|Dr. N. Subramanian
Joined: 21 Feb 2008
Location: Gaithersburg, MD, U.S.A.
|Posted: Thu Sep 29, 2011 3:54 am Post subject: Kingdom Tower-Tallest building in the World
|Kingdom Tower,Jeddah, Saudi Arabia
Kingdom Tower, previously known as Mile-High Tower is a supertall skyscraper approved for construction in Jeddah, Saudi Arabia at a preliminary cost of US$1.23 billion. It will be the centerpiece and first phase of a US$20 billion proposed development known as Kingdom City that will be located along the Red Sea on the north side of Jeddah.
If completed as planned, the tower will reach unprecedented heights, becoming the tallest building in the world, as well as the first structure to reach the one-kilometer mark. The tower was initially planned to be 1.6-kilometre (1 mile) high; however, the geography of the area proved unsuitable for a tower of that height. The design, created by architect Adrian Smith, incorporates many unique structural and aesthetic features. The creator and leader of the project is Saudi Arabian Prince Al-Waleed bin Talal, the wealthiest Arab in the Middle East, and nephew of King Abdullah. Talal is the chairman of Kingdom Holding Company (KHC), the largest company in Saudi Arabia, which owns the project, and a partner in Jeddah Economic Company (JEC), which was formed in 2009 for the development of Kingdom Tower and City. Reception of the proposal has been highly polarized, receiving high praise from some as a culturally significant icon that will symbolize the nation's wealth and power, while others question its socioeconomic motives, and forecast that it will actually have negative financial consequences.
The tower is being designed primarily by Chicago-based architect Adrian Smith of Adrian Smith + Gordon Gill Architecture (AS + GG),the same architect who designed the Burj Khalifa while he was working for Skidmore, Owings & Merill (SOM), for which he worked almost 40 years. AS + GG was formed in 2006 by Adrian Smith, Gordon Gill, and Robert Forest. The development of the tower is being managed by Emaar Properties PJSC. Thornton Tomasetti has been selected as the structural engineering firm, and Environmental Systems Design, Inc. (ESD) is a part of the AS + GG design team that serves as the building services engineering consultants.
The triangular footprint and sloped exterior of Kingdom Tower is designed to reduce wind loads; its high surface area also makes it ideal for residential units. The overall design of the tower, which will be located near both the Red Sea and the mouth of the Obhur Creek (Sharm Ob'hur) where it widens as it meets the Red Sea, as well as having frontage on a man-made waterway and harbor that will be built around it,is intended to look like a desert plant shooting upwards as a symbol of Saudi Arabia's growth and future, as well as to add prominence to Jeddah's status as the gateway into the holy city of Makkah (Mecca).The designer's vision was “one that represents the new spirit in Saudi Arabia" (Smith). The 23 hectare area around Kingdom Tower will contain public space and a shopping mall, as well as other residential and commercial developments, and be known as the Kingdom Tower Water Front District, of which, the tower's site alone will take up 500,000 m2. As with many other very tall skyscrapers, including the Kingdom Centre in nearby Riyadh, which is generally considered to have sparked the recent significant commercial developments around it in the district of Olaya, much of the intention of Kingdom Tower is to be symbolic as well as to raise the surrounding land value rather than its own profitability. To that effect, the tower's architect, Adrian Smith, said that the tower "evokes a bundle of leaves shooting up from the ground–a burst of new life that heralds more growth all around it". Smith states that the tower will create a landmark in which it and the surrounding Kingdom City are interdependent. Talal Al Maiman, a board member of Jeddah Economic Company, said, “Kingdom Tower will be a landmark structure that will greatly increase the value of the hundreds of other properties around it in Kingdom City and indeed throughout North Jeddah.” The concept of profitability derived from building high density developments and malls around such a landmark was taken from the Burj Khalifa, where it has proven successful, as its surrounding malls, hotels and condominiums in the area known as Downtown Dubai have generated the most considerable revenue out of that project as a whole, while the Burj Khalifa itself made little or no profit.
The large, outdoor sky terrace will overlook the Red Sea and have an area of over 697 square metres
A rendering showing the bottom of the unique, glass-floored, circular sky terrace that will overlook the Red Sea from over 610 metres
The building will have a total of 59 elevators, five of which will be double-deck elevators, as well as 12 escalators. It will also have the highest observation deck in the world, to which high speed elevators will travel at up to 10 meters per second (slightly over 35 km/h) in both directions. The elevators cannot go faster because the rapid change in air pressure over that much distance would be nauseating; at 914 m , the air pressure is over 10 kPa lower than at ground level (about 10% less air pressure). They must also be efficient so the cables are not unbearably heavy.Even as such, the elevator distance limit is about 570 metres before the cables become inevitably too heavy and the motor size impractical; Kingdom Tower will have three sky lobbies where elevator transfers can be made, no elevator will go from the bottom to the highest occupied floor.No official floor count has been given, however Smith stated in a television interview that it will be about 50 floors over the Burj Khalifa, which has 163 occupied floors, leading to the inference that Kingdom Tower will have well over 200 floors. The tower will also feature a large, roughly 30 m diameter outdoor balcony, known as the sky terrace, on one side of the building for private use by the penthouse floor at level 157; it is not the observation deck. It was originally intended to be a helipad, but it was revealed to be an unsuitable landing environment by helicopter pilots.
The building's large notches will also serve as shaded terraces for other areas of the tower and the exterior of the building will use low-condusive glass to save on cooling costs by reducing thermal loads. In addition, the lower air density, exacerbated by the thin desert atmosphere, will cause the outdoor air temperature towards the top of the tower to be lower than the ground level air, which will provide natural cooling. There is also significantly more air flow (wind) at heights, which is very strong at one kilometer and had a large impact on the structural design of the tower. The Burj Khalifa actually takes in the cooler, cleaner air from the top floors and uses it to air condition the building. Kingdom Tower will be oriented such that no façade directly faces the sun; it will also use the condensate water from the air conditioning system for irrigation and other purposes throughout the building.
Chicago based Environmental Systems Design will provide mechanical, plumbing, electrical and fire protection engineering, as well as teledata, audio/visual, security systems and acoustics. Langan International, together with structural engineer Thornton Tomasetti, will be responsible for geotechnical engineering as well as some ground level site work such as transportation engineering and parking, including the design of the proposed 3,000–4,700 car underground parking garage that will be located near, but not under the tower for terrorism reasons. Langan also designed the tower's foundation, which has to be able to support the tower despite the less than optimal subsurface conditions, such as soft rock and permeable coral, which could cause the piles to settle.
Thornton Tomasetti has provided the structural engineering for two of the previous world's tallest building title holders, the Petronas Towers in Kuala Lumpur, and the Taipei 101 in Taiwan, as well as the under construction Pingan International Finance Center in Shenzhen, which will be the tallest building in China after completion. Saudi Binladin Group is the largest construction firm in the Middle East, with over 35,000 workers and hundreds of projects. They recently constructed the topped-out 601 m Abraj Al-Bait Clock Tower in Mecca, which is the tallest building in Saudi Arabia and second tallest in the world, as well as the largest skyscraper in the world by floor area and volume. Aside from buildings, the firm has also constructed many major infrastructure projects, such as the King Abdulaziz (Jeddah) International Airport expansion and the 775 km six lane Al Qassim Expressway through Saudi Arabia. Saudi Binladin Group is owned by the family of the late al-Qaeda leader Osama bin Ladin whom the family disavowed long before his death. Nonetheless, it has sparked some minor media buzz. When asked his thoughts about this in an interview, Adrian Smith simply stated that they are the largest construction firm in the Middle East, most significant work in Saudi Arabia was done by them, and that it is a very large family that shouldn't be stereotyped by one of its members.
“An elegant, cost-efficient and highly constructible design.”
— Adrian Smith, architect of Kingdom Tower
In addition to its primary functions, the building is slated to include a significant amount of retail as well as a wide variety of other unique ammentities with the intention that it functions as a nearly self-sustaining entity, approaching the concept of a "vertical city".The building's design has been applauded as simplistic and buildable, yet bold, brilliantly sculpted, and high-tech, with AS + GG describing it as "an elegant, cost-efficient and highly constructible design." The estimated construction cost of US$1.23 billion, which is less than that of the Burj Khalifa (US$1.5 billion), can be attributed to cheap labor in the Middle East, particularly Saudi Arabia, and that three shifts will work around the clock to expedite the process. Construction costs have also declined since the global financial crisis.
“At extreme heights, the main challenges are along practical and architectural lines, not material or structural.”
— Bob Sinn, principal of Kingdom Tower engineering firm Thornton Tomasetti
In July, 2011, a report by consultancy EC Harris found that Saudi Arabia is the cheapest country in the Middle East to build in, half as expensive as Bahrain, and 34% cheaper than the United Arab Emirates, where Burj Khalifa is located. The future towers' site is located in very close proximity to King Abdulaziz (Jeddah) International Airport, whose runways nearly align with the towers' site, which will have an effect on the airspace. While skyscraper experts have stated that towers well over one kilometer, even two kilometers high, are technically buildable, physical sustainability and practicality issues come into play in towers of this height. From a real estate perspective, it is considered virtually impossible to create enough demand to justify such a tower, but that at some point someone with a great excess of money will likely do it anyway. As for physical restraints, Bart Leclercq, head of structures for WSP Middle East recently said, “I truly believe that 1 mile—1.6 kilometres—is within range. Over that, it may be possible if there are improvements in concrete quality. But 2km is too big a figure –it’s just a step too far at the moment.”
“Kingdom Tower’s height is remarkable, obviously, but the building’s iconic status will not depend solely on that aspect. Its form is brilliantly sculpted, making it quite simply the most beautiful building in the world of any height.”
— Talal Al Maiman, board member of Jeddah Economic Company
Sustainability of such a tall building would include issues such as vertical transportation limitations, with elevators only being able to go so far, building sway, caused by wind, and supercolumn settling, which is where the steel columns settle more than the concrete core and cause the floors to be unlevel. Additionally, a very large core size is required in very tall buildings to support the structure as well as to house the large number of elevators needed. The core size consumes a significant amount of the space on the lower and middle floors.One of the ways Kingdom Tower attempts to overcome these issues is with its smooth, sloped-exterior design, which, although more expensive to build, offers superior aerodynamic performance over "stepped" designs such as the Burj Khalifa, allowing it to have a more conservative core overall. This was determined by wind tunnel tests performed at Burj Khalifa. Kingdom Tower will also utilize copious stiffening materials to prevent the excessive sway that would otherwise make the occupants of upper floors nauseous on windy days, including very high strength concrete that will be up to several feet thick in certain parts of the core. This, along with the highly integrated steel frame and shear walls, is also intended to prevent catastrophic failure of the structure in the event of a terrorist attack. Traditionally, these physical constraints, namely the space consumed by elevators, were considered to make a building become increasingly less profitable past 80 floors or so. More recently, it has been the advent of truly mixed-use design such as Shanghai Tower and Burj Khalifa, as well as improved building technology, that have outdated this rule of thumb, which generally applied to single use buildings.
“Is there such as thing as too high? I think mankind is always going to be challenged by finding the next frontier. I think there’s also a market -people will always want to be in the world’s tallest tower.”
— Bart Leclercq, head of structures for WSP Middle East
Both towers share a similar three-petal triangular footprint for stability and a tapering form, with sheer height and wind being the biggest structural design challenge. The smooth, sloped façade of Kingdom Tower particularly induces a beneficial phenomenon known as "wind vortex shedding," whereas normally when wind swirls around the leeward side of a building, rushing in from both sides to fill the low pressure zone, it would create tornado-like vorticies, which would rock the building from side to side due to the variances in pressure, direction, and velocity, the dynamic façade of Kingdom Tower creates an infinite timing differential (wheras Burj Khalifa is limited by the number of steps) in air pressure exertion in any one particular direction, thus creating a more stable structure, as there is no broad area of outstanding pressure or depression at any given time. Put simply, a smooth taper is more aerodynamic than an irregular or jagged taper, while both are advantageous over rectangular geometries. At Kingdom Tower's height, it is considered essentially unfeasible to use a traditional square design.
To overcome elevator issues, the tower will use its large number of efficient elevators as well as its three sky lobbies, which allows transfers to be made between elevators serving a specific area with no elevator being overburdened. Much was learned from Burj Khalifa that helped with the design of Kingdom Tower not only structurally, but in methods for designing practical mechanical, electrical, and plumbing (MEP) systems, as well as adhering to local regulations and international building codes. Despite all the physical challenges, Adrian Smith states that practicality is still the greater challenge over structural durability, even in such super tall designs, and that as with all buildings, Kingdom Tower's form and was primarily derived respective of what the building's uses would be, then in accordance with the structural factors that would have to be considered to deliver it.
Aside from the geotechnical investigation (soil testing) that took place in 2008, and minor site preparation evidenced by pictures of the site, work on the foundation has not yet begun. While the official construction estimate is five years and three months , others calculate that it will take significantly longer, over seven years, based on the duration of Burj Khalifa's construction, which was over six years. Statements that construction will begin soon have been made since 2008, but have been postponed each time. As of August 2011, the construction schedule has been slated as "no later than December," with some saying "immediately," and that construction is imminent. This means the tower is expected to be completed during the year 2017, though it is possible that it could be completed by the date the media continues to publish, which is the prior estimate of late 2016. Only if construction does begin promptly and go smoothly can a late 2016 completion be expected. Designs for the foundation were in place by early August and the contract for the piling with Langan International was being tendered.
On 16 August 2011, Langan officially announced their involvement and that the foundation and piling had to be uniquely designed to overcome subsurface issues such as soft bedrock and porous coral rock, which normally could not support a skyscraper without settling. The foundation will be similar to that of the Burj Khalifa, but larger. It is expected to be around 60 m deep with a concrete pad of around 7,500 m2 . The concrete will have to have low permeability to keep out corrosive salt water from the Red Sea, its depth and size is also considered to be an indicator of what the tower's final height will be. The piles will be up to 200 m deep and the pad over 91m across, yet even still the building, which will weigh over 900,000 tons, is expected to settle. The idea is that it settles evenly enough so that the building doesn't tip or put undue stress on the superstructure. Computer modeling programs performed tests at the site to confirm that the foundation design would work.
Construction of the building will rely on cutting edge technology, including the high-strength reinforced concrete and the pumps used to elevate it to record heights, similar to what was used during Burj Khalifa's construction. Bob Sinn, principal of Thornton Tomasetti states, “Concrete quality is getting better and better, as is pumping technology. There have been very strong advances in reinforced concrete over the last 20 years." He continued, “Kingdom Tower is certainly feasible. It’s not a structural challenge. Technically
I think a 2 km -tall tower could be done, but I don’t think it will be done anytime soon.” Kingdom Tower is not only the only approved structure over 1,000 m, it is also the only proposal higher than the 828 m Burj Khalifa to be given the green light for construction.
For more info:
3. Jenny, J., World's Tallest Building must be More than tall, Civil Engineering, ASCE, Sept 2011, pp.16-17