Overview
The Burj Khalifa boasts the accolade as the tallest structure in the world (Baker, 2009). The construction of this building surpassed several construction records that had been set by previous record holder skyscrapers. The recording-holding height is not the only interesting aspect of the structure. The construction of the building took six years. The construction of the building required the input of more than thirty contracting companies and over twelve thousand workers drawn from over one hundred countries. A construction project of this magnitude is faced with various challenges (Baker, 2009). In additional, sound geotechnical, structural, and economic aspects are required to ensure the integrity of the building and also its economic viability. The completion of the structure was attributed to among other factors the design choices made, the project management elements, and the economic aspects of the construction and the location. This paper explores these three aspects with the aim of making recommendations or design changes that could have reduced the cost of construction of the building.
Design Aspects of the Burj Khalifa
The shape of the building is triple-lobed, a design choice that borrows from the shape of the Hymenocallis flower as show in Figure 1 below. The laying of the foundation for the triple-lobed structure required some geotechnical innovations because of the nature of the soil on the construction site. The foundation for the building consists of a raft construction that has a thickness of 3.7 meters. This raft is supported by 192 bored piles that are sunk into the ground (Burj Khalifa, n.d). The dimensions of the piles vary from one place in the construction site to another depending on the soil structure. However, the average diameter of the piles is 1.5 meters and a length of 50 meters for the tower (Burj Khalifa, n.d). The length of the piles for the surrounding structures was 30 meters. This design choice was to ensure that the weight of the tower and the surrounding structures was evenly distributed on the weak sands that characterized the construction site.
Figure 1 showing the shape of the building
Source (Baker, 2009).
One of the resounding structural aspects of the building is its height. The Burj Khalifa has a height of 828 meters. One hundred and sixty-two floors are spread over this height. A building of this height comes with concerns regarding the wind loading and the effects on the structural integrity. The design choices made to overcome the potential wind loading effects include the ‘Y’ shape of the core of the structure (Burj Khalifa, n.d., Structural aspects). The ‘Y’ shape reduced the amount of force exerted by the wind on the building. The ‘Y’ shape used by the designers also proved to be ideal for the general purpose of the building (Burj Khalifa, n.d., Structural aspects).
More specifically, it was appropriate for the residential purpose because it gave an open space and ensured that the various units are not overlooking others. The shape chosen by the designers also added the stiffness of the building, an element that is important for wind performance. The central core of the ‘Y’ shape was a hexagonal structure that offered resistance to torsional movement in the event of the wind (Burj Khalifa, n.d., Structural aspects). This was achieved by constructing walls that had a thickness of between 0.5 meters and 1.3 meters. The walls that extended outwards from the hexagonal structure at the core of the building were designed to offer resistance to the moments and the shears of the wind (Burj Khalifa, n.d., Structural aspects).
The materials used in the construction of the Burj Khalifa are as extensive as the scale of the building. The concrete that was required for the construction of the building amounted to 330,000 cubic meters, with 45,000 cubic meters being used for the construction of the foundation (Burj Khalifa, n.d. Materials). The concrete was reinforced with steel rebar of 31,400 metric tons (Burj Khalifa, n.d. Materials). In addition to the concrete, the other construction material used in the large quantities was aluminum, silicone, and glass. These are the materials used to make the curtain all façade of the building (Burj Khalifa, n.d. Materials). Due to the record-breaking height of the building, the surface area of the curtain wall façade was 132,000 square meters. To cover this area, 24,000 glass panels were used on the outer perimeter of the building envelope (Burj Khalifa, n.d. Materials).
Economic Implications of the Design Aspects
The sheer size of the construction project and the structural, geotechnical, and the amount of materials used in the construction of the Burj Khalifa push the boundaries of the economies of skyscrapers. Various aspects of the design of the building had an impact on the cost of construction. As highlighted above, the size of the building scaled up every other aspect. For instance, high compressive strength is required for a building of the size to ensure that the foundation of the building can handle the enormous weight of the building. This required the use of uniquely constituted reinforced concrete. The amount of steel that was used to reinforce the concrete in the foundation was enormous (Burj Khalifa, n.d. Materials). The principle in play here is that more construction materials were required because of the size of the building. This comes at an increased cost.
The other design aspect of the building that that contributed to the increased cost of the construction is the height of the structure. It is given that the increased height of the building required more materials compared to a building of lesser height. However, the point highlighted in this argument is one of the logistics and the equipment required to hoist the construction materials to the highest points of the building. The concrete required for the highest floors was pumped upwards to 601 meters (Burj Khalifa. n.d. Materials). The enormity of this scale meant that high pumping pressures of almost two hundred bars. The economic implication of these requirements is that bigger equipment capable of generating the required pressure was needed. This means that the cost of acquiring the equipment was higher compared to a building of lesser height.
The design of the building envelope was conceived to help in ensuring the energy efficiency of the building. In this respect, the designers of the building conceptualized the use of a curtain wall façade system made of reflective glazing of a high-performance grade to reduce the solar gains from the outside (Burj Khalifa. n.d. Materials). The entire building envelope of the Burj Khalifa is covered with the curtain wall façade system. Due to the shape and height of the tower superstructure, the surface area to be covered with the curtain wall glass façade was 132,000 square meters. This translated to more than 24,000 glass panels of the reflective glazing specification to cover the entire building envelope (Burj Khalifa. n.d. Materials). This contributed to the cost of construction because a building with a shorter height would have required lesser glass panels because of a smaller surface area compared to Burj Khalifa.
The labor is one of the factors that contributed to the final construction cost of a building. Even with the automation of various processes in a construction project, big construction projects will always require a large labor force. This is more the case when the project is to be completed within a short time frame. As highlighted by Baker (2009) more than twelve thousand workers were required for this construction project. In addition, over thirty contracting companies operated at the construction site throughout the construction period. The enormity of this operation amplifies the project management scale.
A large number of workers working onsite translates to a large wage bill compared to a smaller building if all other factors remained constant. The project management and logistical operations required are also in the scale of the size of the building which further translates to a financial premium. All these factors lay testament to the economic implications that the design aspects of the buildings had on the construction of the building. The financial scales of skyscraper construction were amplified to reflect the size, shape, and the aesthetics of the building.
Design Changes to Reduce the Cost of Construction
The cost of construction for the building could be reduced with the implementation of various changes in the design aspects.
Removal of the Stepping Setbacks
The building envelope of Burj Khalifa is characterized by stepping setbacks (Baker & Pawlikowski, 2015, p.393). While some jurisdictions make the use of stepping setbacks mandatory in order to allow the penetration of more light in the streets below, setbacks are also used to achieve an aesthetic value in a building. The additional bays and surfaces in the building attributable to the setbacks result in an increase in the construction material. The recommendation entails the removal of the many stepping setbacks and in its place a tapered tower is to be constructed (Baker & Pawlikowski, 2015, p.393). In addition to the reduction of the construction material, this recommendation also eliminates the need to organize the vortices of the building to respond to the forces of wind as the building narrows as the height increases. This also helps reduce the cost of construction because it reduces the amount of reinforcement required to strengthen the building against the moments and sheer of the wind. This recommendation also ensures a smooth gravity load (Baker & Pawlikowski, 2015, p.393).
The Removal of the Outrigger Zone
This recommendation reduces the cost of construction by reducing the amount of time required in constructing one floor. The design of Burj Khalifa features perimeter walls that are designed to depend on an outrigger system to fasten them to the core structure of the building (Baker & Pawlikowski, 2015, p.393). The outriggers are strongly reinforced with concrete and steel to enable them to link the perimeter walls of the building to the hexagonal structure at the core of the building (Baker & Pawlikowski, 2015, p.393). The construction of the outriggers requires more time compared to the constriction of the perimeter walls and the adjoining floors. However, the fact that the perimeter walls and the adjoining floors cannot be construction before the outrigger is constructed and heals means that more time is taken in the construction process. Baker & Pawlikowski (2015, p.393) found that the floor cycle for a typical floor in the building required 2.5 days. However, the outrigger system resulted in an increase in the number of days taken.
The Incorporation of the Buttressed Core Concept
The buttressed core concept helps reduce the cost of construction by reducing the materials required and also saving time in the construction process. The buttressed core concept eliminates the need for perimeter walls in the building. This would have significantly reduced the number of construction materials and also the time required to construct those walls (Baker & Pawlikowski, 2015, p.393). In the place of the perimeter wall, the design features cantilever framings that are made of reinforced concrete. It is from these framings that the plates that comprise the floors of the build are placed. The implementation of this recommendation also results in the removal of the outriggers in the previous design (Baker & Pawlikowski, 2015, p.393). The removal of these elements results in a reduction in the construction materials and the time required for the construction.
The Use of the Broad Sustainable Building Prefabricated Construction
The application of this recommendation reduces the cost of construction by significantly reducing the time required for the construction and minimizing waste. The reduction of the waste is achieved by the use of modular design (Council on Tall Buildings and Urban Habitat, 2013). This concept utilizes prefabricated steel frame structures. These structures can be fabricated in the factories and then ferried to the construction site for installation. The amount of construction waste produced through the use of this design is comparable to 1% of the wastes produced through a conventional construction process of a similar building. The structural performance of the building is also admirable considering that the stress distribution is even, and its structure can support high bearing capacities Council on Tall Buildings and Urban Habitat, 2013).
Reduction of the External Bays
Figure 1 shows that that each of the lobes has four bays. The reduction in the number of bays will help reduce the cost of construction by way of reducing the number of materials to construct the external walls as well as the labor requirements (Dupr, 2013, p.21).
References
Baker, B. and Pawlikowski, J. 2015. The Design and Construction of the World’s Tallest Building: The Burj Khalifa, Dubai. [PDF]. Available at :< http://www.iabse.org/Images/Publications_PDF/SEI/SEI.Burj%20Dubai.pdf> [Accessed 8 April 2016].
Baker, W. 2009. Design and construction of the world’s tallest building: The Burj Dubai. [Online]. Available at :< http://cenews.com/article/7709/design_and_construction_of_the _world_acute_s_tallest_building__the_burj_dubai> [Accessed 8 April 2016].
Burj Khalifa. (n.d). Geotechnical aspects. [Online]. Available at :< https://sites.google.com/site/burjkhalifatower/documents> [Accessed 8 April 2016].
Burj Khalifa. (n.d). Materials. [Online]. Available at :< https://sites.google.com/site/burjkhalifatower/documents> [Accessed 8 April 2016].
Burj Khalifa. (n.d). Structural aspects. [Online]. Available at :< https://sites.google.com/site/burjkhalifatower/documents> [Accessed 8 April 2016].
Council on Tall Buildings and Urban Habitat. 2013. BSB Prefabricated Construction Method, Changsha. [Online]. Available at :< http://www.ctbuh.org/TallBuildings/ FeaturedTallBuildings/FeaturedTallBuildingArchive2013/BSBPrefabricatedConstruction MethodChangsha/tabid/6067/language/en-US/Default.aspx> [Accessed 8 April 2016].
Dupr, J. 2013. Skyscrapers: A History of the World's Most Extraordinary Buildings. New York: Hachette Books
