Monday, May 9, 2016

Is there a limit to how high we can build?



On May 6th 1954 when Roger Bannister broke the four minute mile, there were many who thought that this would never be beaten.  The record has been broken a further eighteen times since then..... This also seems to be the case with high rise buildings, motivated by our human desire ‘to go one better’ than the previous best.

Burj Khalifa Tower - Source: www.youtube.com
Sometimes we have to stand in awe at the creativity and innovativity of the human race, where we are constantly stretching the boundaries of possibility. This is well demonstrated around the globe with the large amount of high rise buildings that are either in the process of being constructed, or have actually been completed. Demand for high rise buildings is on the increase, which is demonstrated by the Council on Tall Buildings and Urban Habitat (CTBUH), who have formulated a list from their database which shows completed, under construction and planned ‘skyscrapers’ over the coming years.  Click on this (link) to take a look at this list where you will notice that if all of the proposed and under construction buildings are completed, then by 2021, only three of the current top 10 buildings (Burj Kalifa, Shanghai Tower and Makkah Royal Clock Tower), will remain in the top 10 buildings, and in fact only five of the current top 20 buildings, will still appear in the top 20 by 2022.  These statistics are staggering, however they demonstrate our inate desire to build big.  At the top of the list of proposed tall buildings is the Kingdom Tower in Jeddah, Saudi Arabia. This is now under construciton and projected for completion in 2018. It is expected to cost in excess of $1.2bn, and form the first phase of a wider Kingdom City scheme that is estimated in the region of $2bn.  Kingdom Tower will rise to 1000 metres, which will exceed the current completed tallest building (Burj Kalifa – Dubai), by a further 172 metres.

The tallest building in the European Union is currently The Shard’ in London. Completed in 2012. The building stands at what now seems to be a modest 309.6 metres, when you take into consideration the buildings on the CTBUH list.  In fact if all of the under construction and planned buildings on the list are completed, The Shard will not even appear in the top hundred and fifty buildings in the World by 2021, even though it currently sits as the 80th highest completed building in the World.

Kingdom Tower, Jeddah - Under Construction - Source: www.youtube.com
There are a number of reason that may motivate investment in a high rise building, including, scarcity of land in large cities (often their central business districts), increasing demand for business and residential space, economic growth, human aspiration to build higher, innovations  in structural systems and products and ultimately prestige. However, planning and constructing a large building comes with many challenges that are less of an issue for smaller buildings.  This includes things such as finance, planning restrictions, energy use (although many new buildings are adopting renewable and other technologies), structural considerations, circulation in what effectively becomes a vertical street, external fa├žade (fixing, maintenance and cleaning), internal environment to achieve human comfort, and so on.  The more high rise buildings that are built, then the more these issues are better understood, however as we stretch the boundaries and construct even higher, then we are likely to encounter further obstacles that we may not have previously contemplated.

As an example let us consider one of the fundamental needs, water supply, in a very high building.  If we consider the provision of a water supply pipe from the bottom of the building to the top, it is easy to imagine why this could prove to be problematic.  As previously stated the current highest building in the World is 828 metres high.  Therefore trying to ensure that the water supply travels such a long distance in a vertical direction and can be used at the right pressure when needed is never going to be straightforward:

‘Plumbing is one of the more challenging problems to solve due to the loss in pressure as water travels up a vertical pipe. Plumbing engineers found out that as you lift water above a datum, you lose 1 pound per square inch for every 2.3 feet of elevation. This small but incremental loss makes achieving high water pressure at the top of a water column very difficult. Most water fixtures require at least 25 psi to operate or flush properly, so measures to ensure consistent water pressure throughout the building must be implemented. As the building get taller, another problem arises as the water pressure at the bottom of a vertical pipe becomes too great for safe operation and building codes’
                       
‘The early solution to this problem was a water tank mounted on the top of a building with fill pumps at the bottom of the building.  Water is supplied to occupants through a simple gravity down feed system.  Today, a system of pressure-reducing valves and sub-risers are used to manage the inconsistent water pressure throughout a skyscraper. Pressure-reducing valves reduce the pressure at the bottom of the building, while sub-risers increase the pressure for the skyscrapers upper floors. Today’s systems lack a main tank, but rather integrate the whole system within a buildings walls and basement’ (Source: http://www.allaboutskyscrapers.com/)

The above discusses a single issue to demonstrate the complexity of design issues in respect of building higher. Other issues such as sewage, lifts, emergency escape, fire fighting provision, earthquakes (and many others ) etc. could equally have been selected, as they pose significant design challenges for very high buildings.  Despite this it appears from buildings on the CTBUH list, that these issues are not standing in the way of buildings becoming evermore higher. This then poses a question. ‘Is there a limit to how high we can build?’ Well, at present it appears not, but surely there has to be a limit?  On May 6th 1954 when Roger Bannister broke the four minute mile, there were many who thought that this would never be beaten.  The record has since been broken a further eighteen times since then, with the current record being held by Moroccan, Hicham El Guerrouj achieving a time of 3.43.13 in Rome in 1999.  This also seems to be the case with high rise buildings, motivated by our human desire ‘to go one better’ than the previous best.

Who knows what human ingenuity will produce in the future? The possibilities seem endless. In fact take a look at the list of ‘all’ tall buildings on the CTBUH database and you will see that there is a ‘vision’ to build at a height of 4000 metres in Tokyo, Japan. This is four times higher than the Jeddah Tower which will become the new highest building in the World when completed in a few years time. This vision appears hard to believe however I am sure many thought the same about a human being running a mile in less than four minutes prior to 1953, so you never know……..

Try to take the time to look at this fascinating documentary which shows how the current highest building in the World was constructed.


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