A glimpse of the dream - at last

Nigel Clifford, the senior project manager, in front of the Sheikh Zayed Bridge as it enters into the last few months of construction.

The world's 'most difficult bridge' is finally emerging from a tangle of scaffolding, concrete and steel in the Maqta Channel. This unique engineering challenge will be a thing of outstanding beauty but getting there has taken nearly 20 years. ABU DHABI // Almost two decades after it was proposed, 10 years after it took shape on the drawing board and six after work began on the ground, the bridge that planners say will be the most beautiful gateway to the island of Abu Dhabi is finally taking spectacular shape.

When it opens, the Sheikh Zayed Bridge, already being described as the "most difficult bridge ever built", will span the Maqta Channel alongside the bridges of Al Maqta and Al Musaffah, which currently carry all traffic in and out of the capital. It is due to open in December and is certain to attract worldwide attention. "We wanted to make a bridge that would stand out from the crowd and would be instantly recognisable," said Abdullah al Shamsi, the director of roads and infrastructure at Abu Dhabi Municipality.

"Just as the Golden Gate bridge is synonymous with San Francisco and the Sydney Harbour Bridge with Sydney, we want to create an icon for Abu Dhabi." The bridge is already three years behind schedule, but the wait, he said, would be well worth it: "Any project on this scale has a risk of overrunning, but that is the price you pay when you want to create something monumental." The man charged with turning this ambitious dream into a reality is Nigel Clifford, the resident engineer from the British construction-management consultants High-Point Rendel. Squinting into the sunlight, he toured the site - still a tangle of scaffolding, concrete and steel - and pointed out the key features of the project.

"It is a very complex structure made of a series of geometric shapes," he said. "It is only symmetrical in one dimension: along the length of the bridge. There is no repetition, which is unusual in a project like this, so it takes a lot longer because each part has to be fabricated individually." He relishes the challenge: "Architects are there to come up with interesting and inspiring designs. It's the engineers' job to turn those designs into something that can work."

The idea of constructing a new bridge was first floated by the Abu Dhabi Public Works Department 18 years ago, but the original designs failed to catch the imagination of the city planners, who wanted an awe-inspiring structure that would put Abu Dhabi on the map. In 1997 they invited the Iraqi-born British architect Zaha Hadid, a rising star in the architecture world who had already won awards in London and Hong Kong for her inspirational work, to tackle the project.

The planners wanted a bridge that would simultaneously symbolise the nation's future and pay tribute to its past. Ms Hadid proposed two concepts, one based on a zigzag pattern and the other reminiscent of the undulating profile of sand dunes. It was the latter design - an ambitious vision of sleek curves echoing the low, rolling desert landscape that dominated the skyline when the UAE was born 38 years ago - that was selected and won Ms Hadid the job.

The choice of architect proved to be inspired; Ms Hadid has continued to push the boundaries of conventional architecture around the world. In 2004 she became the first woman to be named laureate in the 26-year history of the prestigious Pritzker Architecture Prize and last year she was ranked at 69 in the Forbes list of the world's most powerful women. One of the Pritzker jurors was Frank Gehry, the 1989 laureate and the architect behind the Guggenheim museum that will be built on Saadiyat Island in Abu Dhabi. "The 2004 laureate is probably one of the youngest laureates and has one of the clearest architectural trajectories we've seen in many years," he commented when Ms Hadid won the prize. Each of her projects, he said, "unfolds with new excitement and innovation".

Mr Gehry and Ms Hadid have the Guggenheim brand in common; in 2004 she was asked to design an outpost of the museum in Taichung, Taiwan. Her other work includes the Mind Zone for the Millennium Dome in Greenwich, London, in 1999 and a ski jump in Innsbruck, Austria, in 2001. Sheikh Zayed Bridge, she says, "was a very exciting project to get involved in. The idea was based on replicating the sand dune formation but as a structure. The inspiration came from the region and the Middle East in general.

"The clients wanted a design that would encapsulate seamlessness and fluidity; a structure that would be both elegant and practical and also pioneering. Architecture is all about design, engineering and elegance." Over recent weeks, drivers who regularly cross Al Maqta may have noticed a sudden burst of progress on the new bridge, to their right as they enter the city, and a sense of its shape and the impact it will have when complete is beginning to emerge.

The bridge is composed of three main arches, made of steel and mounted on concrete supports. The arches and cables support two four-lane carriageways, an emergency lane and a pedestrian walkway, running through and alongside the roller-coaster framework. It is a mark of Abu Dhabi's rapidly accelerating expansion that when the bridge was originally designed it featured only two lanes in each direction; as the city's population expanded, so planners realised they needed to double its capacity and the design was amended accordingly.

Although the Maqta Channel is only 150m wide, the bridge will be 850m long, with the arch of the central span soaring to 63m - more than two-thirds of the height of the nearby Sheikh Zayed Grand Mosque. The climate of the UAE presents problems for builders working with steel and the bridge comes complete with a specially designed dehumidification plant that will circulate dry air through the hollow concrete supports and steel arches to combat corrosion.

And the design itself has proved demanding for those charged with executing it; an architect's inspirational and boundary-pushing design can become an engineer's construction headache. "I would say this is the most difficult bridge ever built," Mike Davies, assistant resident engineer at High-Point Rendel, said in a recent interview with New Civil Engineer magazine. "Nothing about the bridge is regular; all the spans are supported differently; every piece is specifically designed and engineered. It is all one-off stuff."

This complexity, according to Ms Hadid, "comes from combining the artistic with the engineering practicalities". Work on the project began in 2003 and the bridge was initially due to be completed by 2006; three years later, however, the job is still far from over and, despite the burst of progress, construction teams will be hard-pressed to bring it in on time for the current deadline of December this year.

Meanwhile, costs have soared. The Dh635 million (US$172m) price tag was based on the original construction timetable of three years and, while no official figures are available, industry experts estimate the current cost to be between Dh800m and Dh1 billion. Mr Clifford commands an army of hundreds of labourers, including teams that work throughout the night. "We have around 600 or 700 workers involved in the project during peak times, both here on site and constructing the temporary works needed to erect the arches," he says.

About 15,000 tonnes of steel were used to make these temporary works - the scaffolding and supports needed to raise and weld the arches into place. Barges are used to manoeuvre cranes and other heavy gear into place on the water. The bridge is only one part of a citywide master plan to ease the worsening traffic problems and will connect to the eastern Corniche and Al Salam Street, reinvented as an eight-lane motorway along which drivers will be able to travel into the heart of the city without encountering a single traffic light.

This development, which is scheduled to take two years and cost Dh620m, is dwarfed by an even larger project to construct a 3.2km eight-lane tunnel from Al Falah Street to Al Meena Road. This is due to be completed by October next year and is expected to cost Dh3.1bn. [e-mail]