After water, concrete is the second most used material in the world. The annual production of concrete in industrialized countries amounts to 1.5 to three tonnes per capita and is still increasing. It is also very versatile as a structural medium.
Three highly disparate buildings showcase three very different approaches to the use of concrete which have delivered specific benefits.
The Bella Sky Hotel in Denmark, designed by architects 3XN, features two towers leaning in opposite directions at a gravity-defying 15 degree angle with the top nine floors of tower one and the bottom nine floors of tower two both twisting an additional 19 degrees horizontally.
What makes this all the more exciting and challenging has been creating the building in pre-cast concrete units.
“Abroad, a building such as Bella Hotel would normally be built using in-situ concrete or steel. But in Denmark we have a tradition of using precast concrete units. It is cost-effective, results in fewer flaws in the individual units and is far more comfortable to work with,” said Kaare K.B. Dahl from engineering firm Ramboll. “With such a complex geometry, however, it is quite a challenge to lay this concrete puzzle and assemble the parts into one viable building.”
The project team had to rethink and re-engineer all standard details to reflect the complex geometry and forces needed to create a solution for the 76.5-metre tall towers. All calculations and drawings were extracted from a 3D model. The calculation programme ROBOT worked together with the design programme TEKLA. The combination of these two programmes made it possible to answer crucial engineering questions such as: How will the earth deform when the building settles and how far will the top of the building move sideways in the present conditions?
Every detail was entered into the model, which incorporated all changes into the 2D drawings generated directly from the 3D model.
Park City Musashi Kosugi in Japan, a development by the Takenaka Corporation, is a 59-storey, 200-metre apartment building. Once the tallest residential structure in Japan, the project used FC 150N super strong concrete (with a compressive strength of 150 newtons per square millimeter) for the first time in Japan.
The development of high-strength concrete has been essential in meeting the growing demand for taller buildings in seismic regions. Closely spaced and properly detailed transverse reinforcement provides a stable mechanism for shear resistance and confinement of concrete and longitudinal bars during displacement reversals. Confinement, in turn, increases concrete ductility, controls crack growth and helps maintain member integrity.
Assembled precast concrete members provided a cost-effective solution for the development, enabled easy construction and provided the acceptable static properties as well as adequate dynamic characteristics required for the high seismic zone.
Meanwhile, in Switzerland, the use of concrete at the Centro Ovale in Chiasso potentially shows a different way of thinking about sustainability and future adaptability in buildings.
Sometimes referred to as the ‘silver egg’, the oval structure is self-supporting and surrounded by a concrete shell with 1,024 portholes which offer visitors an unobstructed exterior view and allow abundance of natural light to filter in. The shopping centre is spread out over four levels, with the focal point a central open area that occupies 118,000 square feet of commercial space.
Designed by neue Holzbau AG, this oval shaped timber structure was used to form temporary concrete shuttering for the external shell. High quality precision joinery, forming the shuttering, had to meet the stringent performance requirements set by the concrete engineer. The testing for the geometric accuracy of the framework was carried out using laser scanning.
Apart from being a striking architectural design and an unusual structural form, the outer shell structure has a single primary function – to resist the external environmental loading and provide the “envelope” or “umbrella” structure.
Inside it is a free-standing multi-storey structure which can be modified, removed or replaced without disturbing the outer envelope, to suit changes in future use.
It is certainly an interesting development and showcases both the functional and aesthetic versatility of concrete.