Green giants

Modern high rise buildings are often viewed as iconic statements of a city's wealth and status. The rivalry between nations to have the tallest building is ongoing but a new trend is emerging – the challenge to build the greenest skyscraper. Claire Symes reports.

Construction work on the 800 m plus Burj Dubai development means that Dubai will soon claim the world's tallest building title from Taiwan's 509 m tall Taipei 101 tower. But Dubai's claim may be short lived if Kuwait gives the final go ahead to the 1001 m tall 250-storey Mubarak Tower, which will include a school, medical centre and a mosque.

Kuwait is a low energy city and, according to the project's structural engineer Atkins, the final design of the Mubarak Tower will have to take this into account. But the Mubarak Tower is not the only high rise project that is looking at lowering its environmental impact. In fact, the challenge to build the greenest skyscraper is shaping up to rival the race for the skies.

“High rise developments are already environmentally friendly solutions for urban areas because they take up a lot less room than the equivalent floor space spread over low rise developments,” said WSP Cantor Seinuk director Ron Slade. “Skyscrapers are also robust structures with a long service life, which can be 'recycled' through refurbishment. The Rotunda in Birmingham, UK, for example, is in the final stages of reconstruction after being stripped back to its frame to convert it from office space to a luxury residential development.”

Nonetheless, many high rise developers are including new green technologies into the structure of their buildings to further reduce their environmental impact.

“Clients and architects want to differentiate their high rise development from other designs. This used to be done by achieving new heights but attention is now turning towards reaching new environmental standards,” said Mr Slade. “The move to reduce the environmental impact is also being driven by corporate social responsibility of companies developing buildings for their own use. Investment bank Swiss Re's St Mary Axe tower in London, UK, for example, is naturally ventilated because the company wanted to reduce reliance on air conditioning systems.”

Another high rise that is being driven by the developer's corporate social responsibility is the US$ 1 billion Bank of America Tower in New York, US. When complete in 2008 the 54-storey glass clad project's developers – a joint venture of the Bank of America and the Durst Organisation – expect it to be one of the most environmentally friendly high-rise structures in the world. The design aims to reduce energy and water consumption by up to -50% and features grey water recycling, use of recycled and recyclable materials and a 4.6 MW cogeneration plant.

Tax benefits exist in some countries for developing more environmentally friendly buildings, which makes such developments more attractive to prospective tenants. Another building – The Helena – funded by the Durst Organisation is currently being built in Manhattan, New York in the US, using a 45% slag cement concrete for the structure's concrete frame.

The 40-storey residential Helena tower is the first time such a high percentage of slag cement has been used in a high rise development in New York. Its use will qualify the building for the New York State Green Building Tax Credit. But for the team working on site, the slag cement has had some additional benefits in achieving very high early strength, which has allowed for faster construction cycles.

“The trend towards greener buildings started in Western Europe and North America but is now beginning to spread to China and the Middle East,” said Mr Slade.

Construction of the Bahrain World Trade Centre is due to be completed later this year and the project's engineer Atkins claims it is the world's first large scale integration of wind turbines into a building. The two 50-storey sail shaped towers will support three 29 m diameter wind turbines that are expected to provide up to 15% of the building's annual energy needs.

Atkins engineering head of technology Richard Smith said, “Our client wanted to use this building to demonstrate Bahrain's commitment to reducing demands on fossil fuel energy reserves. Integrating large-scale wind turbines into a building has been a complex task but the knowledge and experience gained on this project will be shared around the world.”

In fact, the knowledge gained from the Bahrain project is also being fed into Atkins' other high rise developments. The company recently announced that its sustainable design had helped it to win a competition to build the Teda Towers, a complex of three skyscrapers in Tianjin, China.

The tallest of the three towers will reach 356 m – the others will be 198 m and 136 m tall – and, when completed in 2009, the structures will resemble blocks rotating around a central core. Similar to the Bahrain World Trade Centre, the Teda Towers will feature vertical wind power electricity generators on top of each tower to provide supplementary energy. The towers will also use ground water for heating and cooling.

Design influence

But the move towards green technologies is more fundamental and is actually beginning to affect the aesthetics of high rise developments.

The fully glazed 310 m tall Ocean Heights One tower at Dubai Marina, which was designed by Hong Kong-based architect Aedas, twists as it rises. According to Aedas, the shifting profile allows every apartment to have a sea view but the design also minimises heat gain and provides shading to balconies during the middle of the day.

“Translucent buildings are very fashionable at the moment and give designers the opportunity to use natural lighting, but this needs to be balanced with solar (heat) gain. Reducing solar gain is an important factor in reducing the environmental impact of high rise developments,” said WSP Building director Gionvani Festa.

“The design for the Shard of Glass in London, UK has a triple skin to overcome the solar gain issue. The outer layer is double glazed and the cavity between the outer and inner layer has built in blinds and mechanical vents.”

The exposed nature of high rise structures can also offer environmental benefits. US-based architect Skidmore, Owings & Merrill's (SOM) design for the 69-storey Pearl River Tower in Guangzhou, China uses the wind and sun as a power source for the structure.

“The Pearl River Tower is designed as a high performance building that is shaped by the sun and wind,” said SOM project design architect Gordon Gill. “The tower will absorb its environment and use it to its advantage.”

The design features solar collectors to provide solar power and heating for the building's hot water supply. Wind will be directed into openings on the mechanical floor to power turbines that will operate the tower's heating, cooling and ventilation systems.

According to SOM, the design also maximises use of natural daylight to reduce energy consumption and will minimise solar gain. In addition, rainwater will be collected for use in the tower's heating, ventilation and air conditioning systems, while the structure will be chilled by a combination of stack venting, radiant slab cooling and caisson heat sinks.

“The trend towards mixed use high rise developments is giving designers greater opportunities to improve environmental performance,” said Mr Slade. “Rejected heat from office areas can be used to heat water for domestic and kitchen use.”

Record breakers

While environmental considerations are starting to shape new designs for high rise developments, the rivalry to have the tallest building still grabs headlines. Taking these iconic structures from design to reality is no easy task and the logistics of constructing these ever taller skyscrapers is presenting the contractors with considerable engineering challenges. The Burj Dubai is no exception.

The final height of the building has yet to be divulged but 18 months into the construction phase of the project, it has already reached 200 m. The construction joint venture of Samsung, Besix and Arabtec is expected to complete the project in late 2008 and is currently forming up to two floors a week.

The reinforced concrete frame which will take the Burj's central core and three wings up to around 575 m in height is being formed using a self climbing formwork system supplied by Doka and specially developed high pressure concrete pumps from Putzmeister. The concrete structure will be topped by a steel frame which will take the tower up to its final height.

Doka worked with the joint venture contractors to design the formwork solution for the project and has split the work into six 'de-linked' zones, which has enabled the work to progress on a three day cycle. More than 180 cycles will be needed to take the concrete structure to its full height and to complete each one around 5000 m² of Doka's Top 50 wall formwork will be lifted on 227 automatic hydraulic climbers.

Concrete for each cycle is delivered to the construction level by two delivery lines connected to two BSA 14000 SHP-D 130 bar pumps developed for the project by Putzmeister. Both of the delivery lines are divided into four legs, each of which is connected to a stationary placing boom that is fixed onto the climbing formwork. Concrete for the central core is also placed by a Putzmeister MX32 boom, which has a 32 m reach.

Full height?

With the Burj Dubai already progressing well and plans for Kuwait's 1 km tall Murbarak Tower under development, is it possible to go any higher? According to WSP's Mr Slade, it is not engineering capability that will limit the height of tall buildings but economic and logistical considerations.

“The number of lifts needed to move people up and down taller buildings takes up considerable space within the core and the lateral systems needed to resist wind loading at great heights also takes up useable floor space,” he said. “We can physically build taller skyscrapers, but whether they are economically viable is another matter.

“Outside factors also influence the ability to go higher. The impact on aviation is a big consideration as is driving foundations capable of supporting the structure – high rises in London are generally limited to 300 m because of the local ground conditions. The ability of the local infrastructure – sewerage, water and electricity – is also beginning to impact on the viability of new high rise developments in some cities.