Shaping better civil structures – Sigrid Adriaenssens, Princeton University (featured article Rumoer 56)

This is the featured article of the upcoming Rumoer 56: Form Finding architecture. Get a glimpse of what you can expect in the full edition by reading this article about the research being done in Princetons Form Finding lab!

Rumoer 56 is expected by the end of this month.

Sigrid Adriaenssens, PhD, is a structural engineer specializing in the form finding of structural surfaces. She is an Assistant Professor at the Department of Civil and Environmental Engineering at Princeton University, USA, where she directs the Form Finding Lab. Adriaenssens holds a PhD in lightweight structures from the University of Bath, UK, and worked as a project engineer for Jane Wernick Associates, London,UK and Ney + Partners, Brussels, Belgium . She is the first author of “Shaping Forces: Laurent Ney” (A+ Editions (CIAUD-ICASD), 2010) and “Shells for Architecture:Form-Finding and Structural Optimization” (Taylor and Francis, 2014).

Prof. Sigrid Adriaenssens, Form Finding Lab, Princeton University, USA,

1.     Introduction: Improving the quality of urban life

By 2050, 70% of the world’s population will live in cities. Fifty percent of the world’s population currently lives in an urban environment and produces more than 75% of all C02 emissions. Finding intelligent and efficient ways to provide more people with fewer resources will make cities more resilient to manmade and natural disasters and reduce their impact on the environment. The long-term research goal of my research group, the Form Finding Lab at Princeton University, USA, is to transform the engineering design framework for a future-oriented built urban environment.

Our research addresses the following core questions:

1. What is the relationship between form and efficiency in civil structures? (Section 2 answers this question); and

2. With increasing emphasis on the preservation of natural resources, how can design theories and tools match untested sculptural ideas to the construction of feasible and material-efficient structures? (Section 3 explains this question.)

2.     Dialectic Form

Contemporary designers of curved structures seem to be guided by only one of the following design drivers: (i) analytical geometry, (ii) sculptural aesthetics, or (iii) structural efficiency. The behavior of shape-resistant structures depends mostly on their global spatial configuration (e.g. shells), and less on the properties of their individual components (as in the case of frames). Analytical geometry is a tool that has been used since antiquity for the generation of architectural shapes. These forms, found in the Pantheon’s spherical dome (Rome, 126 AD) or Felix Candela’s hyperbolic paraboloid shells (Mexico, 1950-1997), are limited by the rules imposed by analytical geometry and the designer’s imagination. With recent geometrical modeling tools, such as Rhino and CATIA, more designers base their free- form ideas on aesthetic considerations to achieve dramatic results. This design approach expresses sculptural intentions, as experienced in Gehry’s Bilbao Guggenheim Museum (Bilbao, 1997) but is disconnected from any intent aimed at structural efficiency. This design methodology needs a good team of engineers and contractors to make the sculptural form stand up, supported on an add-on uneconomic structure. The complex curved surface design challenge lies in determining the ‘right’ structural shape that will resist loads within its surface without the need for extra structural systems.

Our research entertains a dialogue between structural curved form and other non-structural design drivers, an approach we refer to as “dialectic” form-finding. The word “dialectic” stems from Ancient Greek and refers to a method of argument for resolving disagreement. In the context of our research, it stands for the resolution/integration of competing (and sometimes conflicting) design drivers through a rational engineering approach. Typical design drivers for urban infrastructure are cost, technical quality (structural, environmental, and construction efficiency), urban planning (context-sensitivity) and architectural design. Our research focuses on dialectic forms driven by structure and environment, structure and construction, and structure and material. In this paper we concentrate on forms driven by environmental and structural considerations and demonstrate how designers can create structurally efficient forms that use minimal natural resources, and maximize occupant comfort by guiding the flows of sun, wind, and light.

2.1.         Modern Dialectic Building Forms: 

The folded hyperbolic paraboloid (hypar) shells of the Miami Marine Stadium (Miami, 1963), shown in Figure 1a, clearly showcase that structural and environmental issues can be drivers for form-generation instead of being constraints. The form of the folded hypar concrete shells imbues the grandstand roof with structural efficiency.  This efficiency is exemplified by small deflections and stresses (even under hurricane wind loads, typical for the Carribean Region) (see Figure 1b). Additionally the shell roof design attains environmental efficiency and maximizes spectator’s comfort in a warm and tropical climate.  The hypar shapes and their orientation, parallel to the prevalent South-East ocean driven winds, provide effective shading and temperature control as shown in Figure 1c.

2.2.         Site-specific sun shades for the prevention of skin cancer.

Annually, 1.3 million Americans are diagnosed with skin cancer, currently representing more than 50% of all cancers in the USA. Childhood exposure to the sun’s ultraviolet (UV) light increases the risk for skin cancer as an adult substantially. Starting positive sun protection early is therefore key to reducing the incidence of this disease. Natural shade provided by trees does not offer adequate UV protection. Available sun shades are mostly driven by aesthetic appeal and “one design fits all” uniformity and do not necessarily shade the intended area ( see FFigure 2a). The protective ability of a shade depends on its orientation in relation to the seasonal and hourly incidence angle of the sun. This site- and time dependency is ignored in commercially available shades. We are developing and testing the digital design to manufacturing workflow for a novel type of sun shell that efficiently shades and passively cools outdoor areas using location specificity. This grid shell of angled louver beams are environmentally and structurally optimized for each specific geographic location. (Figures 2b,c and d)

3.        Design tools and theories

The construction industry is one of the most resource-intensive sectors. In recent years, research in the field of the design of sustainable structures has mainly focused on quantifying the environmental impact and life cycle cost of existing structures. A life cycle assessment approach quantifies the environmental effect of a design once the design is completed.

Unfortunately, little attention has been paid to developing structural design methodologies and tools that advocate sustainable design through minimal use of materials. Traditional structural design is aimed at well-defined codes that guarantee structural strength and serviceability. These codes, however, set no specific requirements regarding the structure’s environmental impact.  Due to the challenge of building more economically and sustainably, structures should be conceptualized with material and current available fabrication techniques in mind. The advent of digital modeling, optimization, form-finding and manufacturing technologies have given designers a new toolbox.

3.1.    Form-finding of shape-resistant structures:

Form-finding is the process of generating shapes that are in static equilibrium for a pre-defined set of boundary conditions which include internal and external loading, support conditions, element and material properties.  A comparison of two similar-looking lattice roofs, the Beijing National Stadium (Bird’s Nest, Herzog and de Meuron, 2008) and the Royal Soccer Club Anderlecht roof (for Ney and Partners, 2008) – a structure for which we performed the form-finding – reveals steel quantities and associated C02 emissions of 430kg/m2 versus 130kg/m2 and 745kgCO2/m2 versus 225kgC02/m2 respectively (shown in Figure 3).  This comparison clearly shows that form-finding techniques have the potential to generate structurally stable shapes that are financially and environmentally economic.

The development of numerical form-finding algorithms and tools builds on my Ph.D. research that derived beam algorithms for a form-finding technique based on dynamic relaxation. These beam and other newly developed co-planar algorithms made the design and construction of the steel and glass grid shell over the Dutch Maritime Museum possible (Ney and Partners, Amsterdam, 2011), and it has been praised for its slenderness.

In the late 17th century, the historic stone building that now houses the Dutch Maritime Museum, was an instrument and symbol of Dutch maritime power (see Figure 4).  The development of the Dutch seafaring nation was closely linked to the production of sea charts and the associated sciences (particularly geometry, topography and astronomy).  This building, a former warehouse, used geometry as a basis for its design and seemed particularly suitable for a museum in 1970.  At the beginning of the 21st century, the building no longer met the needs of a museum. As a result, a design competition was held to cover the courtyard, as a reception area, with a translucent roof.  The design brief stipulated that the new design should not damage the historic building and that any addition or change to the building’s heritage should be reversible.  Laurent Ney chose the initial two-dimensional geometry for the steel/glass roof in order to tell the visitor a story about the building’s history and its close relationship to the history of the sea. At the origin of this 2D geometry lies a loxidrome map with 16 wind roses, a figure used to mark out the course for ships (see Figure 5). This geometric pattern is found on every sea chart of the 17th century, the time period the museum was built.  This pattern forms the basis for the structural mesh of the proposed steel grid shell (see Figure 6). This mesh references the power of the Dutch fleet and reinstates this former admiral building as a symbolic center of the Dutch mastery of the seas.  The multi-axisymmetric mesh also reinforces the monumental architecture of the 17th century building. Based on this strong contextual mesh, we used form-finding techniques and facet planarity algorithms to stir the form of the steel/glass grid shell shown in Figure 7. This realized structure has been well received and appreciated by its local community, its users and peer professionals and won the 2012 Amsterdam Architectural Prize as well as the 2012 Dutch and Belgian Steel Award.  De Groene Amsterdammer writes about the joy of experiencing the cupola: “Of course, we all envy the museum’s night guard who gazes at the stars through the 1016 pieces of glass that make up the magnificent cupola designed by Laurent Ney. At least when the courtyard is not populated with adults and children, sitting on the floor eating their homemade sandwiches.” (see Figure 8)

Hard infrastructure is intended to last generations. As structural designers it is our professional and civil responsibility to improve the quality of life of the rapidly increasing urban population, to make cities more resilient and to reduce their impact on the natural environment.