Opening of Dubai’s Burj Khalifa in January 2010 was a resounding answer to those who had challenged whether tall buildings would ever be built again following the unthinkable collapse of the World Trade Center towers in New York nine years earlier.
Officially confirmed as the world’s tallest building, the 828m tall Burj Khalifa surpassed the previous “World’s Tallest”, Taipei 101 in Taiwan, by 320m − an unprecedented increase of 61%.
The Burj Khalifa has also surpassed previous record heights in the “Height to Tip” and “Highest Occupied Floor” categories at 829.84m and 584.50m respectively. The building also contains a record breaking number of floors, at 163 − a record previously held by the World Trade Center towers at 110 floors.
Building such a super-tall tower, even in the cash-rich world of Dubai, was no easy task. Workers were unskilled and many didn’t speak English or Arabic. Materials had to be shipped from around the globe and delivered to a site which – incredibly – had no room for storage. The cladding contractor went bust midway through construction. And most seriously of all, the concrete floor slabs sagged early in construction and had to be beefed up with carbon fibre strips steel I-beams. It is widely reported that they were designed as prestressed but in fact poured as simply reinforced, and as a result were too shallow and light on reinforcement. In total floors five to 15 needed beefing up.
The tower was built for developer Emaar Properties by South Korean company Samsung. Skidmore, Owings & Merrill (SOM) of Chicago led the architectural, structural engineering and mechanical engineering design team. Hyder Consulting was the client’s engineer and Turner International the project manager. Work began on site on 1 February 2005.
Constructing the concrete core involved an unusually high proportion of wall-forming operations for a skyscraper. Its honeycombed design meant forming 430,000m² of walls – twice the area of the floor-slabs. A typical storey was finished every three days. Doka provided the formwork, and its system proved exceptionally robust.
Climatic conditions encountered at the site were often extreme: the desert climate next to the open sea causes great temperature fluctuations between day and night, and this can lead to violent sandstorms with wind speeds of over 100 km/h. Daytime temperatures often hit 50°C so concrete was poured only at night - and even then ice often had to be added to the mix to keep temperatures down.
Following the WTC attacks, fire safety on the Burj was always going to be a top priority. The building has been designed to evacuate 35,000 people, more than twice its expected occupancy. Evacuation is by stairs, and it’s a long way down from 160 storeys – so pressurised air-conditioned refuge areas are located every 25 floors for evacuees to rest or await rescue.
Opening of the Burj coincided with the global financial meltdown. As a result several other major projects in the region that were threatening to topple the Burj’s status as world’s tallest have been mothballed. Kuwait had plans to construct the 1,001m tall Burj Mubarak Al-Kabir tower; Emaar’s chief rival Al Nakheel was planning a gazumping on a grand scale with Al Burj, a tower set to top 1,050m and possibly reach 1,200m; and Saudi unveiled plans for a 1.6km-high whopper.
But Emaar took the threats so seriously that even during construction the final height of the Burj was top secret – and changed several times.
“Our original [design] was only slightly taller than Taipei,” remembers Skidmore Owings Merrill partner in charge of structural and civil engineering Bill Baker. “We didn’t want to promise tallest. But we thought with a few changes here and there, we could really go high. Then the client asked us to go higher. We were cautious and said we’d do our best. Even after the foundations went in, we went higher. Emaar changed the brief several times. We refined, redesigned and reduced loads.”