How to describe the esthetics of structural surfaces? (2/2)

In an earlier post, I wrote about how and why we seem at loss for words when describing the esthetics of a structural surface. I continue that discussion here and analyse what vocabulary layman use and make suggestions for where we might seek additional jargon. I  build my argument upon the results of an experiment carried out by graduate student Rebecca Napolitano in Fall 2016 on the Princeton University Campus.  In the physical experiment, a membrane was installed on a highly frequented location on a central location next to a neo-gothic medium size building.The  membrane was shown in an existing built environment, which might have caused distraction from observing the pure membrane form, but allowed for a full 3D perception of the membrane deforming in the wind.  Randomly selected 138 undergraduate students who passed by the installation, were asked to describe the membrane structure with one word.  If their response coincided with an already recorded word, they were prompted for another defining word.

This physical experiment yielded a plenitude of words which can be catalogued according to formal analysis or subjective response classes. The first category, formal analysis, is grounded in the fine arts and Vitruvian architecture tradition. This type of analysis disassociates itself from reactions such as elation, fear and awe.  These words describe emotions or subjective responses and constitute the second category.  The subcategories in both classes were pre-established before the collection of data and are based on the ones discussed by [1].

Formal Analysis

We first investigated the vocabulary pertaining to the category of formal analysis. This category holds the subcategories of form, proportion, space and visual mass.

Observing the 3D form of the membrane is not a simple process. In the past, built form has been discussed as a hierarchy of simple forms combined according to rules, into an assembly of complex forms [2].  The words in the experiments refer either to the simple or the complex form or the rule.  Simple form descriptions in Rebecca’s experiment included words such as “round”, ”bulbous”.  Complex form descriptions included  “nurbs”, ”free form” and rules included “tangent continuity”, “cambered”, “periodic”, “smooth”, “logarithmic”, “interlacing”, “weaving”, “optimized” , ”linearly disruptive” and “bendy”.

Nurbs, non-uniform rational basis spline (image credit

The subcategory proportion evaluates the geometric relationships between the different parts. Traditionally formal rules for proportioning have been defined buildings composed out of analytical forms including hemispheres and cylinders. Unfortunately, they are not that relevant for force-modeled systems such as the membranes in the experiments, because these membrane geometries are far more complex.  These geometries are generated by the laws of physics and are more difficult to proportion and steer than analytical ones.  A few words like “contrived complexity” hinting at these characteristics, showed up in the experiment.

A number of words in the experiments related to space.  The observers understood space as the Aristotelian idea that the membrane created both a positive space and a negative space or “embrace and grows space”. Words like “encompassing“ (positive space, the membrane itself) and, “limitless” and “unconstrained” (negative space, the space that co-exists separately alongside the space occupied by the membrane itself) exemplified the subcategory space.

Visual mass as opposed to actual mass can be achieved by the perceptions of light, color and texture. The untrained observer tends to make a connection between visual and gravitational mass.  Previous studies show how white surfaces, such as the one in the physical experiment, and the smoothness of the membrane in the experiment helped the structure as being perceived as lightweight [1] . These perceptions were captured in the experiments in the words “sinuous” and “slim”.

Subjective Responses

Besides the words that fall in the category of formal analysis, we closely examined the second category, called subjective responses. The results showed that the observers felt that the membrane has a certain character that spoke to them.  The words were distributed over the subcategories anthropomorphism, sensuality allusion, physical security and empathy.

Some observers saw the membrane as a living creature (eg. “sting ray”, “cocoon”) and endowed it with personality and intent. This association is called anthropomorphism.  The membranes were also perceived as “pregnant in the breeze”, “in bloom” and “about to take flight”.

Many observers found that these surfaces had a sensuous quality and captured those impressions in words like “sensual”, “voluptuous” and “calliphygian”. These words refer to the movement of the membrane as it progresses to a visual climax, followed by a relief of tension. In particular the inward and outward curving membrane surfaces have a particular sensual quality, which is missed by forms with single curvature.

Some spectators covertly or indirectly referred to an object from an external context.  The membranes evoked allusions with words such as “Rubenesque”. This word for example refers to the works of the Baroque painter Pieter-Paul Rubens (1577-1640) and means plump or rounded in an attractive way.  Other images included poetic metaphors such as “symphonic”, “motion frozen in time”, “essence of motion”, “natural choreography”.  Other allusions included scientific, artificial natural associations such as “meniscus”, “satin/silk, “hilly” and “motion of water”. These references to physical objects, although they are not grounded in the innate perception of the observer, contributed to aesthetic experiences while viewing the membrane.

Anthropomorphism, an association to a sting ray (left ), allusions to Ruben’s works (right), ,silk (bottom right) and hilly (bottom left) call the membrane in the wind to mind without mentioning it explicitly. (image courtesy Flickr the Commons)

Physical security is evaluated based on one’s intuitive concepts of structural behavior. Previous studies [1] claim that light structures can evoke feelings of fragility as opposed to the feeling of security evoked by a for example gravity concrete dam. In contrast, observers in the membrane experiments referred to the membrane as being “calming” and “effortless”.

Some observers apply terms like “meandering in the wind” to the membranes because they identify or empathize with them. They imagine how they would feel if they were thin membranes fluttering under dynamic wind loads and use words like “lively”, “playful”, “vibrant” and “audacious”.

Meandering System (image credit

The plethora of words describing the aesthetic response of observers to a membrane covers a wide range of subcategories and depends upon the observer’s previous experiences and education.  It is important to recognize that some of the words in these experiments fitted within the formal analysis categorization. This categorization evaluates form, proportion, space and visual mass. However unlike rectilinear systems, the qualities praised in curved surfaces did not exclusively fall in these categories and included non-Vitruvian terms like “oscillating”, “structure in motion”, “free form” and “fluid”. Besides these formal qualities, these lightweight structures also evoked jargon around emotions and associations.

Few words in the experiment related to the proportion of these slender curved systems.  Unlike theories about classical beauty, few works in literature relate to proportion in 3D curved shells and tents.  The engineer’s attitude towards appropriate proportions in these systems might be biased towards rules that maximize structural efficiency. For example the arch and cable height to span ratio should lie in the range of 1/4 to 1/7 for an arch, and 1/10 for a cable, so that the material is used in an efficient way.  But by enforcing these engineering rules as aesthetic rules, one might forego the opportunity these systems afford to express sentiment, which might demand much more pronounced ratios. The anthropomorphic allusions, found in terms such as “sting ray” and “cocoon”, point towards another potential approach that could enrich the formal analysis of tents and shells with respect to the evaluation of proportion. Proportion (and also scale) rules for these typologies might be established from mathematical algorithms that relate biological forms to mechanical phenomena, such as the rules found in the work of D’Arcy Thompson [2].

The description of form in the experiments lacked in exact definition. The shape of a membrane depends upon the flow of forces within the membrane, and is rather complex in 3D.  Vocabulary such as curvature, anticlastic, synclastic, etc. was distinctly lacking from the words in the experiments.  It was also observed that jargon used in the description of fashion design, was also distinctly lacking (eg. flare, drape, cling, etc.)  These observations might be due to that fact that the observers might not have been trained in those disciplines. However it is suggested that a great wealth of descriptions could be obtained from those fields.

Other observations acquired through the senses of smell, touch and hearing were not found in the experiment words, and by definition were not categorized in the formal analysis, which relies purely on visual perception.  In contrast, the Merriam-Webster definitions of aesthetics includes ‘appreciative of what is pleasurable to the senses’. A formal analysis, deprived of tactile, audio and olfactory experiences, seem only to capture to a certain extent the aesthetic intent of curved surfaces.  For example the concave shells of the Stage by the Sea (Flanagan Lawrence, 2014, Littlehampton, UK), a social performance stage, enhances the acoustic quality of the adjacent green space and hence contributes to its aesthetic appreciation.

Stage by the Sea (Flanagan Lawrence, 2014, Littlehampton, UK)

Despite the limited available jargon to describe the aesthetics of force-modeled structural systems, this discussion has started to establish a critique approach drawing on formal analysis and subjective responses. Lost for words, it is suggested that additional enriching jargon, criteria and perception might be found in philosophy, psychology, visual arts, fashion design, architecture, mathematical biology, and in the senses beyond vision.

From an educational perspective, the experiment allowed the students to start recording and discussing the esthetics of a structural curve surface.  All too often students, especially from engineering or scientific fields, feel reluctant to engage with such a discussion.


[1] A. Holgate, Aesthetics of Built Form, Oxford: Oxford University Press, 1992

[2] D.W. D’Arcy Thomspon, On growth and Form, 1942.

Author: Prof. Adriaenssens


I would like to thank Rebecca Napolitano for designing and setting up the experiment and collecting the data.

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