The Burj Khalifa is a mixed-use development tower that stands at a height of 828 meters and has a total of 163 floors. It comprises residential, hotel, commercial, office, entertainment, shopping, and leisure establishments, with a total floor area of 460,000 square meters. The tower’s design was inspired by the geometry of the indigenous desert flower of Saudi Arabia, and the design patterns embody Islamic architecture. The tower has a central core with three wings, and each wing consists of four bays, with one outer bay peeling away on every seventh floor as the structure spirals upward.
To maximize the view and provide tenants with ample natural light, the tower’s designers opted for a Y-shaped floor plan instead of the traditional multi-layered floor plates. The Y-shaped plan also helps to reduce the impact of wind load on the building. Additionally, the tower has a podium around its base and four to six stories of underground parking garage. The foundation of the tower consists of a 3.7-meter-thick raft foundation supported by bored piles that are 1.5 meters in diameter and extend 50 meters below the base of the foundation.
Figure-1: Burj Khalifa Tower
The most significant challenges faced during the design of the Burj Khalifa were in developing a cost-effective foundation design to resist wind load and support the tower’s weight in poor soil and rock conditions. This article discusses the structural and geotechnical features of the tower, including the geology of the area, foundation design, construction process, and pile load testing program.
1. Location of the Burj Khalifa
The Burj Khalifa Tower, situated in Dubai, United Arab Emirates, was made available for public access in January 2010. This towering structure is one of the most remarkable and recognizable buildings in the world, and is widely regarded as an engineering marvel.
Located in the bustling city of Dubai, the Burj Khalifa Tower stands tall and proud, towering above the surrounding landscape. The tower’s impressive height and unique design make it a popular destination for tourists and visitors from all over the world.
Since its opening, the Burj Khalifa Tower has become an iconic symbol of modern architecture and engineering. The building’s construction was a feat of human ingenuity, and it continues to inspire and impress people from all walks of life. The tower’s location in Dubai, a city known for its innovation and ambition, only adds to its allure and prestige.
2. Geology of the Burj Khalifa Site
The Burj Khalifa site has a complex subsurface profile consisting of horizontally stratified deposits that are highly variable due to the nature of deposition and the hot-dry weather conditions. The subsurface profile comprises medium-thick to extremely loose granular silty sands at a depth of a few meters below the base, with a thickness of 4 m. The silty sands are underlain by an interbedded layer of weak sandstone, cemented sand, siltstone, and conglomerate with a thickness of 70 m. Groundwater levels are typically high throughout the location, with the groundwater table at around 2.5 m below ground level during excavations.
The unconfined compressive strength of the granular silty sand is approximately 2 to 3 MPa, while that of the sandstone layer is around 1 to 3 MPa. The geotechnical analysis revealed that the subsurface profile has the potential to lose its stiffness under cyclic earthquake loading. However, the installation of piles has increased the stiffness capacity of soil-pile interaction material enough to resist cyclic earthquake loading.
3. Structural System
The superstructure of the Burj Khalifa Tower is composed of two primary components: the lateral load resisting system and the floor framing system. The tower, being the tallest in the world, requires a robust and sturdy structure to withstand any potential lateral forces such as wind and earthquakes. The lateral load resisting system is responsible for this critical function.
On the other hand, the floor framing system provides support and stability for the tower’s various floors. The tower has a total of 163 floors, and each floor needs to be built with sufficient strength to support the weight of the building and its occupants. The floor framing system is specifically designed to provide the necessary strength and support to ensure the stability of the entire structure.
Together, these two systems make up the foundation of the Burj Khalifa Tower’s superstructure. The combination of the lateral load resisting system and the floor framing system ensures the tower’s structural integrity and stability. It is a testament to the ingenuity and expertise of the engineers and architects who designed and built the tower, making it an iconic landmark in the modern world.
3.1 Lateral Load Resisting System
The Burj Khalifa Tower’s lateral load resisting system comprises ductile core walls made of high-performance reinforced concrete, which are connected to reinforced concrete shear wall panels that, in turn, connect to the exterior reinforced concrete columns. The thickness of the core wall varies between 1300 mm to 500 mm.
Composite beams of reinforced concrete are used to connect the core walls of the tower, with a thickness ranging between 800 mm to 1100 mm. However, at some locations, the composite beams could not be provided due to depth limitations. In such cases, built steel beams were used instead.
To maintain consistency, the width of both composite and steel beams was matched to the width of the adjacent core wall. Finally, a tall spire was added to the top of the core wall to make the Burj Khalifa Tower the world’s tallest tower in all categories.
3.2 Floor Framing System
The floor framing system of the Burj Khalifa Tower includes two-way reinforced concrete flat slabs for both hotel and residential floors. The thickness of the slab for the flooring system varies between 200 mm to 300 mm. The spacing of slabs is 9 m between the interior core wall and exterior columns. At the tip of the tower, two-way reinforced concrete flat slabs with a thickness of 225 mm to 250 mm are provided.
To enhance the lateral resistance within the interior core, a flat slab with beams was installed. This particular design feature provides additional support and stability to the tower’s structure. Overall, the floor framing system of the Burj Khalifa Tower is engineered to ensure the tower’s stability and safety, allowing it to withstand the high winds and seismic activity common in its location.
4. Foundation System
The foundation design of the Burj Khalifa Tower, the world’s tallest structure, involved the use of pile foundation to resist both vertical and lateral loads. A 3.7 m thick raft was placed on top of 194 high-performance reinforced concrete bored piles with a diameter of 1.5 m. The piles were extended 50 m below the base of the raft. The podium was established on a 0.65 m thick raft supported by 750 bored piles with a diameter of 0.9 m, extending 35 m below the base of the raft. The raft foundation was constructed using high-performance self-compacting concrete (SCC) with a minimum 100 mm blinding slab as a waterproofing membrane.
Polymer drilling fluid was used instead of the conventional bentonite drilling fluid for constructing the pile foundation, as it proved to be more effective in enhancing the workability of the piles. The corners of the piles experienced a maximum load of 35 MN, while the center of the piles had a minimum load of 12-13 MN. A factor of safety of 2 was adopted for both lateral and vertical loads on the pile group to restrict the lateral movement of the pile block. Waterproofing members were provided at the bottom and sides of the raft foundation to protect it from water ingress.
The Tremie method was used for continuous pouring of concrete for piles, and a 0.30 ratio of water to cement (w/c) was adopted for SCC. A robust cathodic protection system was developed to protect the foundation system of Burj Khalifa Tower from chloride and sulfate attack from the soil at the site.
The presence of marine deposit and silty sand soil up to 3.5 m from the ground surface increased the possibility of liquefaction during seismic events. Therefore, a liquefaction assessment was carried out, and the pile foundation was placed below the level of marine deposit and silty sand soil to ensure its safety. The raft foundation bottom and all sides were protected with a waterproofing membrane.
4.1 Pile load Testing Program
The pile load testing program involved two stages. In the first stage, seven trail piles were loaded before the foundation construction, while in the second stage, the eight working piles were loaded during the foundation construction. Additionally, ten piles were chosen for dynamic pile load testing, and a sonic integrity test was conducted to assess the vertical and lateral capacity of the piles during foundation construction.
The primary objective of the pile load testing program was to develop a load-settlement response curve for the piles and validate design assumptions. Various factors were studied during the pile load tests, including the effects of pile shaft length, shaft grouting, shaft diameter, uplift (tension) loading, lateral loading, and cyclic loading.
Figure-6: Static pile load test setup
The results of pile load testing indicate that the tower is safe against bearing capacity failure, with a factor of safety of more than three at the working load. This provides a comfortable margin of safety. Additionally, the point load capacity of the piles exceeded the ultimate axial load capacity. However, the skin friction capacity of the piles was fully mobilized above 30 m, despite significant capacity available below 30 m.
The maximum settlement observed for individual piles was well below the limit at 70 mm, indicating minimal settlement concerns. Furthermore, the effect of shaft grouting was found to increase the skin friction capacity of the piles, further enhancing their performance.
The stiffness values under cyclic and lateral loading were found to be very high, providing an excellent margin of safety against potential deformations. However, the factor of safety against uplift was only 2, which influenced the compressive capacity of the piles due to uplift pressure. This suggests that uplift considerations should be taken into account in the design and construction of the piles to ensure adequate performance in uplift conditions.
5. Construction of Burj Khalifa Tower
The tower construction project began with the completion of pile and raft foundation works by February 2005. This was followed by the commencement of the superstructure construction in April 2005, with the tower being fully constructed to its desired position in January 2009.
To ensure the timely completion of the project, several technologies and strategies were implemented. One such approach was the adoption of a unique 3-day cycle for structural works. This enabled the construction team to complete the necessary structural work within a short period.
Additionally, a transportation system with a large capacity of equipment and optimum building materials was put in place. This helped to ensure that the required materials were readily available, thereby reducing delays in the construction process.
To meet the requirements of the tower construction, an optimum formwork system was provided. This system was designed to cater to the height of the tower and ensure that the necessary formwork was in place during the construction process.
Logistic plans were also developed during the course of tower construction. These plans helped to ensure that the necessary materials and equipment were delivered to the construction site in a timely manner, thereby reducing any potential delays in the construction process.
5.1 Planning for the Concrete Work
The construction of the Burj Khalifa Tower prioritized concrete testing and quality programs, which were initiated early on during the development of mix design criteria and continued throughout the entire construction process. Several testing regimes were implemented to ensure the quality of the concrete used in the tower.
Mechanical properties of the concrete, such as modulus of elasticity, tensile strength, and compressive strength, were carefully calculated and monitored. Durability tests, including initial and 30-minute surface absorption tests, were conducted to assess the resistance of the concrete to deterioration over time.
Creep and shrinkage tests were set up for different types of concrete mix designs to evaluate their behavior under load and environmental conditions. Permeability tests, such as rapid chloride tests, were performed to measure the resistance of the concrete to penetration of chloride ions that can cause corrosion.
Heat of hydration tests were carried out, which involved cube analysis and full-scale setups to measure the effect of heat generated during the curing process on large-sized concrete elements with dimensions greater than 1.0 m.
Pump simulation tests were also conducted to ensure that the concrete used in the tower could be pumped to large distances without any issues, ensuring its pumpability and workability during the construction process.
Overall, a comprehensive concrete testing and quality program was implemented for the construction of the Burj Khalifa Tower to ensure the durability, performance, and safety of the concrete used in this iconic skyscraper.
Figure-8: Heat of hydration test
Various tests were carried out to validate the construction sequence of the large-sized elements and to formulate effective curing plans. These tests took into account the fluctuations in daily and seasonal temperatures. The purpose of these tests was to ensure that the construction process was executed in the correct order and that the curing plans were designed to accommodate the temperature changes that could occur on a daily or seasonal basis. By conducting these tests, the construction team aimed to optimize the construction process and ensure that the large-sized elements were cured properly, taking into account the temperature variations that could affect the quality and durability of the final structure.
5.2 Technologies Used to Achieve 3-Day Cycle
A tower of significant size needed to be built within a tight schedule. To achieve this, a 3-day cycle program was developed for the concrete work. The construction technologies used for the program included the Auto Climbing formwork system (ACS), which was utilized for construction at greater heights. This system allowed for a smoother construction process, resulting in faster progress.
High-performance concrete was used to meet the tower’s high durability requirements, as well as its need for high modulus, high strength, and pumping requirements. Using this type of concrete allowed for a more efficient construction process.
To minimize labor requirements, a simple drop head formwork system was developed. This system provided a semi-automatic dismantling and assembling process of formwork, which allowed for a faster construction process.
Rebar pre-fabrication was also used to speed up the construction process and reduce the likelihood of human error in rebar fabrication. By utilizing this method, the project was able to move forward more quickly and efficiently.
FAQs
What is the type of foundation of the Burj Khalifa Tower?
The tower’s construction involved the use of both raft and pile foundation. The foundation of the tower is comprised of a 3.7-meter-thick raft, which is supported by 194 bored piles. This type of foundation is often used in construction to distribute the weight of the structure evenly over a larger area, reducing the risk of settling or instability. The use of a raft foundation provides a stable base for the tower, while the piles add additional support and help to anchor the foundation to the ground. This type of foundation is particularly useful in areas with unstable soil or where the structure being built is particularly heavy. With the combination of a raft and pile foundation, the tower can be built with confidence, knowing that it will be supported by a strong and stable foundation.
What is the grade of concrete used in the construction of the Burj Khalifa Tower?
The Burj Khalifa Tower was constructed using concrete made from fly ash with a grade ranging from M-60 to M-80.
What is the height of the Burj Khalifa Tower?
The Burj Khalifa Tower, standing at a height of 828 meters from the ground level, holds the title of the world’s tallest structure.
How many floors are there in the Burj Khalifa Tower?
There isn’t much context to work with, but I will do my best to provide some additional information based on the given sentence.
The sentence states that there is a tower consisting of 160 floors. We don’t know much else about the tower, such as its location, purpose, or design. However, we can assume that a tower with 160 floors is quite tall, likely among the tallest buildings in the world. It may be a skyscraper in a major city, serving as a commercial or residential space.
The construction of such a tall building would require significant resources and engineering expertise, and it would need to adhere to strict safety codes and regulations. It may have taken years to design and build, involving thousands of workers and a vast array of specialized equipment and materials.
A tower of this size would likely have many elevators and staircases to facilitate movement throughout the building. It may also have a variety of amenities and services for occupants, such as restaurants, shops, and recreational facilities. Depending on its location, it could offer stunning views of the surrounding area and be a major tourist attraction.
In summary, the sentence “The tower consists of 160 floors” tells us that there is a very tall building with many levels, but we don’t know much else about it. However, we can imagine that constructing and maintaining such a building would be a significant undertaking, and it could have many different uses and features depending on its location and purpose.
What is the total construction cost of the Burj Khalifa Tower?
The construction project incurred a total cost of USD 1.5 billion.