LIGHT AND DELICATE
A bus stop canopy made of ultra-high-strength concrete.
The Parapluie is an architecturally sophisticated, highly innovative concrete shell structure designed for the series production of bus stop roofs. The realisation of this filigree, only 25mm-thick structure made of ultra-high-strength concrete by DUCON with multi-layer micromat reinforcement was achieved by means of a high-precision mould construction by ACCENTFORM.
For the engineering achievement, the authors involved received the Tsuboi Award 2013 for their outstanding script at the 2013 IASS Symposium: Philipp Eisenbach (Bollinger + Grohmann), Ragunath Vasudevan (schneider+schumacher), Manfred Grohmann, Klaus Bollinger and Stephan Hauser (DUCON).
A parametric form-finding process was used to develop a system that transfers the loads of the shell via membrane effects. The result of intensive research, development and testing is a concrete shell that, with an edge thickness of less than 25 mm, is as light as it is resilient.
Only the outstanding engineering performance of the participating offices in combination with the implementation by experts like ACCENTFORM could make such a project possible.
ACCENTFORM’s way to the perfect mould – in four steps
1. since extremely stable and cost-effective moulds are required for the production of economical concrete formwork beams, a stable wooden substructure (made of glue beams) with a cover plate is first manufactured. This substructure enables a reproducible chip support during the subsequent milling and leads to an even and safe load transfer during the actual concreting.
2. large-volume STYROPOR blocks are then glued onto the timber substructure. The cost-effective STYROPOR blocks fill the space in between up to the actual functional surface.
3. the STYROPOR structure is pre-milled with undersize and then coated with a Bepastung or PU hard coating. This creates a hard surface that ensures high compressive strength.
4. to maintain the exact surface geometry, the coating must be milled a second time. The resulting surface is finely sanded manually and finally lacquered. An additional polish can also be used to achieve high-gloss surfaces.
The combination of ACCENTFORM’s precision in mould construction with the design and engineering services of the participating offices, as well as DUCON’s special material, opens up countless other possibilities for producing ultra-thin concrete shells through parametric shape optimisation. With the help of the high-performance and micro-reinforced concrete, extremely thin and equally load-bearing structures can be realised, be it for furniture, ceilings or façades. Engineers and architects alike can benefit from this when they are looking for technically feasible innovative forms.