Structural design concepts of Burj Khalifa

August 30, 2022

ABOUT THE AUTHOR

Namrata Karande was working as a Product developer : Civil Engineer at Lesics Engineers Pvt. Ltd. Namrata has worked on projects such as Footing, Hoover dam and Burj khalifa.


The Burj khalifa project is the tallest structure ever built by humans. The Burj Khalifa stands strong on loose, sandy soil braving the strong Arabian winds is truly a modern engineering marvel. In this article we are going to explore all the design secrets and interesting facts of the world’s tallest building.

The height of Burj Khalifa is 828 meters (2716.5 ft). How the engineers achieved this incredible height, because as the height of any structure increases its stability challenges become difficult to achieve as the wind speeds are higher. Let's start with its surprisingly simple hexagonal core.

Structural design concepts of Burj Khalifa

The soul of the Burj Khalifa is its hexagonal core as shown in Fig 1. This RCC-built core is enabling the Burj Khalifa to keep standing despite the devastating wind storms of Dubai, and helps keep the weight of the building balanced. The hub also accommodates the entire lift system of this building. The elevators of Burj Khalifa are the world's fastest elevators and it covers the longest travel distance.

Fig 1 : Hexagonal core of burj khalifa

Structural analysis

If this core was alone, it would have been highly unstable; it could fall at any time. This single core needs support so that it will be stable. Engineers came up with an innovative solution similar to the way dam’s stand strong - The buttresses. You must have seen these buttresses supporting the dam wall against water pressure. Similar buttresses support hexagonal core of Burj Khalifa. We know buildings are always vertical, they are never inclined, right? To make the towers around the buttresses practical, they infused a stepped shape design to the buttresses.

Fig 2a : buttresses support hexagonal core

Here is the main twist. The engineers designed the buttresses so that you can actually live next to them without even realizing they are buttresses. The architects of the Burj Khalifa also efficiently used this space for corridors, so from the lift, people walk to their flats between the buttress walls as shown in fig 2b.

Fig 2b : Interwined structural plus architectural design

The architects designed huge glass facades around the buttresses, giving all the hotels and living spaces inside the facades a breath-taking view from all sides. The support needed for these glass facades came from these cross walls and columns as shown below.

Fig 2c : Crosswall and columns

How does Burj Khalifa resist storms

The main function of the cross wall is not to support the facades. To understand it let’s check out an example. Suppose there’s a sandstorm in Dubai, and there are no cross walls. Consider the situation. As shown on the right side of fig 3 the forces come through buttresses on its opposite side. The forces of resistance coming from the buttresses on the opposite side save the building from toppling over. On the left side image, the force of the wind is resisted by the combined effect of both these buttresses, which are at an angle. If the storm direction as shown in the right side of the image, the butteresses 180 degree to it. resist it

Fig 3 : Burj Khalifa overcoming wind force

However, such a slender building and a huge force from the heavy sandstorm will obviously lead to the whole building structure bending too much. We need to reduce this bending and make our burj khalifa more flexible.

Burj Khalifa can bent 6 feet !

We knew that concrete is weak against tensile stress. Concrete can only withstand a small amount of tensile stress, if the tensile stress continues to increase the concrete will crack easily (refer fig 4a). Even with the presence of steel bars in the RCC, with heavy wind speed the Burj khalifa can have good damages. So we need a prevention method. (refer fig 4b).

Fig 4a : Tensile stress break the concrete block
Fig 4b : Steel bar inside hexagonal bars

The best method to prevent a cantilever beam bending in structural engineering is by using an I-shaped section. That’s exactly what we’re doing when we connect the cross walls to the buttresses. Observe the below image carefully you can see the shape has now become like an I cross-section. The entire building is now structurally strong and can withstand the tensile stress without bending.

Fig 5: I-shaped section

The interesting thing is that around 70% of the Burj Khalifa is supported by the concrete core. The top 25% does not have any concrete core support. It is a steel structure. The Burj Khalifa mainly resists bending, but the top of this superstructure is allowed to bend and sway by about six feet in windy storms as shown in fig 6. The steel can easily resist tensile loads.

Fig 6 : Top section is bending due to wind resist

Interesting fact about Burj Khalifa - Mechanical floors

Let me show you an amazing fact. Can you see some black stripes on the original Burj Khalifa design?(refer fig 7b). They're mechanical floors. Look at this weblike structure of columns of the entire burj khalifa(refer fig 7a). We need to interconnect them together for structural integrity. This is done at the mechanical floors by connecting them together with walls, beams etc.

Fig 7a : Weblink structure of burj khalifa

The mechanical roofs are also used to house electrical and air refrigeration systems, water tanks and many other systems that bring the Burj Khalifa to life. Nobody stays on those roofs. These floors have a different appearance because they use pipes which are used by the workers so they can grip onto them when cleaning the glass facade(refer fig 7c).

Fig 7b : Black stripe on Burj Khalifa
Fig 7c: Mechanical floors

That's all in this article. I hope you enjoyed structural analysis and some interesting facts about Burj Khalifa. I will explain in the next part how this wonderful structure was created.

Thanks for reading!