Shaped Concrete Boards with Skylights
A signature architectural marvel of the spectacular new building at the Museum Städel in Frankfurt am Main is a large underground exhibition hall with a remarkably shaped ceiling. The visitors have a view over a magnificent meadow with 195 round skylights, which let the daylight into the underground hall. By night, the lighting of the exhibition hall shines outward through the skylights. For this impressive engineering fete in ceiling design, ACCENTform made the concrete formwork girders.
To concrete the ceiling of approximately 3,000m² (3,688 yds²) large exhibition hall in a three-dimensional geometric shape, the concrete formwork girders were required. To accomplish this, negative molds reproduced the free-form surface. ACCENTform manufactured 195 shuttering boards. The huge ceiling area with the immense differences in height was a tremendous challenge for all persons involved. Therefore, the lead construction company (Ed. Züblin AG) decided to concrete the ceiling in five sections: four rectangular sections (each of them covered a corner of the exhibition hall), and a fifth section, which due to its special hill design took the central area. Efficient and professional: The division into these five concrete sections ensured the reusing of the formwork beams up to four times. Another important criteria in the production of concrete formwork beams, consisting of a shaped upper construction and a standard subconstruction, were budget-friendly square metre prices along with a high level of shape precision and smooth and pressure-resistant surfaces.
To the Production of Formwork Beams
The substructure consisted of a 2 cm (0.8 in) thick three-ply shuttering panel that was reinforced with 10 formwork girders (type VT20). Then, the CNC-machined PS rigid foam blocks (Styrofoam) were glued onto these reinforced panels. The use of PS hardened foam ensures not only price advantages over other materials, but, due to its high compressive strength (200 kPa); it also guarantees a visible success in the ceiling design. Moreover, the employment of a robot (KUKA KR 150) by the CNC milling of the three-dimensional surface proved to yield highly economical results.
In order to ensure a good quality of strong concrete and at the same time to guarantee a high compressive strength of the surface, the PS rigid foam had to be sealed professionally. For this purpose, an approximately 5 mm (0.2 in) thick fibreglass laminate was applied. Subsequently it was smoothed and sealed with a topcoat. This method ensures a reproducible smooth surface for all further shuttering oil treatments.