Leaning at a gravity-defying 15 degree angle, Bella Sky Hotel in Copenhagen’s Ørestad offers a sight never seen before: Two towers leaning in opposite directions at an angle almost four times that of the leaning tower of Pisa. The geometrical dare continues as the top nine floors of tower one and the bottom nine floors of tower two both twist an additional 19 degrees horizontally.
The two towers lean 15 degrees to each side. They are 76.5 meters tall with a total of 814 rooms and a building area of 44,173m2. To erect this landmark structure in Ørestad without errors requires innovative thinking. The forces in play at Bella Hotel are enormous. As a consequence the project team had to rethink and reengineer all standard details to reflect the complex geometry and forces. Ramboll participated in the project as consulting engineer on structures, sewers and earthworks. The building was completed in the beginning of 2011 in cooperation with the architects from 3xN.
Concrete geometry
"One of the most exciting things about the project has been to create a building which is so twisted and with such a complex geometry in precast concrete units," Kaare K.B. Dahl explains. "Abroad, a building such as Bella Hotel would normally be built using in-situ concrete or steel. But in Denmark we have a tradition for using precast concrete units. It is cost-effective, results in fewer flaws in the individual units and is far more comfortable to work with. With such a complex geometry, however, it is quite a challenge to lay this concrete puzzle and assemble the parts into one viable building."
3D model for calculations and drawings
All calculations and drawings used by Ramboll on the project 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 calculate things such as: How will the earth deform when the building settles? 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.
"One of our biggest challenges was to grasp and handle the very complex geometry and to do this TEKLA has proved invaluable" Kaare K.B. Dahl explains.
