How Peter Irvin, a renowned wind engineering expert, saved Burj Khalifa from the Wind
Hobbes S Sujith is a writer at Advenser, a company specialized in offering BIM services.
Burj Khalifa became the tallest skyscraper on the earth during its construction phase when it reached 512m and 141 floors. The architects and engineers had no intention of stopping and planned to reach 830m. When Burj Khalifa was reaching for the sky, it was entering into the unknown, but one powerful force soon started to become an increasing threat - wind force.
George Efstathiou, Managing Architect at SOM (Skidmore, Owings and Merrill LLP) for Burj Khalifa said that “First thing you need to understand in general is, you need to be very respectful of the laws of the nature like wind, heat and the gravity. When the skyscrapers reach this height, the most dangerous and unpredictable elements is wind. At these heights, the dominant load is neither dead load nor live load, its wind load. When the wind blows on the side of the skyscraper, it definitely tends to bend the skyscraper trying to push it over
Why wind force can’t be ignored for Skyscrapers – John Hancock Tower
John Hancock Tower (240m), a 60 story skyscraper in Boston demonstrates the problem better. In 1976, when the construction of the building was completed, it was a sheer masterpiece of steel and glass. However, it showcases a serious problem. People in the building suffered motion sickness, as the building swayed in the moderate wind. To make the situation worse, glass panels began to fall from the building’s façade. 10,344 glass panels got fractured when a strong wind hit Boston during the construction in 1973. Windowpanes weighing 227kg (1.2 X 3.4m) detached from the building and crashed down to the sidewalk, damaging window panes on the way down. Surrounding streets and sidewalks were instantly cordoned off by the police, an action which is repeatedly taken when the winds speed reaches 45 mph (72 km/h).
Eventually the engineering flaws at John Hancock Tower were rectified with:
How Burj Khalifa was prevented from suffering the similar fate of John Hancock Tower
- Mass dampers
- Reflective glass – oscillation and repeated thermal stress caused by the expansion and contraction of the air between the inner and outer glass panels
- Diagonal steel bracing.
Wind loading and wind-induced motions were expected to be severe for Burj Khalifa - due to a slender structural design. At the inception of the design process RWDI was hired for the task under the direction of Dr. Peter Irwin. The original design for the building was around 300m shorter, similar in concept to what we see today. However the challenge for Peter’s team increased as goals on the project changed, at which point the construction for the foundation had already begun.
The wind engineering team wanted to know two aspects.
- What are the winds doing in the area where the Burj Khalifa is going to be built?
- What is the wind going to do to the Burj Khalifa?
Peter and the wind engineering team calculated that the Burj Khalifa needed to withstand gusts of up to 240 km/h. At 828m, Burj faces an additional threat - when skyscrapers get taller and slender the buildings runs into a phenomenon called vortex shedding. Due to this phenomenon, vortex peeling takes place from the front corner first and then from the other side. As the whirlwinds peel off each side of the skyscraper, they can easily pull the building from side to side. Peter and team need to take these things into account.
With the impact of wind tunnel testing, Peter and the team came up with 3 aerodynamic improvements that were later developed.
- Improve the shape of the outer buttresses by softening the corners
- Reduce the width of the tower at higher levels
- Reorienting the entire tower relative to the prevailing wind directions.
The end result of these aerodynamic improvements was an incredibly stable skyscraper. A unique shape which resists the vortex shedding. In fact, you could definitely say that Burj Khalifa comes with a shape whereby the wind is unable to create the strong cross forces that affect other buildings. When inaugurated on 4th January 2010, it was the tallest structure in the world. An excellent example of successful collaboration of structural systems, wind engineering, and architectural aesthetics.
Hobbes S Sujith is a writer at Advenser, a company specialized in offering BIM services. He devotes his time to inspire his team. With 10+ years of experience as a writer and digital marketing specialist, he now focuses on the AEC sector by providing digital marketing solutions.
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