It has been said that the work of Frei Otto (Germany, 1912-2015) has a sculptural quality to it . Although Frei Otto’s parents were sculptors, he insisted that the shapes he produced were rigidly grounded in the laws of physics , and was very reluctant to describe their aesthetic value. This observation hints at the questions that this paper starts to address, namely how can one describe the aesthetics of a curved structural surface?
It is observed that structural aesthetic critique is a little practiced discipline. In engineering education, students generally are not encouraged to express their emotions about the built environment, and are not frequently encouraged to develop an enthusiasm for visual experiences . Beauty seems to engineers such a vague concept, hard to define accurately to others.
Structural engineers feel most secure critiquing when they voice their opinion about the appropriateness of typology and form when the structural system has withstood the test of time. For example, the designs of Vladimir Sukhov (Russia, 1853-1939), are now largely appraised because of their innovative structural resolution of forces in hyperbolic paraboloid and hanging lattice systems 
A few prominent structural engineering critiques , , ,  have voiced their opinion about the aesthetics of structures using criteria besides the choice of structural form. Mostly they have resorted to an approach grounded on principles of ‘formal analysis’. In this approach, commonly adopted in the discussion of aesthetics in art and architecture, the spectator evaluates size and scale, proportion, visual weight, light, color and pattern to establish the degree of balance, unity and harmony. In the critique of bridges and their elegance , , , these parameters have been mostly evaluated according to a ‘classical’ perspective. There are a few key challenges with adopting this classical approach to assess the aesthetic values of curved surfaces. Classicism  praises symmetry, proportion, geometry and the regularity of forms such the hemisphere and the cylinder, not complex geometries like those found in tents and shells.
There is an additional challenge with formal analysis as an aesthetic evaluation approach: this approach can only be appreciated by observers trained with that skill set, and excludes the general public. Responses to curved surfaces also vary with the observer’s personality and experiences. For example, an engineer trained in statics might see aesthetic value in the resolution of forces in a ridge-valley mast supported membrane structure, whereas the layperson might be attracted by the undulations of the membrane surface, reminding her of the desert sand dunes.
In contrast to ‘formal’ analysis, responses to shells and membranes may also evoke emotions such as fragility and joy. In particular, for lightweight structures, observers may feel elated by the perceived victory over gravity. Spectators might identify themselves with those systems and describe how a membrane roof ‘floats’ above the ground. Subconscious allusions might also enhance the observer’s enjoyment. For example, pneumatic membrane structures could be perceived as being womb-like . Such jargon does not necessarily refer to one single clearly defined idea that is universally understood, but nevertheless resonates with individuals.
Based on the arguments listed above, it seems that structural aesthetic critique on structural surfaces is not a well-established discipline. With its main focus on classical formal analysis, it is not well suited for the aesthetical evaluation of complex curved systems such as tents and shells. Nevertheless, it is worth establishing a disciplinary vocabulary to discuss their aesthetic quality, since their aesthetic can enhance the quality of people’s life and hence productivity .
In our next blog on esthetics and structural surfaces, we discuss the results of a number experiments carried out on our Campus that explored the vocabulary used by laypeople to describe the aesthetic quality of structural surfaces.
 L. Glaeser, The work of Frei Otto, New York City: New York Museum of Modern Art, 1972.
 A. Holgate, Aesthetics of Built Form, Oxford: Oxford University Press, 1992.
 E. C. English, “Vladimir Sukhov and the Invention of Hyperboloid Structures,” in Metropolis & Beyond: Proceedings if the 2005 Structures Congress and the 2005 Forensic Engineering Symposium, 2005.
 D. Billington, The tower and the bridge, NYC: NY: Basic Book Publishers, 1983.
 C. Menn, “Aesthetics in Bridge Design,” Bulletin of the International Association for Shell and Spatial Structures, vol. 26, no. 2, pp. 53-62, 1985.
 B. Addis, “Structural criticism and the aesthetics of structures,” IABSE Congress Report, vol. 15, 1996.
 A. Holgate, The Art in Structural Design: an introduction and sourcebook, Oxford: Oxford University Press, 1986.
 F. Leonhardt, Bridges, 1984.
 J. Summerson, The classical language of Architecture, MIT Press, 1963.  A. Holgate, “Lightweight Structures and the Appreciation of Architecture,” First International Conference on Light Weight Structures in Architecture, Kensington, 1986.
Author: Prof. S. Adriaenssens