Spherical bearings for the garden above Singapore
Destined to become the new foreground to Singapore’s skyline, a complex consisting of hotel, museum and congress centre is currently being erected which has the dimensions to become a new symbol of this Asian metropolis. The real eye-catchers are the three 200 m hotel towers which will be topped by a huge garden platform measuring 345 x 36 m. In order to guarantee this garden the essential horizontal "freedom of displacement”, it rests on 17 spherical bearings. A tuned mass damper system takes care of the vertically acting vibrations of the cantilevered part of the garden. The bearings and tuned mass dampers are being manufactured in Munich, at the Maurer Söhne works.
"Marina Bay Sands” – promising to act as a future tourist magnet – is currently rising above the Marina Bay Waterfront. The owners of this venture, the Las Vegas Sands Corporation, hope they will have created nothing less than a landmark by the end of 2009. This spectacular complex is designed to house a casino in Las Vegas style, a theatre, a shopping centre, an art museum, congress facilities for up to 45 000 participants, restaurants, night clubs and a luxury hotel with more than 2600 rooms.
The art museum will be positioned like an oversized lotus blossom alongside the beach promenade, and behind that the three 55-storey hotel towers will rise skywards. The absolute highlight will be the so-called Sky Park linking the three hotel towers. The park will have a total area of one hectare and will include restaurants, bars, a swimming pool and a 360° view of the harbour and skyline of Singapore. On plan it will be shaped like a crescent and will cantilever well beyond one side of the three hotel towers.
The park rests on three huge steel platforms, one on top of each hotel tower. Two invisible joints separate these steel platforms. This design poses great challenges for the bearings and the tuned mass dampers. Maurer was awarded the contract by Japanese contractor JFE, who was already familiar the technological and manufacturing expertise of the Munich-based steel construction company from an earlier project.
Challenges for the bearing design
MSM® Spherical Bearings are distinguished by their long service life and high safety against failure, which are key criteria here, considering Sky Park's extraordinarily exposed position. In other words, replacing the bearings would amount to a supremely expensive and complicated task. To that end, a warranty of five years had to be granted, and the lifetime is designed to be at least 50 years. This major challenge for the design of the bearings is due to four factors: the high vertical loads, the high temperatures, the high sliding displacements and the installation conditions during construction.
High vertical loads
The three steel platforms mentioned above support gardens, trees, restaurants and a swimming pool – in short, the luxury to enjoy the skyline of Singapore – and thus result in enormous vertical loads of between 15 100 and 87 100 kN. Therefore, the sliding material MSM® (Maurer Sliding Material) is the material of choice, able to carry extremely high loads like no other comparable material and thus enabling a very compact bearing design. This adds an economical aspect to the bearings, and due to the relatively small footprint, allows the architect creative degrees of freedom.
Furthermore, MSM® copes with the very high temperatures and high moisture levels of Marina Bay. The sliding material is approved for temperatures up to 70°C and therefore is ideally suited for use in Singapore.
High sliding displacements
The key criteria for the use of MSM®, however, were the high sliding displacements and their accumulated displacements over time. The bearings have to accommodate displacements of up to ±1000 mm. The main cause of these high displacements is wind, which moves the hotel towers and the Sky Park or creates vibrations. But the bearings are designed to handle displacements caused by earthquakes, too. In this respect it is important to know that MSM® not only accommodates high sliding displacements and vertical loads, but also the high sliding velocities that occur during earthquakes.
Some bearings are laterally guided, some permit free displacements. Spherical bearings with diameters of up to 1110 mm and sliding plates with dimensions of up to 2850 mm are being installed.
Tuned mass dampers at the tip of the garden
The garden platform cantilevers some 65 m beyond the northern hotel tower. In order to reduce the vibrations caused by wind, rain or persons on the platform, a tuned mass damper system with a mass of 5 t is being integrated into the steel plates. Because the frequency of vibration cannot be easily calculated, a range between 0.8 Hz and 1.2 Hz is being allowed for and the system will be delivered to Singapore with a variety of spring sets. After installation, measurements will be carried out and the appropriate spring set will be fitted as required. In addition, rubber plates above and below limit extreme movements of the damper; these, too, can be adjusted if necessary.
The installation of the spherical bearings represents a further challenge. Maurer Söhne developed an installation unit that allows the bearings to be positioned during the construction of the three hotel towers, but to be rotated horizontally through 90° when the scaffolding is taken down. Because a part of the sliding plate of each bearing is so long that it extends into the sliding joint. Installation in their final position could therefore have been accomplished only after removal of the scaffolding, which would have been very time-consuming. By way of the rotational installation unit, Maurer Söhne could contribute to saving several weeks of construction time.