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Lotus on legs

Major design and construction challenges must be tackled to build Singapore's new Marina Bay Sands integrated resort. Report by Adrian Greeman.

For 50 years, Singapore has been constantly under construction, creating, from the once British colonial outpost, a futuristic city of high-rise offices and hotels with a dense infrastructure of housing, a high-grade metro network, underground and overground freeways and one of the world's best airports.

Its latest project is the most ambitious yet, a £2bn complex of arts and exhibition facilities, three extraordinary curving 50-storey high hotels with over 3,000 rooms, and leisure and shopping on a grand scale. The whole development is sited at the central focal point of the city, the Marina Bay.

The 20ha integrated facility includes reconfigurable waterside performance areas, two enclosed theatres, two transparent "crystal pavilions" in the water accessed by undersea tunnels, a giant exhibition and conference centre, Asia's largest ballroom and, finally, a large casino, one of only two in Singapore.

The latter is included as part of a deal with the project's backer, Las Vegas Sands Corporation. It owns a giant integrated complex there and has already moved outwards from its Nevada base with another huge development in Macao. It sees Singapore as the next step into Asia.

United States architect Moshe Safdie Associates and local firm Aedas won a large international competition for the project, primarily because their proposal satisfied Singapore's wish to build a major cultural facility and an iconic building at the centre of the city. The lotus-shaped ArtScience museum at the tip of the scheme's long three-storey podium platform houses the retail and restaurant areas. The structure is one of the main challenges for engineer and consultant Arup.

Click here for diagram of conference centres & casion foundations

Another part of the project is the Sky Park. It is an extraordinary concept, a green space 200m in the air spanning the tops of three hotel buildings and projecting a further 60m at one end.

Trees and garden plants will landscape the space alongside a 170m-long swimming pool and a series of bars and restaurants. A public viewing platform will give views to neighbouring Malaysia and to surrounding Indonesian islands.

The hotels, two five-star and one four-star, are shaped like Chinese characters, with splay legs coming together at the midpoint and then diverging again, and a different leg spacing and footprint for each. Through the legs, and again linking the three hotels, runs a continuous atrium 19 stories high with a sloping roof beam from the farthest hotel downwards.

The civil and structural engineering for the project is one of a series of challenges for Arup, says the firm's Singapore director Cheong Va-Chan. "It is very long and high with a series of trusses needed to run the length of the atrium, which is over 50m tall," he explains. Vertical trusses link this top element to the ground.

Though complicated, he says it is not the biggest challenge structurally. More complex are the structures for the three major public facilities – the exhibition and conference space, the casino in the middle, and the two theatres at the seaward end, sitting together in a third building. Each of these has a curving form, half convex and half concave, changing direction at a central diagonal spine.

"There are approximately 80m diagonal trusses needed for those with perpendicular connectors to the columns at the side. That is made more complex because the connections are not precisely right angles."

The total size of the covered space is 220m by 110m, and the spines have just a single intermediate support. Floor grids for the buildings use 33m span trusses, "which is enormous," adds Cheong. "We were using only 18m in Macao." But these complexities are a relatively insignificant "piece of cake", he explains,
compared with the two major elements of the "lotus" building and the Skypark.

The Skypark sits on a steel platform supported 12m above the three concrete hotel towers by a cluster of angled steel legs. Most difficult of all was creating the cantilevers, says Cheong. Critical aspects were not only the loads but the vibration effects. Wind also had to be considered, and major wind-tunnel tests were run in Canada.

Click here for diagram of Marina Bay Sands Skypark Scheme

Truss forms were examined, but in the end 10m-deep box girders linked by cross pieces were used. "It took a year to resolve many of the issues," he says. Doing so drew on the latest software and 3D modelling packages, such as Bentley Structures and a number of programmes developed by Arup on Beijing Olympics buildings – for example, the Olympic swimming pool's external 'bubble' walls. Arup drew on the expertise from projects in Hong Kong, Australia and London to supplement the efforts of the 3D modelling team built up in Singapore.

In charge of modelling was Chris Pynn, a CAD specialist who says the scheme has given the Singapore office the chance to develop a skilled team of 26, mostly with 3D skills. "We started with one person," he explains. The team has gone directly from the architect's RHINO 3D model into its own packages, including structural optimisation programme GSA. Information has been supplied direct to the contractor in 3D format and the team has also produced millimetre-accurate fabrication details for steel fabricators.

Hardest of all the analyses was the ArtScience building's lotus-shaped steel frame. However, using software scripting it was possible to analyse this one petal at a time, altering the parameters for each subsequent part. "The main system is a diagrid sitting off the basement's three slabs and taking the lateral load," says Pynn.

Meanwhile on site, the huge construction effort is in full stride. Foundations for the project are on a massive scale, not least because it sits on a reclaimed area of Marina Bay, where the notorious local marine clay characterises the ground conditions. This is a gooey toothpaste-like mush around 12m deep. Much of it has been extracted to make way for the large underground car-parks underneath the facility.

As in many areas of Singapore, it is necessary to go down to over 50m with large bored piles up to 2.8m in diameter for the halls and 3m by 1.7m barettes for the hotels. Larger piles were planned, but the piling equipment needed is scarce in the region.

This work is being done by Bachy Soletanche with local firms L&M and Sembo. They are working inside four huge circular diaphragm walls 1.2m thick and 130m across beneath the main halls. The hotel rings are just 90m across. "These are allow strut-free construction for much of the site" says Cheong.

Another major challenge will be erection of the hotel frames which have sloping shapes that do not meet and mutually support each other until they are over 20 stories high. Contractors will use struts and temporary post-tensioning to keep the towers in place as they rise.

Project and construction management is done directly by a 250-strong team of Marina Bay Sands' staff and consultants.

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