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From Structural Purity to Site Specificity
New Canopies for the Entrance Gates of the Messe Frankfurt
Agnes Weilandt and Oliver Tessmann
Abstract This paper describes a structural design approach that seeks to replace structural purity and preconceived typologies by site-specific constructions. The process is exemplified by a canopy design for the Messe Frankfurt (Frankfurt fair). The competition-winning proposal is the result of a collaborative design effort of architects and structural engineers. In a computational design process the structure is optimised in regards to fabrication requirements and material consumption. Beyond the particular project, the design process is accompanied by a design-tool development. Shortcomings in existing tools became obvious in the process and showed the need for in-house development of advanced collaborative digital design tools.
Agnes Weilandt
Bollinger + Grohmann Ingenieure, Frankfurt am Main, Germany
Fachhochschule Frankfurt, Frankfurt am Main, Germany
Oliver Tessmann
School of Architecture KTH–ABE, Stockholm, Sweden
1 Introduction
The here described canopy is part of an ongoing project-based research that seeks to challenge structural typologies inherited from modernist practice and nineteenth century design procedures still prevalent in our built environment. In a series of projects we questioned structural system purity, which is often favoured by engineers for the sake of repetitive detailing and simple analysis, but neglects the architectural design approach and site-specific requirements. Our aim, in contrast, is to look forward and design both novel structural systems and the necessary computational tools and procedures (Bollinger et al., 2008).
System homogeneity is useful in vast structures with mono-functional infrastructural use and large spans (Billington, 1985). Migrating structural purity from the mono-functional into the complexity of architecture might, however, prohibit a dialogue between the load bearing and the space forming.
The canopy is one of several projects in which the purity of a structural typology went through a computationally driven evolution and alteration beyond structural optimisation. All projects have in common that their structure is not a superimposed preconceived typology but the result of a negotiation process balancing multiple criteria. The aim is to embrace further programmatic, formal and architectural considerations into the design of structures.
The history of projects is accompanied by the ongoing development of digital design tools. Available tools and procedures have a major impact on how we design. Bollinger + Grohmann Ingenieure constantly urges for close collaborations of architects and structural designers and therefore develops tools for seamless data flow between generation and analysis (Preisinger, 2012). It is the link between computationally generating structures as geometrical objects and their analysis and evaluation that requires permanent improvement. Once this connection is defined by the architects and the structural designers, computational power can be instrumentalised to not only represent but to generate variety and a multitude of possible solution (Bentley, 2002). In several projects (Fig. 1), we worked with structure generating algorithms that create vector-active systems with counter-intuitive placement of elements. The algorithm starts with many versions of systems made from stochastic distribution of structural members. They become the objects of analysis only after the generation and hence do not carry the burden of a preconceived typology.
Fig. 1 A series of projects (Top: Sphere Deutsche Bank, Pedestrain Bridge Reden, Sphere Deutsche Bank. Bottom: Music Pavilion Salzburg, Skyline Frankfurt) investigates novel arrangements of elements within vector-active structures. Based on computationally driven design processes structure emerges from an evolutionary process.
The process of analysis, evaluation, selection and feedback into a subsequent generative iteration becomes the driver of novel approaches beyond well-known systems. The evolutionary principle gradually migrated into the computational design tools of architects and engineers within recent years. The design process of the canopy shows the need for this development. The shortcomings identified during the development of the project pointed towards the need for an advanced tool development that finally lead to Karamba, a plug-in for Robert McNeels & Associates’ Grasshopper.
2 The Canopy
The trade fair company Messe Frankfurt announced in 2008 an architectural competition for the new design of the entrance gates for the exhibition grounds. In the competition the design for two entrances, the north and the south gate, was asked. For each of the entrance gates a canopy with a signalling effect sheltering the service personal and a guardhouse had to be designed. The roof structure consists of crossing flat steel lamellas in an irregular arrangement with a wooden plate on the top. The load bearing girder grid is supported by triangular columns chamfered towards the top. While the southern gate is located on the ground, the northern gate is structurally constrained due to its position on a bridge. The competition-winning proposal designed by Ingo Schrader in close collaboration with Bollinger + Grohmann Ingenieure forms the northern entrance gate for the premises of the trade fair in Frankfurt. The oval shape of the roof - with a size of 20 by 40m - guarantees shelter for rain for the staff at the entrance gate.
To minimize the overall surface of the roof and the overlapping with the public road, which runs parallel to the trade fair entrance lane, the architect Ingo Schrader decided on an oval shape for the roof instead of a circle, which was originally envisaged (Fig. 4). The bottom surface of the roof is the most exposed part since the gate is approached from below via a sloping ramp (Fig. 3). Particular attention was therefore put into the design of ceiling, which became a structural ornament.
Fig. 2 Lamella Configurations for different roof geometries North- South - West Canopy. Whereas the south gate was postponed the north gate canopy with an oval shape and a span of 20 by 40 m supported by 4 columns will be constructed in the summer of 2013.
3 Construction
The roof is positioned on an existing bridge which constrains its column positions. The area that needs to be sheltered, however, defines the roof’s oval perimeter. The two conflicting requirements lead to asymmetric loading conditions with different spans and cantilevers. Therefore, a regular grillage connecting the columns with the roof proved inappropriate and would lead to oversized elements. Furthermore, a hierarchical grid with primary beams between the columns and secondary beams in-between did not suit the architectural design approach. The construction was meant to be minimalistic in its detailing, an approach which is also reflected in the choice of the beam cross-sections.