Structural design possibilities

The layers of structural function and dimensions are closely related. There-fore symbols only are developed to express one of these two layers in the new structural language, namely structural dimensions. (For each characteristic of structural dimension, one specific characteristic of structural function is attributed.) These symbols can be implemented on different structural elements. These conceptual elements can be represented in one, two or three dimensions.

Each distinct combination of force or moment transfer (within structural dimensions) and element is represented in Figure 7-15. A distinction is made in the orientation of the applied symbol for parallel transfer of force and moment in a two-dimensional element, as this orientation has a different implication for the structural dimensions of the element.

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Figure 7-15. Structural function and dimensions in combination with elements.

For each structural (conceptual) element with specific characteristics of structural dimensions, a range of structural design possibilities can be presented. These design possibilities are to be understood as materialized structures that are already built, or at least designed in detail.

These materialized structures also operate in the realm of architectural design solutions, and thus can be characterized by architectural qualities as well. This layer of structural design possibilities forms a link between structural and architectural design solutions.

Each structural design possibility can be categorized through its specific characteristic of structural dimensions and the conceptual shape of the architectural element. (In this conceptual design collaboration, a structural el-ement originates from an elel-ement of architectural design.) For example, a structural element of a rectangular surface with the structural dimensions characteristic of parallel transfer of force represents a range of design

possibilities: a steel frame with a tension cable, a concrete Vierendeel-girder, a wooden truss-girder and so on (Figure 7-16). Turned around, this means that each of these design possibilities has the architectural conceptual

characteristic of rectangular surface and the structural dimensions characteristics of parallel transfer of force.

7. A structural language for conceptual design

141 Figure 7-16. Structural design possibilities: rectangular surface + parallel transfer

of force.

Other examples are given for a rectangular surface with an axial transfer of force, one under tension and one under compression. For the former combina-tion, this leads to the design possibilities of a plywood panel, steel cables strung between hollow steel sections, and a slender concrete wall with a hole.

For the latter combination, the design possibilities are a thick brick wall, a concave concrete wall with some window openings, and a steel frame of hollow tubular sections.

Structural engineers are familiar with designing structures by using structural typologies (like beams, column, slabs and girders). The structural design possibilities this layer addresses are further developed structural typologies or combinations of typologies. They are the end result of a

structural engineer’s design process: a built or ready-to-be-built structure that performs certain structural functions.

Although engineers are familiar with these structural design possibilities and their link with typologies, the power of this layer lies in the link between conceptual design and the wide range of structural design possibilities (rather than a single design solution). As engineers seem to be only modestly trained in conceptual design and in developing structural variants, attention might be needed to support engineers with this layer during collaboration to keep in mind the wide range of possible design solutions a conceptual design entails.

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Figure 7-17. Structural design possibilities: rectangular surface + axial transfer of force.

For example, in Cecil Balmond’s structurally creative design of some columns for the Kunsthal in Rotterdam (with architect Rem Koolhaas), the engineer investigates the wide variety of design solutions available for a conceptual element that transfers its load axially under compression (i.e. a column). Also, in designing the roof as a wind-bracing element (i.e. a parallel transfer of load), the investigation into possible structural solutions leads to a creative solution: a horizontal arch (Balmond 2002).

In the field of architectural design, it is common to find inspiration for conceptual design in built reality (cf. precedents in Chapter 2.3). By providing possible structural design solutions for conceptual elements in a built reality, structural conceptual elements enter the realm of architectural design, where they can be evaluated as architectural elements through their visual and tactile characteristics.

In the collaboration between architect and structural engineer, this layer provides a link between a structural conceptual design proposition and the wide range of structural design possibilities. Meaning is given to a design proposition through abstract terms that avoid a more limited description through structural typologies derived from a more in-depth understanding of structural analysis. (What’s more, these typologies are often associated with

7. A structural language for conceptual design

143 stereotypical visual and tactile characteristics that also diminish the range of

possible design solutions. For example, a truss-girder is often represented as a stringent rhythm of steel H-profiles, although other configurations are also possible.) This layer enables an architect to understand the richness of possible structural design possibilities for a conceptual proposition.

Developing a catalogue of built structural design possibilities for an architectural project can provide a tool for presenting a wealth of design possibilities as an inspiration for collaborative design work. This catalogue can be organized through the layer of structural dimensions and the conceptu-al (architecturconceptu-al) shape of the structurconceptu-al element. Such a catconceptu-alogue relates to Goldschmidt’s catalogue of ‘precedents’ or ‘references’ as a design

knowledge database, which in this case overlaps architectural and structural design (Goldschmidt 1998).

Going through a range of built examples for inspiration is a known method in architectural design. For the structural engineer, such a catalogue can provide an overview of possible design solutions, which might prevent a structural design process aimed at finding only one solution (cf. Chapter 2.3).

Such a catalogue can also be used as a communication tool during negotia-tions between architects and structural engineers, helping them to express and refine their design characteristics and design intentions to each other – and also to themselves. For example, a built solution can present the kind of expression an architect is seeking in his or her design, or the structural scheme an engineer prefers.

The strength of this layer lies in the structural and architectural variety of possible structural design possibilities that can be provided for each

conceptual combination. A catalogue should provide for this variety and for an appropriate retrieval method to present adequate design possibilities during collaboration.