The focus of a building is primarily for shelter, protection and a way to acclimatize comfortably from the outside world. As time has progressed, new ways of providing shelter have been developed, and in many cities, skyscrapers have become a home to many. These taller buildings have allowed cities to become more compact, allowing more people within a closer distance. Modern skyscrapers include much more than just offices and apartments, some provide entertainment, leisure facilities and food outlets meaning occupants never need to leave the building. Currently, there are over 110 buildings over 300 metres high worldwide, and this number is growing yearly (CTBUH, 2016). In this report, I will explore the features of today’s skyscrapers and how we have designed them intelligently to be environmentally conscious. I will also consider future designs and explore whether they are reasonable.
History behind skyscrapers
The skyscraper that people recognize as the first, is the Home Insurance Building in Chicago, USA (History.com, 2010) – see figure 1. Construction started in 1884, and the building opened in 1885, towering over most buildings at only ten stories high. Many consider this as the first skyscraper due to it having a steel load bearing frame embedded in the masonry. (Guinness World Records, 2016b). The idea of using steel framework has proved reliable as it is what many high-rise buildings use these days, due to it being safer and easier to shape for more interesting designs.
Why do we build skyscrapers?
Other than the useful practical properties of skyscrapers, such as to house many commercial offices within a small area of land, there are other reasons people build them (Why Do, 2013). As humans, we always challenge ourselves and aim for better, and building as high as possible has always been an endless goal. Ultimately skyscrapers are a symbol of wealth and success. Towering over everyone and everything can give people a sense of power and importance. Skyscrapers may be looked upon as status symbol, this is due to many skyscrapers only being available to the rich and elite.
How are they supported?
Although Skyscrapers supply us with many useful properties, they are complex and seen as a challenge to many engineers. They require strong, stiff materials to be able to withstand the forces from its own weight as well as the forces of nature such as earthquakes and wind. Concrete is used mainly for the supporting columns and floors as it is good at withstanding the compressive forces of the building. Steel is used as a frame because it can be used in compression and tension, which is good for a skyscraper as it sways and moves more than a lower-rise building. The higher the building is, the more force being directed down into the ground and onto the columns at the bottom. The columns at the top are only designed to take the necessary force of the roof and its own floor, so the lower the position of the column, the more force it will support. This is also why cladding, such as glass or aluminium is used, as concrete or masonry would add too much unnecessary weight onto these supports (Economist T, 2006).
Problems associated with skyscrapers
One problem of a skyscraper is moving services to the top of the tower, such as water, lifts, and emergency services (Economist T, 2006). As the tower height increases, the population of people and demand for services will increase, putting strain on systems within the tower. In a video interview, professionals were asked the question ‘What do you think is the single biggest limiting factor that would prevent humanity creating a mile-high tower or higher?’ (Limiting factors of mile-high towers?, 2011). Architects Adrian Smith and Chris Wilkinson stated in an interview that lift strategy would be the limiting factor and finding a way to create a lift system that can service the whole tower and large population of people would be the most difficult task. Another engineer, Werner Soberk, thought building a mile-high tower is possible, but allowing it to integrate into the surrounding city and promoting social cohesion would be challenging. He said through environmentally friendly transportation between buildings of this type, the idea could work and prove to be useful in creating a smart city (Limiting factors of mile-high towers?, 2011).
Natural ventilation within skyscrapers is difficult as it’s too windy and unsafe to open any windows at a high height. As a skyscrapers’ height increases, the energy increase is imagined to be quite large compared with many low-rise buildings. A study of 20 Hong Kong high-rise buildings in 2003 found that as the height increased of high-rise buildings, there was a steady increase in energy consumed by the tower. The study showed it increased approximately by 3kWh per metre squared per floor (How green is your skyscraper?, 2016). There are ways we can work around this by designing the building specifically around its natural environment. For example, using the direction of the prevailing wind and using vents on the wall of the tower to supply natural ventilation inside, as this will reduce the energy needed for air conditioning, which can take up to 25% of the energy used (Conca J, 2016). One other method could be to use solar panels on the sides of the buildings. Stauffer (2013) has shown through research at MIT that transparent solar cells can be created so that they can be used as windows or other surfaces whilst still absorbing infrared and ultraviolet light (Stauffer N, 2013). The only downside is that they are expensive and using wind turbines may be more cost efficient for the energy provided per turbine on a large enough scale (Boxwell M, no date).
Case Study – Burj Khalifa
The Burj Khalifa is known around the world as the tallest skyscraper in the world at 828m and over 160 stories (PJSC E, 2016b). It holds many world records such as highest observation deck and the elevator with the longest traveling distance and highest speed of 10m/s (Dombrowski J, 2012). The construction work on the tower began in January 2004 and took six years (PJSC E, 2016a), and $1.5 billion until the skyscraper opened in 2010 (Thomas D, 2012). Engineers had many struggles with design and construction. Wind was one of the main factors that had to be considered during the design. Wind speeds in the dessert can range from 12km/h to 80km/h so the building had to be able to withstand high lateral forces. The engineers produced a design that allowed the wind to flow around the building. The ‘Y’ shape of the building allowed the opposite wing of the building to act as a buttress (buttressed core as seen in figure 6), pushing back against the force of the wind on the other sides (as seen in figure 7) (Berg N, 2012).
Providing water 160 stories high had never been done before. Engineers used a very powerful motor which produced a pressure of over 80MPa to pump the water over 100 floors (Challenges & Innovations, no date). It uses a lot of energy, but with the skyscraper being in the middle of a dessert it is difficult to collect water through methods such as rainfall collectors.
Architects have already designed mile high tower concepts such as one in Tokyo predicted to be constructed by 2045 (Chung S, 2016). Currently, a 1km tall building in Jeddah, Saudi Arabia is being constructed and is to be completed by 2020 (Jeddah Tower, no date). It will have approximately 65 elevators and an observatory at 637.5m high. (Wright H, 2015).
Using skyscrapers within cities
Although people may think building higher allows a denser city to grow, in Manhattan, NY, the average density of people is 27,000 people per Km2, cities such as Paris and Barcelona have managed to achieve this density by building midrise apartment blocks close together (Ijeh, I, 2015). This is a questionable figure to whether population density is a good argument for building high, as there may be more efficient ways to do so. There are issues with building close in cities, such as the urban heat island effect which is predicted to worsen with global warming; cities will become uncomfortably hot (Musco F, 2016). An example of a cleverly designed city is a project called Heart of Doha as seen in Figure 5. Here they’ve angled buildings to maximise wind flow and natural ventilation (Heart of Doha, 2011). In my opinion, for skyscrapers work well for cities they must be close together and be appealing to people, whilst affordable. They need to encourage social cohesion and promote the reduction of people needing to travel far. If people live closer to everything they need, it is easy for them to walk, therefore reducing the level of CO2 released by the transport systems and cars. Creating the ultimate smart city should be our aim.
Conclusion
This report has shown that the popularity of skyscrapers has increased, with over 3726 worldwide (CTBUH, 2016). It has also indicated that there are problems with building very high. Mile high towers are possible whilst challenging, but they are not the best use of money or materials. It may be more cost effective and practical to build smaller skyscrapers due to the safety risks involved and difficulties in ascending the tower quickly and easily. Skyscrapers have evolved to become taller, safer and stronger. Although this will continue to happen, further development in transportation methods within skyscrapers is needed before it’s realistic to live and work that high.