Confuse the wind

SOM discovered that the little blades on the spire also help to confuse the wind even up there. (XAVIER WILSON)

The journey from an initial meeting in 2003 with developer Emaar Properties to today's opening of the Burj Dubai has been long and challenging for Skidmore, Owings & Merrill (SOM). The 75-year-old international architecture, interior design, engineering and urban planning firm that designed the world's tallest building has seen many changes in planned heights and building function, upheaval in the global market and highs and lows in building material prices.

And the story of how the company made sure the design intent was translated into the slender, iconic landmark that now pierces the sky above Dubai is one that many would like to hear, particularly as many tall buildings are designed but never get off the drawing board.

"The final setting of a date for the Burj Dubai opening is exciting but also very sad," said George Efstathiou, Managing Partner at SOM's Chicago office. "I first met Emaar in March 2003 at an interview before the competition in New York. People have come and gone but there has been a lot of stability in our team.

"It has been close to seven years that we have been working with Emaar. The initial stages were very exciting. Nobody knew where we were going because the initial design competition was for a 550-metre tower. Soon after that we were appointed and fees were negotiated but we then realised that there were discussions about us going taller and bigger.

"Those were very exciting times and that took a year to sort out. The next year went into documenting the design and engineering the building (see timeline on page 21). We designed the Burj Dubai and every inch of the interior space, which is about 2.4 million sq ft of interior design in the building, with the exception of the Armani Hotel and the observatory.

"Now, we are in the finishing stages of trying to wrap up things with the project team. It is an exciting time and yet I feel sad because we can see the end of the project in terms of our participation. When it comes to tall buildings, we have a history of sticking with our buildings and helping the clients (eg the John Hancock Tower)." At a previous meeting many years ago, Efstathiou said the area around the building would pay in the long run for the costs of the building.

"The initial design and vision for the building was that it would become the centrepiece of the Burj Dubai master plan. That building itself was the catalyst for the rest of the development. What happened is that the Burj Dubai, as planned, created value around it.

"Apartment buildings as well as the rooms of the Address Hotel that faces the Burj Dubai are much sought-after. The master plan has met all the goals the client had at the beginning."

More important than the design is the structure. And the kind of detailing that goes into that aspect will dictate the life of the building, starting with corrosion control.

Bill Baker, Partner in charge of Structural and Civil Engineering at SOM, said: "It is very well known that in the Gulf the groundwater is very corrosive and has more salt than seawater. Therefore, Dubai has developed a very good concrete industry to counteract this situation with a very high-quality concrete.

"With this project we wanted to go beyond the norm and therefore the rebars have cathodic protection to reverse the way the electrons flow so the steel won't rust. We also used very high level concrete with low porosity so that the ground water won't get it and we made it extra thick."

The practice also paid special attention to the seismic studies, mainly for the podium

and spire. "Most of the building is controlled by the wind," added Baker. "But at the very top during an earthquake there is a whipping action and that affects the steelwork. The podium does not have any wind force but there is a lot of weight from the concrete. So an earthquake would excite the concrete slabs.

"That is why the low-rise is much more controlled. Even when you have high-frequency and very quick movements, the tower is flexible and very long so it really never gets excited. But the low-rise's natural frequencies are much tighter and therefore it tries to keep up with the ground motions of the earthquake and generates higher forces. Dubai is fairly mild seismically. So we commissioned special studies to see how accurate that was and used the Dubai code, which is conservative."

The geometry works well for the architecture and for the structure too, he said.

"The building is residential with an office tower and a hotel so we needed something that could be spread out. We have developed a similar system in the past and so what we have here is a central core in the middle, which acts like an axle to keep the building from twisting.

"The second core was too slender to go to very great heights and it needed to be stiffened. We decided to use the corridor walls and the cross walls between the units to buttress the center core. It is like a marriage of a pipe in the middle and three I beams being tied together. The Y-plan is common for hotels and residences and ensures that you have lot of units without residents looking into their neighbours' rooms."

In terms of the mechanical, electrical and plumbing (MEP) aspects, Baker said SOM had carried out its own internal studies.

"Hyder Consulting did not get involved till later. The MEP is like Swiss watches since there are so many floors. Everything has to be laid out very efficiently because if you waste any area then you have wasted it 160 times. The concrete is also very strong so we spent a lot of time co-ordinating the MEP so that you don't have to fit it later."

So how did the firm handle the changes in the heights?

"When we first won the competition in March and started work in April or May 2003, it was only 10m taller than Taipei 101. The client kept changing the brief and increasing the area. We kept getting wind tunnel data and stretching the height and did not know how high that would go.

"The change in the shape of the building also changed the way the building moves in the wind and we were able to go much higher than we thought we could."

Baker is known for his comment that the design was intended "to confuse the wind".

"If the wind gets very organised you would get very large forces – so large that the building would not be able to be so tall. But by changing the shape many times as you go up, the wind does not get very organised and the forces are reduced to a remarkable extent."

These changes also affected the elevator system, which had to be redesigned.

"Yes, it is an interesting change. Initially the building was residential all the way up. Then the client decided there was a market for very high-end offices – boutique offices – so we had a separate elevator for the offices.

"Then again, with existing technology, none of the elevators could go all the way to the top. So we had to have transfers at least once. The other thing is that tall buildings act like chimneys and so by interrupting the shafts, we were able to break up some of that air."

It all has to make economic sense, he adds.

"What sets super-tall buildings apart from any other buildings is the structure. Cost is important but speed is also important and you have to have a system that has to be built quickly. Essentially, we came up with a system that could act like a vertical factory. So the Burj Dubai went up very quickly because the system is very organised and based on a regular module."

He believes future trends will include a continuation of the industrialisation on sites.

"What you have is a concrete building and what happens is you have the shuttering of the vertical formwork that helps to shape the concrete and that could raise itself up and climb the building. And then we would pump the concrete from the bottom and the only thing that we would need to bring up from the ground was the reinforcement steel or the rebar. It was like a vertical factory and we went up on the deck and it was like visiting a factory."

The spire is different from other spires on buildings around the world.

"It is very tall and slender. But the one thing to notice is a series of little bars or blades that come off the side. We did a series of special wind tunnelling studies and determined how the wind would interface with the top and we did not want it to make the spire vibrate. We also discovered that the little blades at the top also help to confuse the wind even up there."

Eric Tomich, Associate Director at SOM and resident architect, was busy discovering the ground realities of translating design intent into a building.

"We wanted someone to follow it through construction and we wanted to make sure that every aspect of the design intent was followed through, being an international firm and with our expertise in high-rise," he said.

"I started in October 2004 and we had designed quite a bit of the superstructure by then and had already finished with the foundations and piling. The main contractor was yet to be chosen. From 2004 to 2009, the project faced various challenges – including the cladding company going bankrupt.

"Every time something came up, we took it as a problem-solving exercise. We were very lucky with the replacement for the cladding manufacturer. It was very difficult but we finally found Far East, from Hong Kong, who had tendered for the original contract and did not win then.

"So we went back to them and discussed it and found a way to get them involved and the advantage was that we had already worked with them on other projects in Asia. It was a pretty good match for us. They were also locally partnered with Arabian Aluminium."

When SOM won the design competition, it agreed with Emaar to produce the construction documents.

"A lot was built exactly as we designed it," said Tomich. "We did all the design and Hyder came in as a supervising consultation. Its role was to get Dubai Municipality approval and work with the contractor on a daily basis as it was built. Our role was architectural, structural and MEP items as well as the interior design.

"We were very careful to use systems and technologies that were known to work. We built the tallest building in the world and used high-performance systems, materials and detailing that work in a very challenging environment."

One of the biggest challenges was maintaining communication.

"When you build a project like this, it is very important that when you communicate to someone that decision goes right down the line and everyone understands what direction the project is meant to go. At the end of the project, we had 12,000 people on site every day.

"It was a communication challenge to keep them organised, directed and focused since you needed to channel the energies and intelligence. Especially, the co-ordination of all these different brains together in as efficient manner as possible is always the most challenging aspect of large projects."

He had to adopt a hands-on approach to building.

"There is a lot of ground from design drawings to fabrication drawings. Contractors need a lot of guidance to do the work and we had a lot of work to do the work. We hand selected all the stone materials for all the interior spaces [residential spaces and lobby] and worked with different craftsmen.

"We did the same with the rosewood veneer and went to Brazil twice to select the material. We had a crucial role in design execution to preserve and protect the design – we had to be there with them working everyday and it was very enjoyable to work with so many different people."


Lessons learnt: SOM

Efstathiou: "There were some lessons learnt about when to use a local contractor and when to use international contractors and suppliers. That is always the place where you can do better, not just with the Burj Dubai but in any project."

Baker: "We discovered that we had created a new structural system that enabled us to go so high. We also learnt a lot about the scale – we had to understand how to change the building so that it did not look huge. We also had to learn a great deal about wind engineering and construction technology. Samsung, Besix and Arabtec JV did an excellent job in preplanning and coordinating so that the job went very smoothly. The best thing that an engineer can say about a contractor is that the project was uneventful. It was like virtually no surprises.

We also learnt that we can go much higher. We can do a taller building much faster now with the same cost that we have finished with at the Burj Dubai and learned so much. The innovations are secrets and we have some definite ideas that we are going to keep that to ourselves right now. The single biggest challenge was understanding the wind and how we can design for the wind."

Tomich: "The cranes were a very challenging aspect of the project – the logistics and the timings. Especially, when the cranes came down, it was a very sophisticated process and went very well. They were mounted on the building and as the building rose, the three cranes rose with it. The contractor came up with a fabrication yard, where they assembled all the reinforcing bars and cages on the ground into sections. They did all the wiring together of the bars with big teams on the ground and then they would hoist the completed bars way up to the top of the building and into the formwork in time for each pour. Those in turn would be wired up at the top and then they would pour the concrete. By doing this, they got the cycle of the concrete to three days per floor and that is very fast because they took a lot of labour off the top of the tower, spread it out on the ground and then would bring the products up to the job preassembled – a very efficient way to work."


PROJECT TEAM CLIENT EMAAR

Architects and Engineers: Skidmore, Owings and Merrill (SOM).

Design Architect: Adrian Smith, who worked with SOM until 2006.

Supervision Consultant, Design Adoption Consultant Engineer of Record and Architect of Record: Hyder

Construction: Joint-venture comprising Samsung Engineering & Construction, Besix and Arabtec Construction.

Project Manager: Turner Construction

Independent verification and testing agency: GHD

Wind consultant: Rowan Williams Davies & Irwin Inc (RWDI)

Piling: Bauer Spezialtiefbau with Middle East Foundations (UAE)

Formwork for core and walls: Doka Schalungstechnik GmbH,

Concrete: Universal Concrete Products Ltd Co (Unimix)

Elevator engineering: OTIS and Lerch, Bates and Associates Incorporated

 

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