, every piece of vertical concrete is part of the lateral system.”
The stiff, six-sided core will reduce twisting to below residents’ discomfort threshold. Lateral stability comes from pairs of roughly 60-centimeter-thick, reinforced concrete shear walls forming central corridors of the three symmetrically distributed wings.
Lower wings, which project over 60 m from the core, shorten in turn by 9-m bays creating 27 setbacks spiralling up the tower. Perimeter columns, generally 1.9 m in diameter, support outermost bays.
The constantly changing profile may complicate construction but it prevents the building from resonating to wind-induced vibrations. Vortex shedding “is going to happen, but you don’t want it organized,” says Baker.
Shear walls at the tower’s two-floor- deep mechanical levels act as outriggers. The four levels of complete outriggers, and one partial, mobilize all vertical elements to resist lateral loads.
Wind consultant RWDI worked with SOM during design to refine the shape and orientation. Using local and regional wind data, RWDI proved the original 45-m-per-sec design wind speed would be excessive. Based on the data, authorities allowed a design wind speed over 15% lower than the value set by their interpretation of the local code, says Peter Irwin, RWDI’s president. Otherwise, it “would certainly have been a much more expensive structure,” adds Baker.
Tower was virtually designed in wind tunnel, says engineer.
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