Parametric Engineering

Everything is Possible

Florian SCHEIBLE Director Knippers Helbig Advanced Engineering Stuttgart, Germany fs@knippershelbig.com Florian Scheible has joined Knippers Helbig in 2003 after receiving his architecture degree from Stuttgart University and working in various architecture and engineering firms. He has been project manager for large scale projects and has given several lectures at international symposia.

Milos DIMCIC PhD student ITKE, Stuttgart University Germany m.dimcic@itke.uni-stuttgart.de Milos Dimcic, born 1982, started his PhD studies at the Stuttgart University in 2009, after receiving his architecture degree from Belgrade University. He worked for Knippers Helbig from 2007-09 on various large scale projects, like EXPO Axis in Shanghai and Shenzhen Airport.

Summary With the 300.000m² three dimensional folded façade, Bao’an International Airport in Shenzhen is one of the largest parametrically defined buildings in the world. This paper is addressing the application of automated, parametric procedures, used to design some of the world largest free form structures. By comparing different projects realized by Knippers Helbig Advanced Engineering, different approaches for achieving a structually and visually optimal design are explained, as well as principal methods of cooperation between architects and engineers.

Keywords: parametric design, icon buildings, integrated design, MyZeil, Bao’an International Airport, Westfield

1. Levels of Intervention

Complex geometries and doubly curved structures have become the standard of iconic building design nowadays. With the rapid advancement of digital technologies over the past few years, the main interest was research oriented towards the development of appropriate software tools and the establishment of modern work flows in order to bring design to production. Meanwhile the software market is concentrating on few tools such as BIM or methods such as parametric design. The phrase parametric design describes a wide range of approaches, currently revolutionising the building industry. Basically it describes a process of transferring intellectual decisions into computerized optimization procedures and it is widening the field of potential designs and technical solutions. But it is also changing the way of understanding planning processes. It is one of the great challenges to make sure that such processes do not become isolated parts of the design process, but to be integrated in every phase and reflect the high complexity of the design process. Free form design offers the chance to investigate new approaches to optimize material

usage and consider sustainability aspects. The label everything is possible bears some risks, but many architects and planners are evaluating the advantages and potential of integrated design solutions. This paper is trying to demonstrate different approaches to bring the complex design to reality. For this purpose, several projects done by Knippers Helbig Advanced Engineering, were chosen and categorized according to the level of intervention needed to obtain a statically optimized and eventually buildable solution. Depending on the point in time when the methods of automated structural design are employed in the process the design can be steered efficiently into different directions and difficulties can be avoided (or have to be solved later). The presented projects range from the ones where structural engineers were involved from the beginning, to the ones where a compromise was found in the middle of the design process, and finally to the project of the Bao’an International Airport where there was limited space to change the design and all problems arising from the complex geometry of the facade and the structure had to be solved by programming. It is demonstrated how the new understanding of architecture, emerging production technologies and parametric design tools have to go hand in hand with the traditional understanding of engineering and detailing.

2. Adapting Form

The Westfield Mall in London is one of the largest shopping centres. Three free form roofs are covering the two mall boulevards and the central plaza. Knippers Helbig was appointed as subcontractor of Seele to develop a solution for the two boulevards.

The architectural idea of Benoy architects was to visualize concentric waves within the free form roof to bind together the three different areas of the mall. In collaboration with the architect and Seele the wave direction was modified in order to utilize the wave height as structural height to span the 25m width without any additional substructure. The waves can be understood in terms of inclined lattice girders leaning against each other. At the crossing points, domes were introduced in order to generate shell effects. They are supported at four opposite points and span up to 35m.

During a complex iteration phase the overall shape was adjusted step by step to serve additionally as smoke barriers by different low points of the valleys and to minimize material consumption and profile height.

Fig. 1: waved roof under construction; Picture: Seele

Fig. 3: MyZeil, Frankfurt; Arch. Fuksas

Another aspect was to minimize the faceting effect due to the small curvature of the waves in order to avoid a strong visual impact as well as ponding in the valleys. Therefore the wave direction and grid layout had to be adjusted. Because the small slope of the roof, the gird was projected to reduced the fabrication complexity.

3. Form and Structural Optimization

3.1 MyZeil, Frankfurt

MyZeil is a shopping mall in the center of Frankfurt, Germany designed by the Italian architect Massimiliano Fuksas. The gap between the main building volumes is covered by a slender steel glass roof structure. The originally kinked shape of the roof required large trusses for support in

order to span about 45m. In order to avoid additional structural elements two horns were transformed into mega columns and such that instead of being suspended from the roof, they are supporting the structure. By smoothing the overall shape bending moments in the steel members were reduced and shell effects were activated. This allowed spanning with steel cross-sections of 65x120mm without any additional support and creating a column free shopping-mall.

The basis of this process was an intense discussion between the architect and engineer via Rhino-files. Once the shape was fixed, the surface had to be changed into a grid. Regular grids such as the roof of the British Museum were excellent examples but did not fit the complex shape of MyZeil.

Fig. 2: Comparison of original (lef) and optimized scheme (right)

Fig. 5: Sun Valley at Expo Boulevard

Standardized tools from Catia or other modelling software did not lead to satisfying results since those meshing tools start from the boundaries and not from the centre. Additionally it became clear that the high number of boundary conditions will require a clear setting. Therefore lines of

orientation were introduced as well as fixed points allocating the grid of the adjacent facade parts.

By using subdivision routines such as those originally used by Buckminster Fuller and subsequently relaxing the grid subjected to geometric constraints such as the edge length of the individual faces, the grid was generated in several stages. [1,2] The steel sections have been optimized within the structural analysis. Wall thickness and sections dimensions are changing according to the structural conditions in order to minimize the material consumption and create a structure as light as possible.

3.2 Expo Boulevard, Shanghai

For the Expo 2010 in Shanghai Knippers Helbig Advanced Engineering designed in collaboration with SBA Architects a lightweight membrane and steel-glass structure to serve as an entrance building. Currently, the building is being converted into a shopping mall at the centre of a new suburban district. The structure is 800m long and 100m wide. The combination of both types of structural systems leads to a unique design. The six sun valleys direct the sun light to the lower levels.

The sun valleys are single layered grid shells with a height of 40m and a diameter from 18m at the bottom to 85m at the top. Due to their extreme cantilever and high local bearing forces introduced by the membrane connections, the development of the shape required several iterations. The result is a compromise between the architect’s interest to achieve a slender shaft and the structural optimum of a direct connection between bottom and edge beam. Once the shape had been finalized

the grid layout was to be determined. It was decided to keep the main lines at the top edge circular in order to deal with the large loop stresses in the most natural and efficient manner. Second, it

Fig. 4: Original shape (left) and final shape (right)

Fig. 6 Grid layout, Picture: Wilfried Dechau

Fig. 7: Bao’an International Airport, Shenzhen; Arch. Fuksas;

Picture M Fuksas Arch

became clear that the main lines at the bottom had to run vertically in order to bear the huge normal forces from compression and tension. To achieve the change in direction and to deal with the different number of triangles at the lower and upper edge, special nodes were introduced. Their location was coordinated with the overall visual impression and the membrane connections which required a denser mesh to take the local bending forces. The design of the rectangular hollow sections was adapted to the local stress conditions. High normal forces lead to thick webs and flanges or even

full sections, high bending moments around the membrane connections required significantly higher section dimensions resulting in about 50 different section types.

4. Fixed Form – Parametrization

The design of airports has become one of the most attractive tasks for architects. Having the function of ‘entry gates’, cities all over the world have understood that this is a great chance to present their intended image. The technological centre of the Southern Chinese industry area Pear River Delta Shenzhen is one of the wealthiest cities in China. Therefore the brief required an outstanding and unique building shape. In analogy to biological shapes Massimiliano Fuksas decided to break up the symmetry and many conventions of traditional airport buildings and to go for a free form shape with more then 60.000 different facade elements. The same number of different glass panes is carried by a light steel structure of around 400.000 individual structural members.

The strong formal approach made an optimisation of the overall shape almost impossible. Some minor adjustments of the form helped to reduce the total steel weight slightly. Another important design aspect was the bearing system in order to reduce and distribute local earthquake loads to create a joint free structure and facade. The main focus was on the geometrical development of the steel structure and the façade. The generation of the façade and roof

elements of the Shenzhen Bao’an International Airport, has been automated with bespoke in-house software tools. This enabled to generate a double truss structure over a given free form surface, including aspects of sustainability, day light control, energy gain and architectural design intends were influencing the final design which required several adjustments of façade layout. The manual drawing of structure and facade would take an unacceptable amount of time especially once it comes to changes. The only possible way to deal with this kind of task is to parametrically define the entire structure so that with each change of the form all elements can be generated within hours, or even minutes.

The 300.000m2 of free form surface was divided into a huge point cloud. This system of points was arranged in four layers. Two inner layers served as the basis for a double-layered grid structure and two outer layers for the generation of facade elements. The free form surface was unrolled so that the facade elements can be represented in an Excel spread sheet, and since there were 20 different types of facade panels (with different angles and openings), architects were able to simply fill the spread sheet with different colours and numbers, representing different elements (Figure 8). The software written for this purpose was able to extract that information from an Excel file, generate appropriate facade elements on the

desired spot and fix all problems that arose in the process. Fixing problems refers to the adjustment of the connections between different elements and automated geometry perturbations performed in order to always keep the glass part of the facade planar - which was one of the main conditions and one of the biggest challenges, considering the double curvature of the surface and the complexity of the elements. Combining different software, like in this case, enables an efficient cooperation between designers and engineers. There is one core software, programmed to automatically generate the structure and facade and there are many input branches that allow the definition of new elements, new structural pattern, the entire facade element disposition (like the Excel sheet shown in Figure 8), etc. This provides the flexibility to experiment with different settings, because after each change of the element, the definition of a new element type or structural system, the entire system can be generated automatically within a very short time. Today parametric design programs are conquering the market, but are often used for some basic design development. In this case, heavy steel and aluminium parts without any space for errors in the geometry had to be produced. That is why original methods had to be developed in order to deal with specific problems of this project.

Fig. 8: Parametrical definition of the facade

Fig. 9: Bao’an International Airport, Shenzhen

The fixed shape approach is a design driven method where structural efficiency and production abilities come second. The main advantage is the enormous freedom in sculptural expressiveness of the architect. The disadvantages are the bigger programming efforts required to generate a statically efficient structure and automatically fix all the geometrical difficulties that could cause problems with fabrication of elements. There is basically always a

trade-off between the freedom of the architect in shaping the form and the effort needed to program methods that will automate the generation and production of structural and facade elements.

5. Conclusion

The aim is to utilize the evolving computer oriented approach in order to achieve better, more integrated solutions. The new technologies are not replacing but complementing and enriching the traditional ways of cooperation between architects and engineers.

Aspects like design, cost and material efficiency, sustainability, production and assembly strategies influence the decision process. Therefore the higher the level of cooperation from the beginning of the project is, the easier the process from design to production. Today, for projects with complex geometry like the ones presented here, programming and code development are an important part of architectural design and engineering. The level and the way of cooperation between designers and engineers is slightly changing, creating a new area of expertise between those two fields – an area occupied by experts with the knowledge in design, programming and static analysis, that can solve the problems of structural design and fabrication arising from the complex geometry of the free form architectural design.

List of Projects

MyZeil, Frankfurt Germany

Client: MAB Projektentwicklung

Architect: M. Fuksas Frankfurt, Rom

Expo Boulevard, Shanghai

Client: Shanghai World EXPO Land Holding Co. Ltd., Shanghai

Architect: SBA GmbH Shanghai/Stuttgart

Cooperation: ECADI, Shanghai

Westfield, London

Architect: Buchan Group International, Benoy

Cooperation: Seele GmbH & Co. KG

Bao’an International Airport

Client: Shenzhen Airport Group Co., Ltd

Architect: M. Fuksas, Rom

References

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[2] Linkwitz, K. and Schek, H.-J., Einige Bemerkungen zur Berechnung vonvorgespannten Seilnetzkonstruktionen’, Ingenieur-Archiv 40, 145-158, 1971

[3] KNIPPERS J., HELBIG T., SCHEIBLE F., Sun Valleys and Membrane – Structure and Construction, DETAIL 11/2010

[4] KNIPPERS J., HELBIG T., Vom Entwurf bis zur Ausführung frei geformter Netzschalen – eine Prozesskette, Stahlbau Spezial konstruktiver Glasbau 03/2008