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Sat 20 Feb 2010 04:00 AM

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To infinity and beyond

CW discovers the twists and turns property developer Cayan has faced during the making of Infinity Tower.

CW discovers the twists and turns property developer Cayan has faced during the making of Infinity Tower.

In 1173, the Leaning Tower of Pisa was built with the intention of standing vertically, but its current state is what drives tourists into the Italian district of Tuscany. London's 30 St Mary Axe, nicknamed ‘The Gherkin' for its unusual shape, also attracts the crowds, just like the Kuwait Towers do, with their unique glass spheres.

World famous buildings are often identified by their distinctive silhouettes, and now, Dubai is hoping to create a new icon, with a twist.

Infinity Tower, located in the Dubai Marina, is set apart from its neighbours by its rotating structure and is spiraling into the sky at a fast pace, with one floor being cast every five days. And, when Construction Week went to press, the building reached the 46th floor.

"We are actually ahead of schedule. We allocated seven days to finish a floor but we are doing it in five days," says Ahmad Kasem chief development officer for Cayan, the project client.

"We will complete the structural work by mid June at the latest."

The residential building offers studios, one, two three and four bedroom apartments, as well as duplexes and penthouses. It also has six podium parking levels and amenities such as a swimming pool and retail outlets.

It is set to be topped off at 73 storeys and 305m in height, with the entire development scheduled to be delivered in April next year.

News about a completed ‘icon' will be welcomed during this climate, after the economic crisis caused delays to projects across the GCC. But, for the Infinity Tower, the crisis is a gentle breeze, compared to the severe blow that knocked its construction plans two years ago.

On February 7, 2007, after enabling works had commenced and excavation works were complete, a wall that held back the Dubai Marina was breached. The site was ultimately flooded, leaving only the arm of a crane peaking above the surface of the water.

"The diaphragm wall failed and the whole thing filled to the same level as the marina," Kasem adds.

Apart from physical damages, the flood also scarred the projects finances according to Kasem: "We spent close to AED100 million on dewatering and retrofication works after the incident occurred. This was added to the total construction costs, which now equates to AED1 billion."

As a result, the project was delayed for over a year before construction started up again on June 15, 2008.

Prior to construction commencement and the flooding incident, main contracts and subcontracts were awarded.

In 2005, Skidmore, Owings and Merrill (SOM) won the contract to design the structure, due to its ability to create an unmatched product, according to the client.

"At Cayan, we always want to be different," says Kasem.

"We ran a design competition that included four or five consultants and eventually awarded the contract to SOM. The project is unique and distinguished."

Arabtec won the main construction contract in December 2006, but price escalations later occurred.

"Between 2007 and 2008 material prices went up, which is when we signed the subcontracts. Still to this day, we have very high priced supplies on site," explains Kasem.

"We did a lot of negotiation with our subcontractors and main contractors to reduce costs and we have succeeded in doing so."

The main construction contract is now valued at $209.6 million.

Over a year on, and rapid progress is finally being made on the eye-catching Infinity Tower and Cayan is now confident that the project will be a success.

So, how exactly are the twists and turns in the building's structure created?

In short, each floor, or slab plate, rotates 1.08 degrees around a fixed cylinder core. Once the tower is complete, the 73 floors will add up to a cumulative 90 degree angle.

"The thickness of the core wall is 1m and it tapers down as you get higher. Right now I think it's at around 90cm and it's a fixed structure," says Kasem.

There are no pillars in the building; instead it is supported via a complex concrete column structure that works with the core to hold the building up.

Fast facts

Client:Cayan

Consultant:Khatib and Alami (local), Skidmore Owings and Merril

MEP: Drake and Scull International

Curtain Wall: J & H Emirates

Elevators and vertical transportation: Kone

Tender date: April 2008

Construction start date: June 15, 2008

Contract period: 34 months

Completion date: April 2011

Construction cost: US $209.6 million

Project cost (with remedial works and land cost): US $272.2 million

"The plate is heavily reinforced to take care of the eccentricity of each column as you go up a level," he adds.

Camber formwork was also supplied to the project to counteract the effect of deflection caused by heavy reinforcement and concrete.

"We built the core so it was slightly tilted, so when the slabs were put in place, it was pulled back into a straight line. When you rotate, everything is pulled towards the core," explains Kasem.

The rotation of the slabs and columns are so complex that they need to be checked much more regularly than they would in a traditional building.

"In a normal building, the four corners are monitored every five floors or so. At Infinity, we have hundreds of points that have to be checked every single time we form and are monitored again after the form is taken away. We have to make sure that the columns have been constructed in accordance with the original design."

Cladding work commenced in Q1 2009. In such a complex structure, it should be a difficult process, but Kasem has a trick up his sleeve.

"The cladding is prefabricated in the factory and you just bring it in, slap it on and your done," he says.

"When you have a stick system, you have worry about constructability and workmanship. Two labourers can do something different to the two workers on the other side and there might be problems with sealants and the installation process. With a unitised system, like ours, things are a lot simpler."

Before Infinity's curtain wall could be implemented, however, it had to go through some rather vigorous tests.

"The trouble with a spiral building, is that nobody knows how it will behave, because a building like this hasn't been constructed before. There were a lot of concerns and we want to make sure that the building was over designed, if you will," states Kasem.

A curtain wall prototype was exposed to a typhoon situation, where jets of water were sprayed at it and strong winds were blown on to it using a propelled engine.

"It was proven to be 100% water-tight," says Kasem. "The cladding also underwent pressure, suction and destruction tests. Further, the building has been designed in accordance with the seismic requirements for Dubai."

The shape of the structure has also created challenges for Cayan when it comes to cleaning the tower.

"This was our biggest challenge of all," insists Kasem. "We brought in three top suppliers of the building maintenance unit (BMU) in the world and it took six months to get right."

Unlike on a vertical building, where a cleaner would go straight up and down, he or she has to attach his or herself to each floor and follow the spiral line, according to Kasem.

"You can't just come down the building in a matter of minutes and going back up is a real hassle."

The building takes months to clean and has to be cleaned four times a year. So, in effect, it will be cleaned all year, every year.

Elevators, on the other hand, are not affected by the spiral shape and move up and down at 7m per second inside the core of the tower.

Another obvious concern for Cayan is on site safety and security, and the company is keen to reiterate the importance of such issues to its workers.

"We will not allow anybody to smoke on site and anybody that goes onto our site, no matter who it is, will not be allowed to enter without hard hats and safety shoes etc."

Cayan and Arabtec carry out weekly safety reports and take note of any incident that occurs before finding out why it happened and how to prevent it from happening again. Further, safety meetings with workers are carried out regularly.

So far, there have been seven lost time injuries during the 3.7 million man hours worked on site.

So what's next on the agenda for the Infinity Tower?

The coming months will see the completion of structural and cladding work at infinity tower, and interior fit outs will follow.

"Just imagine putting the Grosvenor House on top of infinity as it stands now and that is how much more work we have left to complete," says Kasem.

With the trials and tribulations the tower has been through so far, however, constructing a few extra floors shouldn't be too strenuous for the Infinity team.

Ross Wimer, of architecture firm Skidmore, Owings & Merrill, is the design partner for Infinity Tower. CW chatted with him about the distinctive design. What inspired you to create the rotating structure?

The shape of the Infinity Tower is twisted to maximize the views out of the building. At the lower floors there are more units oriented toward the Dubai Marina, near the top of the tower they face the Arabian Gulf.

What seismic provisions have been implemented? If this is a unique structure, how do you know that it will resist ground movement and strong winds?

Our design for the tower structure is based on over 75 years of engineering experience. As with all of our high rise designs, it was tested both in computer models and in a wind tunnel. One thing we discovered in the testing is that the twisted shape performs better in the wind than a rectangular extrusion of the same proportions.

What challenges did you face when designing this building?

One of the challenges was to keep the geometry of the condominiums as regular as possible, in spite of the tower's external shape, and to be sure that the tower could be built quickly and efficiently. We achieved this by stepping the structure of the tower and designing the framing, so that the same formwork can be used for all of the floors in the building. The formwork is simply rotated about one degree at each successive floor level.

Have alterations been made to the design over the last couple of years?

The tower design has remained unchanged, relative to our original plans. The podium building has been adjusted slightly to allow for additional parking spaces.

How would you compare the Infinity Tower to your Burj Khalifa project?

The Burj is a achievement by virtue of its remarkable height. The Infinity tower represents a new trend in tall building design where sculptural shapes are now possible.