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The Burj Khalifa is the tallest structure in the world at 828 meters and a total of 163 floors. Famous as a mixed-use development tower with a total area of 460,000 m2, includes residential, hotel, commercial, office, entertainment, shopping and leisure establishments.
The idea behind the design of the Burj Khalifa originated from the flower geometry indigenous to the desert of Saudi Arabia, while the tower's design patterns symbolize Islamic architecture. The tower is built around a central core with three wings, each wing comprising four spans. On every seventh floor, an exterior bay opens up as the structure spirals into the sky.
Unlike many tall towers with multi-layer floorboards, a Y-shaped floor plan was adopted for the Burj Khalifa to extend the view and provide occupants with plenty of natural light. Furthermore, the Y-shaped plan was considered to reduce the effect of wind load on the building.
In addition, it has a podium around the base of the structure. It also includes four to six floors of underground parking. The tower is built on a 3.7 m thick raft base and supported by drilled piles. The piles are 1.5 m in diameter and extend 50 m below the base of the foundation basin.
Crucial difficulties in the design of the tower were encountered in making an economical foundation design, where soil and rock conditions were poor and a substantial amount of wind loading had to be resisted.
This article discusses the structural and geotechnical features of the Burj Khalifa Tower, such as the area's geology, foundation design, construction process, and pile load testing program.
- 1. Location of the Burj Khalifa
- 2. Geology of the Burj Khalifa site
- 3. Structural System
- 3.1 Side load resistance system
- 3.2 Floor structure system
- 4. Foundation system
- 4.1 Battery Load Test Program
- 5. Construction of the Burj Khalifa Tower
- 5.1 Planning of the concrete work
- 5.2 Technologies used to achieve the 3-day cycle
- 5.3 Construction sequence of the superstructure
- common questions
1. Location of the Burj Khalifa
The Burj Khalifa Tower opened to the public in January 2010. It is located in Dubai, in the United Arab Emirates. The picture below represents the location of the Burj Khalifa Tower.
2. Geology of the Burj Khalifa site
The following points describe the geology of the Burj Khalifa site:
- Soil conditions consisted of a horizontally stratified subsurface profile, extremely variable and complicated due to the nature of the deposition and common climatic conditions of heat and drought.
- Medium to extremely loose granular silty sands (marine deposits) were present a few meters below the base. The thickness of these strata is 4 m.
- Silt sands are supported by extremely weak to weak sandstones. This layer is interspersed with extremely weak cemented sand, fine-grained siltstone, and weak to reasonably weak conglomerate. The thickness of this stratum is 70 m.
- Groundwater levels were typically high throughout the site. During excavations, the water table was about 2.5 m below ground level.
- The unconfined compressive strength of the granular silty sand was about 2 to 3 MPa, and that of the sandstone layer was about 1 to 3 MPa.
- The geotechnical results showed a potential ability to destroy material stiffness under cyclic seismic loading. However, after thestack installation, the stiffness capacity of the soil-pile interaction material was sufficient to withstand the cyclic seismic load.
The side load resistance system and the floor frame system are the two main components of the superstructure of the Burj Khalifa Tower and these systems are discussed below.
3.1 Side load resistance system
The tower's lateral load-bearing system consists of high-performance reinforced concrete ductile core walls. These walls were connected to the outside.reinforced concrete columnsthrough a series of reinforced concrete shear wall panels. The following points describe the Burj Khalifa Tower's side load resistance system:
- The core wall thickness varies between 1300 mm and 500 mm.
- Reinforced concrete composite beams were used to connect the tower core walls, and these beams ranged in thickness from 800 mm to 1100 mm.
- In some locations it was not possible to supply composite beams due to depth limitations. Therefore, in these places, built steel beams were provided.
- The width of the composite beam and steel beams was given to match the width of the adjacent core wall.
- A very tall tower was provided on top of the central wall. This tower was provided to make the structure the tallest tower in the world in all categories.
3.2 Floor structure system
The following points describe the Burj Khalifa Tower floor structure system:
- Two-way reinforced concrete flat slabs were supplied for hotel and residential floors. The slab thickness for the flooring system varies between 200 mm and 300 mm.
- The spacing of the slabs was maintained at 9 m between the inner wall of the core and the outer pillars.
- On top of the tower, flat slabs of reinforced concrete from 225 mm to 250 mm thick were placed in two directions.
- However, inside the inner core, a smooth slab with beams was placed to provide greater lateral resistance.
Pile foundations were adopted to withstand the vertical and lateral loads of the world's tallest structure. The following points describe the design details of the foundation of the Burj Khalifa Tower:
- The tower is built on a 3.7 m thick raft supported by 194 high-performance reinforcements.concrete perforated piles. The diameter of the piles was 1.5 m and the piles were placed 50 m below the base of the raft.
- The podium was established on a 0.65 m thick raft supported by 750 drilled piles. The diameter of the piles is 0.9 m and the piles extend 35 m below the base of the raft.
- The reinforced concrete foundation basin was built with high-performance self-compacting concrete (SCC). A blind slab of at least 100 mm was used as a waterproofing membrane.
- Polymer drilling fluid was used to build the pile foundation. It was much more effective than conventional bentonite drilling fluid because it improved the workability of the piles beyond expectations.
- The maximum load of 35 MN was observed at the corners of the piles. In contrast, a minimum load of 12-13 MN was observed at the center of the piles.
- To restrict the lateral movement of the pile cap, a factor of safety of 2 was adopted for the lateral and vertical load on the pile group.
- Waterproofing elements were provided on the bottom and sides of the base of the raft to protect it from water ingress.
- The bottom of the raft base and all sides were protected with a waterproofing membrane.
- The Tremie method was adopted for continuous concreting for piles and for SCC the w/c ratio of 0.30 was adopted.
- To protect the foundation system of the Burj Khalifa Tower, a robust cathodic protection system was developed. This system provided security against chloride andsulfate attackdo solo no local.
- Marine deposits and silty sandy soil were present up to 3.5 m from the soil surface. Therefore, the possibility of liquefaction occurring during the seismic event was high. Therefore, a liquefaction assessment was carried out. However, the pile foundation was provided below the level of the marine deposit and silty sand ground to make it secure.
4.1Battery load test program
A static pile load test was carried out in two steps. The first consisted of loading seven piles before building the foundation. The second consisted of loading the eight work piles and was carried out during the construction of the foundation.
In addition, a total of ten piles were chosen for dynamic pile load testing. In addition, a sonic integrity test was carried out to verify the vertical and lateral capacity of the piles during the execution of the foundation.
The primary objective of the pile load test program was to develop a pile settlement load response curve and validate the design assumptions. The following factors were studied during various pile load tests:
- Effect of stack axis length
- Pit grout effect
- Shaft diameter effect
- Lifting Load Effect (Strain)
- side load effect
- Cyclic loading effect
The results of the battery load tests are summarized below:
- In the workload, the safety factor against load capacity failure was greater than three. Thus, the turret was safe by a comfortable margin against carrying capacity failure.
- The punctual load capacity of the piles was greater than the ultimate axial load capacity. However, the surface friction capacity of the piles was fully mobilized above 30 m, although significant surface friction capacity was available below 30 m.
- The maximum settlement was 70 mm for individual piles, well below the limit.
- The effect of the well grout increased thesuperficial friction capacity of piles.
- Under cyclic and lateral load, the stiffness values were very high, thus providing an excellent margin of safety.
- The uplift safety factor was 2 because the uplift pressure was influencing the compressive capacity of the piles.
5.Construction of the Burj Khalifa Tower
For the construction of the tower, pile and raft foundation work was first completed in February 2005. After that, construction of the tower superstructure began in April 2005, and its tower was fully built in the desired position in January from 2009.
The following technologies and strategies were implemented to build the tower on time:
- A unique 3-day cycle approach was adopted for structural work.
- A transport system with a large capacity of equipment and optimized construction materials was adopted.
- An ideal formwork system was provided to meet the tower construction requirements along with the height of the tower.
- Logistical plans were developed during the construction of the tower.
5.1Concrete work planning
For the successful construction of the tower, the main focus was theconcrete and quality testprogram. These programs began shortly after the mix design criteria were developed and continued through the last phase of the construction process. The following points describe the test regimes included for the construction of the Burj Khalifa Tower:
- All mechanical properties such as modulus of elasticity, tensile strength and compressive strength of the concrete were calculated.
- Durability tests were carried out. These tests included an initial and 30-minute surface absorption test.
- A setup for creep and shrinkage testing has been developed for different types of concrete mix projects.
- A permeability test, such as the rapid chloride test, was performed.
- The heat of hydration test was performed. This test consists of full-scale cube and configuration analysis to measure the effect of hydration heat on large concrete elements greater than 1.0 m in size.
- Pumping simulation tests were carried out so that the pumpability of concrete over long distances could be achieved.
In summary, all these tests were performed to confirm the construction sequence of large elements and to develop cure plans considering daily and seasonal temperature fluctuations.
5.2 Technologies used to achieve the 3-day cycle
Build the tower of such magnitude in a very tight time frame. a 3-day cycle program has been developed for specific jobs. The following points describe the construction technologies used to achieve the 3-day cycle program for concrete works:
- For the taller construction, the Auto Climbing formwork system (ACS) was used.
- High performance concrete was used to provide high durability, high modulus, high strength and pumpability requirements.
- Keeping the labor requirement as low as possible, a simple drop-head formwork system was developed to provide a semi-automated process for dismantling and erecting the formwork.
- Rebar prefabrication was used for a faster construction process and to reduce human error in rebar fabrication.
5.3 Construction sequence of the superstructure
The construction process for superstructures and ACS is shown in Figure-9. The work of the ACS was divided into three segments. The first segment included the construction of the central core wall and the second segment included the construction of the side wall. The third segment included the construction of three tower wings. The following points describe the construction sequence of the superstructure of the Burj Khalifa Tower:
- First, the master walls of the central nucleus were built, followed by the execution of the slab of the central nucleus.
- Subsequently, the sidewall was built in continuity with the construction of the flat wing slab.
- In addition, the nose columns were built along with flat slab construction in the nose area.
- In addition, the main walls of the central core were tied to the nose columns by a series of braced walls at each mechanical level.
- The braced walls were built with steel structural members because the rebar congested the connections. Therefore, to reduce construction time and obtain greater rigidity in the joints, steel structural elements were used.
What is the foundation type of the Burj Khalifa Tower?
Raft foundations and piles were used for the construction of the tower. The tower rests on a 3.7 m thick raft supported by 194 perforated piles.
What grade of concrete is used in the construction of the Burj Khalifa Tower?
M-60 to M-80 grade concrete made from fly ash was used in the construction of the Burj Khalifa tower.
How tall is the Burj Khalifa tower?
The Burj Khalifa tower is the tallest structure in the world, rising to a height of 828 m from ground level.
How many floors does the Burj Khalifa Tower have?
The tower consists of 160 floors.
What is the total cost of building the Burj Khalifa Tower?
The total construction cost was US$1.5 billion.
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