Biography: Sina Yasha is a current student of USC School of Architecture for bachelor’s degree.
Will be graduating in 2015. His interests center primarily around sustainable cities and infrastructure.
Keywords: High Rise, Architecture, Construction, Building, Tall, Floor plan, Wind.
Suggested Multimedia: Burj Khalifa (Burj Dubai) Construction - Animation http://www.youtube.com/watch?v=yNfpwdLVZ4c
Abstract: From the Great Pyramids of Giza of the old world to the Taipei 101 building in Taipei which previously held the title of world’s tallest building, mankind had always had a fascination for tall edifices. From the old world king The Great Pyramid of Giza to the newly crowned world’s tallest Burj Khalifa in Dubai, we have always had looked with interest and pondered how did these magnificent structures came to be. With recent advancements in engineering and design building taller skyscrapers has now become not only possible but may become the trend of the future given the limited land space we have in the world. The construction of the world’s tallest building might not have been possible without the advancements in design, understanding of nature and creative use of materials that it magnificently stands proof of.
Throughout history, humankind has always shown a fascination with big and tall structures. From the Great Pyramids in Giza, to the Old St. Paul’s cathedral in London, to the Eiffel tower in France people have always viewed these grand structures with awe and fascination, and at the same time wonder how these structures came to be. This fascination has led people to try to create bigger and taller structures that not only surpass the achievements of other tall edifices but also pushes the current boundaries of what engineering, architecture and even science can achieve. Like then, people who look at them question what marvels of science and engineering have made these superstructures possible. We look at what made the construction of the world’s tallest building possible.
World’s tallest building
Enter the Burj Khalifa.
In January 2004, excavation work for the Burj Khalifa building began with construction work beginning on September 21 of the same year . Initially conceptualized to be the centerpiece of a large-scale development that is centered on service and tourism, Burj Khalifa, which officially opened on January 4, 2010, achieves that and more .
Burj Khalifa holds a number of records upon its completion. It is the world’s tallest building according to the Council on Tall Buildings and Urban Habitat, which stands as the arbiter of the criteria for which the world’s tallest building is chosen . Burj Khalifa has a height of 828 meters, 167 floors with concrete and steel as the main materials of construction . The building also holds other records other than being the tallest building in the world. It holds the record for being the tallest freestanding structure in the world, the highest number of stories in the world including the highest occupied floor in the world. In addition, Burj Khalifa also holds the world record for having the highest outdoor observation deck in the world, the longest elevator travel distance and the tallest service elevator in the world . The building also holds the unofficial records for the highest installation of an aluminum and glass façade, at a height of 512 meters. The Burj Khalifa also holds the record for highest concrete pumping record when construction pumped concrete for the buildings concrete corewalls in November 2007 at a height of 601 meters. Burj Khalifa is more than world records though as what is equally as amazing as its records are the things that made the construction of this fascinating and record holding edifice possible .
The Buttressed Core
Burj Khalifa uses the buttressed core system, a tripod-shaped design which features all three wings supporting each other. The engineering firm Skidmore, Owings, and Merrill, first developed this. Figure 1 below shows the Y-shaped buttressed core used in Burj Khalifa compared to other buildings.
Figure 1 shows cross sections of the foundation and floor plans of Burj Khalifa compared to other buildings. Source: http://en.wikipedia.org/wiki/File:Comparisonfinal001fx7.png
The Y - Shaped Buttressed Core. Source: http://www.gostructural.com/print-magazinearticle-design_and_construction_of_the-7709.html
he biggest key in building the Burj Khalifa and possibly in building even taller towers is the buttressed core system. This design is a kind of three-pronged spear that allows stability, viably usable space and limited loss of space for structural elements .
First developed by the architectural and engineering firm Skidmore, Owings, and Merrill, the buttressed core is seen by many architects as the answer to the question of what would best be used in the building of “supertall” structures (SOM) . The buttressed core structural system is characterized by its tripod-shaped design, which features a sturdy central core that in turn is surrounded by three building wings. In this system, the wings are co-dependent and each is supported or buttressed by the other two. This core is comprised of a six-sided centerpiece, which provides torsional resistance and prevents twisting of the tower. As buildings get taller, their tendency to twist about their vertical axis increases. The buttressed core solves this problem by using the three wings of the building to support the center core, with the center core in turn allowing the wings to be supported by each other . Engineers say that without the use of the buttressed core system, Burj Khalifa will not have been constructed as it is now. However, it is possible for a building as tall as Burj Khalifa to be built without the buttressed core system, there are more things that are to be considered without it. Typically, buildings built without the advantages of the buttressed core system lose more space to engineering structures compared to one that uses the buttressed core. By using the buttressed core inherent characteristic of one-wing supporting the other two, there is not as much need to build structural items that will support the building. The addition of these structural items takes up space in building not using the buttressed core that can otherwise be used for other means. (See Fig. 2 below)
Figure 2. Illustration by: Peter Bollinger from Wired magazine
Taming the Forces of Nature
The construction of the world’s tallest building comes with it numerous issues when it comes to its design and construction. Not only must architects and engineers consider the answers to the questions of the buildings designs they also have a multitude of concerns to think about and solve. Different engineers of different disciplines (i.e. structural engineers, mechanical engineers, electrical engineers) need to be able address issues within their area and at the same time be able to work together in order to achieve efficient solutions. For example, in construction, prior to pouring concrete on some parts of the floor, plumbing engineers and electrical engineers, would have to ensure that they have already installed the parts that they are responsible for. In addition to installing it, they should be able to test that what they have installed will work or make arrangements to be able to test them later without having to destroy the poured concrete, which by that time would have already settled and have been cured. Aside from this, questions as the use of resources and the materials should also be meticulously checked and rechecked to ensure that they meet the requirements of the building. In the undertaking of how to build the world’s tallest building these questions though seem to be on the easier side of the deal, they are after all controllable. The harder issue is how to solve potential problems brought about by the effects of nature.
The biggest issue that builders of the Burj Khalifa faced in the design and construction is the wind effect. After their initial testing of their design using wind tunnels, they found out that their design was not representative of the vision that they had and failed their expectations . Engineers and architects then worked on changing their model and worked towards tuning their design to be able to “confuse” the effects of the wind on the building so that its forces would stay manageable, and its effects would not be compounded . They also used the forces of gravity on the building to help stabilize the structure and resist the wind forces . The Y shaped design of the building is akin to spreading one’s feet to have a wider base where gravity can act. The resulting wider base then allows you to use your own weight to keep from toppling over . The resulting reduced forces resulted in their ability to build much higher than they previously thought they could.
In addition, the builders also considered the orientation of the building to lessen the effects of the wind. Knowing that the most frequent direction of the strong winds in Dubai come from the northwest, south and east, they positioned the buildings wings pointing to where the strong winds come from to lessen their effects . This also helped in the builders’ goal of “confusing” the wind to lessen its shear effects and its drag on the building. (see Figure 3)
Figure 3. Shown here is wind effect on Burj Khalifa on the lower, middle and upper floors. The Y shaped design breaks the wind pattern and lessens the damaging effect of the wind. Source: http://www.dubai-forever.com/images/burj-khalifa-wind.jpg
High Performance Concrete
As anyone with even the smallest knowledge of construction know, the materials that may prove effective in constructing a small building does not make it necessarily usable on a building of greater scale. The kind of wood that works for a 2 story home for example may not be strong enough to support the loads of a 4 story house. Factors like the wood’s density and even the composition of the wood itself need to be considered. This too was an essential issue that needed to be addressed in building the world’s tallest building which was almost entirely made up of steel and concrete. Burj Khalifa not only posed issues with regards to what type of concrete would the builders use but it also posed logistical issues of how to pump the concrete into the structures unprecedented heights.
The use of high-performance concrete is crucial to the structural and economic viability of building the world’s tallest skyscraper . Building even in half the scale of Burj Khalifa moves laterally and the effect of the building height create vertical forces that may collapse the building due to its own weight. The use of high-performance concrete, which has a stiffness that allows the limiting of the buildings movement and strength that allows the building to successfully oppose vertical forces, is critical. This type of concrete too has a durability that ensures the service life of the building especially in a hot, chemically aggressive environment typical of Middle East climate .
The suitability of reinforced-concrete construction is entirely dependent on the ability to pump the concrete . One of the things that needed to be overcome was question of concrete mixture. Aggregates that are used in the concrete mixture – both coarse and fine aggregate – have different abrasion characteristics. This means that different type of aggregates have different levels of how they wear or scrape at the material that they are poured into. As concrete is pumped through a pipeline, they wear away at the material that the pipeline is made of. Therefore, the effect of the type of concrete in the lifespan of the pipeline was an important thing that builders had to constantly consider. In finding a solution, the builders of Burj Khalifa had to conduct 5 separate trials using different concrete mixtures . Due to the hot climate in the Middle East the concrete mixture tended not only to dry faster even while pumping but also contributed to problems while they are pumped in the pipeline. For the Burj Khalifa project, this meant that most of the pumping done had to happen at night when temperatures were much colder. When this was possible especially with consideration to keeping up with the construction schedule, flake ice, which was then melted, was added to the mixture to provide lubrication instead of water . The concrete was also constantly tested as different levels of the building had different temperature due to its height. The builders also used three separate concrete pumps to allow for simultaneous pumping to three separate locations. At the same time that these aspects are considered, the builders also had to ensure that blockage in the concrete pipelines was not going to happen. Blockage can be caused by priming with a wet slurry, excessive delay, inadequate retardation and incompatibility of admixtures. Constant check of the concrete’s qualities was therefore done to ensure their integrity. The delivery of the mixed concrete, which is mixed in batching plants and then delivered by trucks were also timed to ensure that the concrete that is being pumped is as fresh as possible .
Even with the excellent design and enormous effort by all involved parties in the construction of Burj Khalifa, the project would have been impossible without the effective use of high-performance concrete.
As the world moves toward the construction of buildings in much greater scales than ever before it is important for builders and for the public to understand what goes into the construction of such buildings. Engineers and architects continuously aim to make statements that prove the achievement of advances in technology and understanding of the factors that need to be considered in constructing super-tall buildings. Burj Khalifa stands not only as a monument to these advances but also as a monument that proves mankind’s capability to wield previously un-wieldable information and skills that leads us to be able to take big leaps forwards not only in areas of engineering but in other scientific areas as well.
Burj Khalifa is the realization of a dream that is shared by people from everywhere and from all walks of life. It is both a statement and a testament to our mankind’s ability to not only live within what nature allows but to also thrive in it. Science tells us that man is separated from other species in how we understand things and of what we think ourselves to be. Burj Khalifa is our statement. He is an amazing and marvelous declaration that tells of how we are and of what we are capable of. It is the current representation of mankind’s ability to reach for their dreams and achieve the impossible - at least until the Sky City Tower in Shanghai can get a couple of words in .
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