Jeddah, Saudi Arabia, has long served as a port for Muslims arriving by sea for the Hajj, the annual Islamic pilgrimage to Mecca. With a population of 5.1 million, Jeddah is the second largest city in Saudi Arabia and ranks as the largest city on the Red Sea. If all goes as planned, by 2020 pilgrims flooding the city will be treated to a modern marvel, a skyscraper more than 1 km in height called the Kingdom Tower.

Prince Al-Waleed bin Talal bin Abdulaziz al Saud, chairman and CEO of the Kingdom Holding Co., which is building the Kingdom Tower, has a vision for Jeddah. On a 5.2 km² plot, 20 km north of Jeddah, he plans to build Kingdom City, an ultra-modern district. At a cost estimated at $20 billion, it will take 10 years to construct with the Kingdom Tower built in the center. At 1 km in height, the Kingdom Tower will soar over Kingdom City and Jeddah. Preliminary estimation places the cost at $1.23 billion for the tower alone, a price that is most likely to go up if the $1.5 billion price tag of the current tallest building in the world (at 830 meters), the Burj Kalifa in Dubai, UAE, is any indication.

Kingdom Tower is under construction and is slated to be the first building to exceed 1 km in height. Image source: Wikipedia

The tower, already under construction, is slated to be finished by 2020. It will be the first building to exceed 1 km in height with 167 floors and a floor area of 319,000 m². It will contain 59 elevators, 54 single and 5 double-deck elevators. The building will have the highest observation deck in the world at 500 meters. The architect is the American Andrain Smith, designer of the Burj Kalifa.

Onwards and Upwards

The world is in the midst of a skyscraper boom with 19 of the 20 tallest skyscrapers having been built in the past 20 years. Even the 442 meter Willis Tower (formerly known as the Sears Tower), which stood in Chicago, Ill., as the tallest building in the world as recently as 1998 is now the 12th tallest in the world. (For more on these tall buildings, see our infographic.)

The 601 meter Mecca Royal Hotel Clock Tower in Mecca, Saudi Arabia is among the five tallest buildings in the world. Image source: Wikipedia

The top five tallest buildings (completed) in the world are the Burj Khalifa; the 601-meter Mecca Royal Hotel Clock Tower in Mecca, Saudi Arabia; the 541.3-meter One World Trade Center in New York City; the 509-meter Taipei 101 in Taipei, Taiwan; and the 492-meter Shanghai World Financial Center in Shanghai, China. In the next two years, two buildings in China are expected to crack the top five: the 530-meter CTF Finance Centre in Guangzhou and the 632-meter Shanghai Tower.

Much of the recent boom in skyscraper construction can be attributed to economics. Oil-wealthy nations and the rapidly growing nations of Asia account for nine of the top 10 tallest skyscrapers. However, technological breakthroughs over the past half century have also made mega-skyscrapers possible.

Managing Loads

When building a skyscraper, among the most important structural factors are the vertical dead load (the weight of the building upon itself) and wind loading, the result of increasing wind pressure with increased height. The goal in constructing skyscrapers becomes a game of resisting the increasing lateral loads (caused either by strong winds or earthquakes), while managing vertical loads by reducing the weight of construction materials.

In the first half of the 20th century, skyscrapers were constructed using rigid steel frames. These frames consisted of vertical steel columns and horizontal T-beams constructed in a rectangular grid to support the building's floors, roof and walls.

Tubular Breakthrough

In the 1960s, Fazlur Rahman Khan, designer of the Willis Tower, introduced tubular structural systems. These structures are stiff and have significant advantages over traditional steel frames. Because they are stiffer, they are better at resisting lateral loading and, thus, less material is needed during construction. This lowers both material costs and vertical loads.

The style was improved later with innovations such as the tube-in-tube and bundled tube approaches, the latter used in constructing the Willis Tower. Not only did this innovation greatly reduce vertical loads and material costs, it also increased the availability of floor space and opened the possibility of multiple skyscraper shapes beyond the box shapes demanded by steel frames.

Elevator Innovation

Skyscrapers would be impractical if not for elevators. Elevators evolved from novelties to the workhorses of tall buildings during the 19th century and early 20th centuries. As buildings grew taller, more elevators were needed to service the buildings.

Elevators are usually centrally located in a skyscraper and take up valuable floor space. To compensate for this, in the later 20th century, the idea of sky lobbies was introduced. In this concept, a set of elevators services a tower's lower floors and another set of elevators services the higher floors. One floor about halfway up the skyscraper acts as something like the ground floor for that second set of elevators, and is sometimes called a "sky lobby." A few express elevators go directly to the sky lobby. This seemingly small innovation has saved considerable floor space and improved the economics of skyscrapers.

Scraping the Sky

Originally, the Kingdom Tower was designed to be one mile high, or 1.6 kilometer. Later analysis of the surrounding soil determined that the building might not be stable at that height. Soil conditions aside, current construction methods suggest that there is no reason why a mile-high skyscraper could not be built. In fact, several skyscrapers which are currently under construction are designed to exceed 600 meters.

These include the 729-meter Suzhou Zhongnan Center in Suzhou, China; the 660-meter Ping An Finance Center in Shenzhen China; the 626-meter Wuhan Greenland Center in Wuhan, China; and the 610-meter KL118 Tower in Kuala Lumpur, Malaysia. No skyscrapers are currently being constructed, however, that will approach the Kingdom Tower’s height.

Question or comment about this article? Contact the editor: engineering360editors@ihs.com