Skyscrapers are a product of the industrial revolution, which began in England in the eighteenth century.
They provided a solution to the problems of overcrowding of urban spaces, since they save
space on the ground. The first skyscraper was built in 1884 in the city of Chicago, Illinois. It was only ten-storeys high. Construction of skyscrapers was aided by the high-speed elevator invented by Otis in 1857. In 1913, the Woolworth Building in New York dared to reach fifty-five storeys, soaring up 241 m. Eighteen years later, the Empire State Building, reached 102 storeys with a height of 381m.
The skyscraper has become the preferred symbol of belonging to the modern, global world. According to the list compiled by the Council on Tall Buildings and Urban Habitat (CTBUH) at Lehigh University, the United States has lost its competitive edge in building tall structures and most of the recent tall structures are in other countries. A distinction has also been made between tall towers (non-habitat structures) and tall buildings. Currently, the tallest tower in the world is the CN Tower in Canada (553m high) and the tallest skyscraper is Taipei 101 in Taiwan (509.2m up to the tip of Antenna/Spire; Roof-449.2m). They are shown in Figure 1 and a comparison of a few completed tall structures is shown in Figure 2.
Both these structures will lose their record this year, due to the opening of Burj Dubai Tower and the construction of the Tokyo Sky Tree. Some details of these structures are presented.
Tokyo Sky TreeThe Japanese are in the process of constructing the world’s new tallest free-standing structure, with a 610m tall Tokyo Sky Tree tower (Figure 3 and 4).
The Tokyo Sky Tree (originally referred to as New Tokyo Tower) is a broadcasting tower currently under construction in Sumida, Tokyo, Japan. If completed as planned, it will be the tallest artificial structure in Japan at 610.58 m tall. The present Tokyo Tower (333 m) is not tall enough for complete digital terrestrial television broadcasting coverage since the construction of many highrise buildings in the central part of the metropolis. The tower will break the record currently held by the CN Tower in Toronto by 57m, and is expected to hold the record for only a few months. Burj Dubai in the United Arab Emirates will in turn shatter the Sumida Tower record when it opens in 2009.
The planning is being led by a group of six terrestrial broadcasters, led by public broadcaster NHK, who plans to complete construction of the tower by December 2011, planned to open to public in spring 2012. The completed structure will be the highlight of a massive commercial development around Oshiage Station.
The tower also has state-of-the-art seismic proofing including a central shaft (made of reinforced concrete) developed from five-tier pagodas that have withstood earthquakes for hundreds of years. Six different names were considered for this tower, viz.,Tokyo Edo Tower, Tokyo Sky Tree, Mirai Tree, Yume Miyagura, Rising East Tower, and Rising Tower. After a nationwide vote, it was officially named as Tokyo Sky Tree on June 10, 2008. Construction of the tower started on 14 July, 2008.
Tallest SkyscrapersSkyscrapers often serve as landmarks and reference points to a city. The tallest building symbolizes national prestige in the form of economic status, growth, technological prosperity and modernity. Hence many countries vie to build super-tall skyscrapers. Table 2 shows some of the tallest skyscrapers of the world. As mentioned earlier, Taipei 101 is holding the current record of tallest skyscraper.
The building resembles the bundled tube form of the Sears Tower, but is not a tube structure. Structural designers purposely selected the shape of Burj Dubai as Y-shaped in plan to reduce the wind forces as well as to keep the structure simple and foster constructability (Figure 6a and 7). The Y-shaped floor plan also maximized the views of the Persian Gulf. Each wing of the Y-shaped tower, with its own high-performance concrete core and perimeter columns, buttresses the other via a six-sided central core, or hexagonal hub (Figure 7). Hence the tower is extremely stiff torsionally. The design team purposely aligned all the common central core and column elements to form a building with no structural transfers. At the top, the central core emerges and is sculpted to form a finishing spire. The spire—itself over 200m tall—will hold communications equipment. Viewed from above or from the base, the form also evokes the onion domes of Islamic architecture.
Each tier of the building steps back in spiral pattern that causes the tower’s width to change at each setback, decreasing the cross section of the tower as it reaches toward the sky. The main advantage of this stepping and shaping is to “scatter the wind”. The wind vortexes never become organized because at each new tier the wind encounters a different building shape that reduces the overall wind load on the structure. The tower, at its tallest point, sways a total of 1.2m.
The exterior cladding of Burj Dubai will consist of 142,000m2of reflective glazing, and aluminium and textured stainless steel spandrel panels with vertical tubular fins. The cladding system is designed to withstand Dubai’s extreme summer temperature. Additionally, at its projected height, the exterior temperature at the top of the building will be noticeably cooler than at its base, by 6°C. Burj Dubai will also feature the world’s fastest elevator, rising and descending at 18m/s. The world’s current fastest elevator (in the Taipei 101) travels at 16.83m/s. A total of 56 elevators will be installed each can carry 42 people at a time.
The tower is being constructed by a South Korean company, Samsung Engineering & Construction which also built the Petronas Twin Towers and the Taipei 101. Samsung Engineering & Construction is building the tower in a joint venture with Besix from Belgium and Arabtec from UAE. Turner is the Project Manager on the main construction contract.
When completed, Burj Dubai’s construction will have used 330,000m3of concrete, 39,000tonnes of steel rebar, and taken 22 million man hours. The foundation of this tower features 192 numbers of 50m long piles. More details about their design and construction may be found from Ref. 2-5.
Under ConstructionThe following super-tall skyscrapers are in various stages of proposal, planning, or construction:
- The Pentominium, under construction in Dubai, is expected to be 618m tall and have 120 floors. Construction began in 2007 and completion is expected by 2011.
- The Russia Tower, under construction in Moscow’s International Business Centre, is expected to be 612.2 m tall and have 118 floors. Construction began in September 2007 and completion is expected by 2012.
- Incheon Tower is a 151-floor, 610m tower in Incheon, South Korea. It is estimated to be completed by 2012.
- The Guangzhou TV & Sightseeing Tower, underconstruction in Guangzhou, China, is expected to be 610.0m tall. Construction began in November 2005 and completion is expected by 2009.
- The Chicago Spire (formerly Fordham Spire), under construction in Chicago, is expected to be 609.6m and have 150 floors. Construction began in June 2007 and completion is expected by early 2012.
- The Jakarta Tower (Menara Jakarta) is currently on-hold in Jakarta, Indonesia. It is expected to be 558m tall up to the antenna, thus may be tallest concrete tower. It is expected to be completed by 2011.
- The Federation Tower East, under construction in Moscow’s International Business Centre, is expected to be 506m tall (to the tip of the spire) and have 93 floors. Construction began in 2003 and completion is expected by 2009.
Proposal for Dubai City Tower
SummaryWhen WTC towers were attacked, doubts were raised regarding the vulnerability of tall buildings to terrorist attack; in spite of these doubts, the world has witnessed the construction of several super-tall buildings in the past. With limited land, skyrocketing land prices and continuous demographic explosion in big cities worldwide, there is no other possibility than to build high-rise structures.
The current record holders of tall structures may loose their title when new buildings are completed (which are happening are regular intervals). When completed, the Burj Dubai Tower will be the world’s tallest structure. It represents a significant achievement in terms of utilizing the latest design, materials, and construction technology and methods, in order to provide an efficient, rational structure to rise to heights never before seen. We may expect to see more and more steel, concrete and composite high-rise structures shaping the skylines of major cities of the world in the forthcoming years.
- Subramanian, N, Collapse of WTC-Its inpact on skyscraper construction, Indian Concrete Journal, V. N.3, Mar. 2002, pp.165-169.
- Baker,W. F., The World’s tallest building, Burj Dubai, U.A.E., CTBUH conference, Seoul, Oct 10-13, 2004, pp.1168-1169
- Baker, W. F. , Korista, D. S., and Novak, L. C., Burj Dubai: Engineering the World’s Tallest Building, CTBUH / Wiley Tal Journal, 2007, pp. 361–375
- Lee, H.J., Kuchma, D.A., Baker, W., and Novak, L.C., Design and analysis of heavily loaded reinforced concrete link beams for Burj Dubai, ACI Structural Journal, V. 105, No., 4, July-Aug.2008, pp.451-459
- Irwin, P.A., and Baker, W.F., The Burj Dubai Tower- Wind engineering, The Structure Magazine, SEI/ASCE, June 2006, pp.28-31