DREAM BIG: Engineering our world

In the next decade, the USA will have to add 250 000 civil engineers to its workforce in addition to replacing those who will retire. However, only 12.2% of the current USA civil engineers are female. These statistics indicate the need to encourage young people, especially from underrepresented groups in civil engineering, to pursue engineering opportunities in their education. I am delighted to see the efforts of the American Society of Civil Engineers to inspire enthusiastic young innovative minds to enter into the profession with their project DREAM BIG.  This movie is narrated by the Academy Award Winning actor Jeff Bridges. In particular I was super excited to see a large number of our female undergrad CEE Princeton students feature in the Dream Big video Water Wishes for those in need (required watching and enjoy :-)).

dream ig.jpg

Author: Sigrid Adriaenssens

Reflecting on the Future of Design at the IABSE conference

On Saturday, April 29, the IABSE Future of Design 2017 conference was held in New York City. The Form Finding Lab was well represented, with Victor Charpentier in the organization, Professor Adriaenssens as a speaker and alumnus Professor Ted Segal (Hofstra University) leading a design workshop. Demi Fang ’17 summarized the main ideas of the speakers and panelists:

The Future of Design NYC conference kicked off with a vibrant set of “10 + 10 Talks,” in which structural engineers paired up with professionals in a field slightly different from their own. Each pair gave a joint presentation on their thoughts on the “future of design.”

Throughout the five presentations and the Q&A that followed, several recurring themes unfolded.

Technology can be leveraged as a tool to enhance, rather than compete with, the creative human process of design.

Glenn Bell (SGH) and Antonio Rodriguez (LERA) began with a presentation titled “Disruptive Influences as Opportunities, Not Threats.” Rodriguez gave a personal anecdote of a mentor who once warned him against entering the engineering field with the argument that computers would soon take over engineers’ work. Rodriguez explained how he has found that some engineering decisions do, and always will, require human judgment. That’s not to say that technology should be considered a competitor; rather, technology can play a key role in enhancing those creative processes that are best executed by humans.

Antonio Rodriguez of LERA on distinguishing the roles of technology and humans in the future of design.

Bell quoted Chris Wise of Expedition Engineering from a talk at the 2015 IStructE conference in Singapore: “Which bits of the engineer’s life are really human and which should we let go to machines?” Many presenters touched on the importance of this distinction, especially with the rise of digital drawing tools that easily allow for technology to “take over” the design process. Rodriguez made the distinction by identifying the processes at which computers do best, such as repetitive tasks and optimum searches. The use of these technologies “free designers to do what they do best: solving human problems.” He went on to conclude that the “future of design depends on how technology is used to enhance people’s skills, facilitate collaboration, and improve relationships.”

This approach was whole-heartedly echoed in the following presentations. Eric Long (SOM) cited Frei Otto’s scientific explorations of soap film as an example of how “technology inspires design.” As a firsthand example, he cited SOM’s partnership with Altair in topology optimization; fittingly, his presentation partner was Luca Frattari of Altair, who emphasized the fundamental role of these technologies as tools, or “a complicated pencil.” Sigrid Adriaenssens (Princeton University) presented some of her engineering projects such as Dutch Maritime Museum courtyard roof and the Verviers Passerelle from her practicing days in the Belgian structural engineering firm Ney and Partners. With a nod to David Billington’s principles on structural art, she used these examples to note how “using optimization tools efficiently can allow for efficient, economic, and elegant systems.” Her presentation partner, Bill Washabaugh (Hypersonic), also shared stunning sculptures that utilized engineering technology to not overshadow but recreate motions of nature, such as the rippling reflection of a tree over water, the murmuring of a sea anemone, or the flight of a flock of birds.

With increased levels of collaboration in the design process, broadness and diversity in education can help prepare engineers well for future challenges.

Bell pointed out that the drive towards resource efficiency and sustainability has led to the necessity of interdisciplinary collaboration in the design process. He described his perception of the structural engineer as a T-section, with the “flange representing a broadness in education, and the stem representing a fundamental expertise in structures.” As one of the few educators presenting, Adriaenssens answered one of the last questions squeezed into the end of the Q&A session: what educational approaches should be taken to prepare the next generation for the future challenges of design, which differ greatly to the challenges of the older generation? Adriaenssens shared her conviction in bringing students with different backgrounds into the field of engineering in order to supply a diverse workforce to face these interdisciplinary challenges. “Many of the students I advise are excellent in other fields – they are superb athletes, musicians, or dancers. Asking an 18-year-old to focus on one particular field limits their potential.” She mentions courses at Princeton that bridge engineering with other fields such as the arts, explaining that “aside from the traditional engineering courses, we also need courses that focus on interdisciplinary training,” supporting Bell’s previous statements.

Bill Washabaugh (left) and Sigrid Adriaenssens present their projects that utilize technology as an advanced tool for imitating and perpetuating the systems and aesthetics of nature.

Guy Nordenson (Princeton University) reinforced his colleague’s comments with statements on a more specific type of diversity: “I think Sigrid is a manifestation of where we’ve come and where we’re going,” not just with her more creative and innovative approach to engineering, but also her presence as a female in the field. “Looking out at the audience, it’s great to see that there are a lot more women in the field than when Glenn and I were students. We can do a lot to improve diversity in education starting as early as high school.” Continue reading “Reflecting on the Future of Design at the IABSE conference”

HIGROW – Hygroscopic proprieties of wood used as programmable matter in lightweight construction

Luigi Olivieri, who is visiting the Form Finding Lab this week from the University of Tre (Rome, Italy) with Professor Stefano Gabriele, presents his master’s thesis work:

The project explores the possibilities of using the hygroscopic proprieties of wood as a programmable material. The aim of the research is to explore the possibilities of a temporary structure through a new method of design by studying a shell through the physical behavior of its construction material: wood. The design process is driven by a set of physical tests on the material to come up with an idea for a new pavilion.

View of the exterior space of MAXXI, High humidity – open condition, Rome. [Copyright Luigi Olivieri]
View of the exterior space of MAXXI, Low humidity – close condition, Rome. [Copyright Luigi Olivieri]
The process is divided in two parts, a local and global one. The local part concerns the fabrication process of the structure assembling the local parts taking in consideration the proprieties of wood. The second -global- part concerns the morphology of the pavilion according to the constructive biomimetic principles of a seashell.

Diagram of the design space. [Copyright Luigi Olivieri]
Biomimetic implies the consciousness of understanding natural structures and their process through principles that can be adapted to procedure and technology in the design process. The genome of the project is given by a code that can be adapted to different contexts and through parameters that can acquire multiple variations.

From the study of the seashell, four main principles arise that bring stiffness to the overall shape. The form of seashells is curved in two directions, stiffening the body and distributing the weight efficiently. The distortion of the line in the shell furthermore modifies the distribution of the forces, preventing the shell from breaking.

Experimenting with paper models gives the possibilities to observe how the crease activated by a kinematic movement augments the resistance of a simple sheet of paper.  Transferring the physical system of folding paper into a digital environment, the range expands drastically by using a code that simulates the act of folding.

Study model of paper folding experiment. [Copyright Luigi Olivieri]
By changing the shape of the folding, the result is different every time which allows to create a catalog. The result of this catalog also brings to light the possibilities of using these modules as a self-supporting structure and the ability to develop the surface in a planar sheet.

Diagram for fabrication of modules with positive and negative Gaussian curvature. [Copyright Luigi Olivieri]

The system is already self-supporting, but by adding additional force and bending in the modules, the stiffness increases exponentially. Using the biomimetic principle, behavior similar to that of a pine cone is observed: due to humidity changes an automatic mechanism is triggered generating movement.

The fabrication of the morphological system demonstrates that such a system prototype is feasible. Simple tests inside a humidified control room show that it is indeed possible to measure the curvature of different samples at different percentages of humidity.

The developed fabrication process uses a simple mechanism of absorption and resistance of forces thanks to a special bilayer of plywood. The lamination process takes into consideration how the fibers are layered in the pinecone petal to activate the kinematic mechanism due to the variation of humidity. The evolution of the test reveals that it is possible to control and reverse this mechanism. A joint is also developed in order to merge the components, to allow flexibility of the structure and to simplify the assembly process.

The functional prototype successfully demonstrated that the kinematic structure is capable of rearranging its microscopic cell organization by adapting its shape to various climatic conditions.

Paper model of the global geometry. [Copyright Luigi Olivieri]
Functional prototype of assembled modules in humidified control room. [Copyright Luigi Olivieri]
The output of the project is divided in three levels. First, the hygroscopic mechanism of wood cells and how it can be programmed to achieve different results. Second, the joint that allows the modules to connect together and guarantee mechanical strength. Third, the morphology and the architectural function of the shape.

Micro, Meso and Macro structure hierarchy of the system. [Copyright Luigi Olivieri]

Author: Luigi Olivier. Edited by Tim Michiels.

[thesis work advised by Stefano Gabriele, Luciano Teresi and Stefano Converso]

Luigi Olivieri is an architect and computational designer. He attended “La Sapienza” University in Rome, Italy where he received his bachelor degree in Architecture and Science of the City. During the course of his Master program at the University of “Roma Tre”, Luigi spent his second year at the University of Stuttgart working at the ITECH Master program for the duration of the entire year. He completed his Master’s in Rome with a presentation on material programming as his final thesis. Luigi moved on to work in different international firms from Tomas Saraceno to Fuksas Architecture and Rimond, participating in projects of different scale.

Luigi is currently interested in emergent technology, computational design, and architectural fabrication. He believes that studying emergent structure and natural principles can help architects find a better way of using technology and material to program efficient structures for the future of tomorrow.

What is the value of critique in structural design?

Practicing chefs in the kitchen can revise and refine a recipe to their own satisfaction, yet their progress need not be limited by their own opinion. What might result from allowing a fellow chef or a mentor to taste their recipe? Each taster might give his/her own personal feedback – too salty, not crisp enough – and the aspiring chef, filtering through the responses, may modify and further improve the recipe to a level otherwise unattainable without outside feedback. We find this occurrence in countless other fields; why else might athletes have coaches, and musicians have private instructors? One may be able to accomplish much through individual work, but a trained eye (or ear) observing from the outside can potentially coax an even better performance out of an individual.

Image credit: arch20

It is no different in design. Some design principles that we espouse to our students (such as constraints as drivers of design, drawing as a means of clarifying thoughts, the usefulness of studying precedents, and the iterative nature of the design process) primarily concern the designer as an individual. However, like the chef or the athlete or the musician, designers can only improve on their own to a certain degree. No matter how experienced the designer, outside feedback can add another dimension of considerations that enhance the design.

In structural design, the feedback of a more experienced engineer can be especially important in verifying the suitability and feasibility of the structure. However, that’s not to say that critique from a less experienced engineer is not useful; anyone who has not labored over the design process already has the advantage of seeing the design with fresh eyes and may perceive problems or solutions with greater ease. The act of critiquing is also a valuable exercise for the aspiring engineer, revealing the opportunity to jump into another’s design process and explore the different design decisions that were or were not made.

We emphasize that critique is an opportunity to improve a design; rather than shy away from a critique that may bash on the flaws in a design, designers would benefit from embracing the critique as a way of learning and improving from both peers and mentors.

The Happy Pontist blog discusses in detail the challenges of critiquing works of structural engineering and how to circumvent them. Read more about them here.

The secret of egg tapping boiled down: outsmart your peers on Greek Easter

Once a year, engineers can put shell theory into practice in a less conventional way: by winning their family’s egg cracking competition (also known as egg knocking or egg tapping). On Easter Sunday, it is a tradition for Greek and Armenian families to gather and play a game of egg tapping. Similar traditions exist in many different places such as in Cajun communities in Louisiana or for other occasions, like the Persian New Year Nowruz (celebrated at the beginning of spring).

“As geometric stiffness is inversely proportional to the radius of curvature, the curvier the egg, the better it will perform.”

Here’s how the game works: everyone picks one hard-boiled egg from a basket, and the battle begins. In a knock-out tournament, several players hit their eggs against each other, first bottom-to-bottom, then when bottoms are broken – top to top. When a player’s egg is cracked on both sides, he or she is eliminated. The game continues until one player remains with an intact side of their egg, and he or she is proclaimed the winner.

Egg tapping, red won [By Superbass – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=3767798%5D
Several approaches on how to outsmart your opponents in this game exist. Certain crafty rascals suggest manufacturing eggs from cement mortar or wood. Others resort to the less labor-intensive freezing of eggs. These cheats, however, will likely get you caught and we recommend you steer clear of them. Other strategists advise without any rationale, picking the largest egg or eggs from free range hens as their shells are allegedly thicker. We doubt the scientific basis for any of these suggestions and recommend you instead follow the guide below.

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Local egg shell failure due to impact load.

But first some structural mechanics. The mechanical behavior of shells is predominantly determined by the overall shell shape. When observing the failure mechanism of the egg shells, you will see a relatively small depression with some cracks (as shown on egg B above). This failure mode in shells is called local buckling, and is caused by the sudden excessive deformation of the super thin shell due to the impact of the other shell. But why did shell B break, rather than the egg used to break it?

How much a shell deflects can be predicted through what engineers call the shell’s stiffness. Stiffness depends on two factors: material properties (material stiffness) and geometry (geometric stiffness). For egg shells, geometric stiffness dominates the behavior, especially as the material of all eggs is basically identical. Thus, the secret of winning the egg challenge can be boiled down to the (local) shape of the egg. As geometric stiffness is inversely proportional to the radius of curvature, the curvier the egg, the better it will perform: geometric stiffness   ̴   1/radius.

Eggs capture
Top of the left egg shell has significantly lower radius of curvature than top of the right egg shell and so the left egg will be much stiffer (2D-simplification).


That gets us to strategy:

Step 1:  Pick the pointiest egg in the basket. The importance of this step cannot be stressed enough. Only the top part of the egg matters. Size and thickness are of very little importance. Curvature is key, but make sure the egg has no pre-existing cracks (like egg D). For example,  if  you were to consider the eggs pictured below, egg C would be the best choice.

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Egg C has the most curved top. It’s bottom is also less flat than for example B’s bottom. Egg D is almost as curved as C at the top (although this is less visible in the 2 D picture), but has very small cracks that have been highlighted in black.

Step 2: Polish your egg. The buckling phenomenon described above is dominated by curvature. However, local buckling can be facilitated though small imperfections (like small bumps) on your egg. Try to remove as many as possible. Also, it it is nicer to win with a clean, shiny egg.

Step 3: Start hitting. Typically, you will first use the bottom of your egg, this part of the game is relatively unimportant. Consider playing strategically: try to steer the game so you can make the first hit when you get to attack the top of the egg of your opponent (see step 4).

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Egg B breaks by hitting it with the most curvy part of egg C

Step 4: all bottoms of the eggs are broken, time to step up your game and get cracking with your pointy top. Make sure you hold your egg in a grip so that it can only be hit at the curviest spot on the top. Buttress the sides with the palm of your hand for extra support.

However, imagine someone picked egg C before you, and you ended up with the less desirable egg D. If you plotted well and are the hitter, you can still win: aim for the flatter area on egg C next to the top (see red arrow below). It does not matter how hard you hit the egg (remember Newton’s 3rd law of action-reaction), the location is much more important.

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Egg C can still be broken by hitting it on a flatter section.

Good luck in your next egg face-off.

Author: Tim Michiels

P.S.: The secret to a delicious egg salad is a splash of vinegar!

You are invited to celebrate our 1st anniversary with us!

We are delighted to be celebrating the first anniversary of the Form Finding Lab blog with you. You have been an amazing audience and we would like to thank you by sharing our highlights with you.

ENGINEERING AND ARTS: We pride ourselves at exploring the intersection of engineering and the arts. We believe that this is important for three reasons. First of all engineering works that elicit an emotional response from the public through elegance of design, increase people’s quality of life and their productivity. No better example than “The refreshing tandem: the works of the engineer Laurent Ney perceived by the visual artist Toshio Shibata”.

Esch-sur-Alzette Footbrodge, LUX(C) Toshio Shibata for Laurent Ney, Design (c) Laurent Ney

Second, innovations that will solve 21st century societal challenges, need to be firmly based on engineering principles, but also must be seamlessly interwoven with art and design. Our rammed earth wall spiral embodied the use of engineered earthen construction combined with an esthetic design intent. The engineering and design were intended to engage and enthuse the local community about zero-carbon structures.

Rammed earth spiral seating sculpture, designed and built in 2016 by the Form Finding Lab

And finally in our work we draw on approaches in art and craft to develop transformative structural designs. The physical and numerical exploration of the Costa Surface, a not well-known minimal surface, allowed us to walk that fine line between material-efficient structure and sculpture.

Numerical form finding of the Costa Surfcea, prior to its contruction

STRUCTURAL DESIGN: Infrastructure is designed to last between 100 and 200 years. Therefore, their long lifespan makes the aesthetic quality of structures also important to society. Some might doubt that aesthetic quality in structures actually exists, but its existence is proven by the number of visitors to the Brooklyn Bridge (New York City, USA, 1883) and the Eiffel Tower (Paris, France, 1887). For several iconic structures, we have interviewed their world renowned designers about how structures achieve a good degree of fit in terms of social, political and historical context, their program, technical quality, cost and context‐sensitivity. We are very proud to have a collection of exclusive interviews with many of the world leading structural, architectural and product designers including Bill Baker, Maria Blaisse, Thorsten Helbig, Marc Mimram, Mister Mourao, Eric Hines, Knut Stockhusen, Doris Kim Sung and Jane Wernick. Through these interviews we hope that our readers recognize good design and hopefully become an advocate for it.

Our visionary cohort of interviewees: Bill, Maria, Thorsten, Marc, Mourao, Eric, Knut, Doris and Jane.

FORMS and ALGORITHMS: Our research blog contributions have discussed form‐finding algorithms and design methodologies that enable unique large span bridge and building forms for a resilient and sustainable built environment. These forms are dictated by the flow of forces. Therefore, the forms can be very thin, cost‐effective, and have low carbon footprint while maintaining strength, stability, and be aesthetically pleasing and comfortable for users. You might have liked reading A structural designer’s new toolbox, Form Finding Flashback: Basento Bridge and Assessing the stability of masonry structures.

side by side
The form found shape of the Basento bridge has been compared to a nun’s headdress.

But most of all we are very grateful for you, our more than 10 000 readers who have come from all over the world to spend time with us on subjects that really matter to us. We look forward to the continuing this conversation in 2017.

The Form Finding Lab Team

PS:  and don’t forget to watch and like our videos on Our Idea Worth Spreading (Tedx talk, Prof. A.), our rammed earth installation Spiraling Dirt,  and Bamboo Structures (Senior Theses Project Lu Lu and Russell Archer) and stay updated by liking our Facebook Page.

Assessing the Stability of Masonry Structures (part 2): Numerical and Physical Modeling

This post is second in a series covering different assessment methods for stability of masonry structures. Part 1 covered classical and equilibrium methods; this post covers suitable numerical modeling techniques as well as different examples of physical modeling for masonry stability.

4. Numerical modeling

Several methods of numerical modeling for masonry structures exist, as demonstrated by the flowchart in Fig. 10.

Figure 10: Overview of numerical modeling methods for masonry structures, adapted from [41] with [8]
As the first level of Fig. 10 suggests, numerical modeling of masonry structures can be divided into four main categories: macro-modeling, homogenized modeling, simplified micro-modeling, and detailed micro-modeling. Asteris et al. [41] provide discussions, summarized below with some additions where noted, on the differences between these modeling approaches. Fig. 11 also depicts the different numerical modeling approaches. In this section, macro-modeling and simplified micro-modeling are the focus.

Figure 11: Illustration of different strategies for modeling true masonry sample (a): (b) one-phase macro-modeling, (c) two-phase micro-modeling, and (d) three-phase micro-modeling [41]

4.1 Macro-modeling: masonry as a one-phase material

The macro-modeling approach models both bricks and mortar (or all bricks, in the case of dry masonry) as a homogeneous continuum as in Fig. 11(b). As the subsets under macro-modeling in Fig. 10 suggest, these numerical models are typically finite element models.

Continue reading “Assessing the Stability of Masonry Structures (part 2): Numerical and Physical Modeling”

Belgian Shell Art and Architecture : Marcel Broodthaers and Andre Paduart

This post reflects some of the storyline that Prof. Adriaenssens, invited by the Broodthaers Society of America, will be telling on Tuesday, March 28, 6:30–8pm at Hauser & Wirth Bookshop and Roth Bar, 548 West 22nd Street, New York, NY 10011.


The efficiency of shells is often exemplified by examples of nature. In particular the avarian egg shell and the sea shell come to mind.  A large chicken egg for example is about 4.5cm and has a typical shell thickness of 0.05mm ( slenderness ratio of 900) and could theoretically sustain a load of 14kN (that is the weight of about 14 American football players). The shell can be very slender and sustain high distributed loads because its form follows the flow of internal loading.  To further stiffen against impact loading, some shells in nature are equipped with corrugations like many tropical sea shells.

walking on eggs
Egg shells are amazingly strong under uniformly distributed loading.

Civil shell structures mostly originated in Germany in the beginning of the 21st century, spurred by development of analytical “shell” theory and reinforced concrete. Their evolution in that century can be marked by 3 phases.  These phases also happen to span the biological life of Belgian artist Marcel Broodthaers (1924-1976) who is , among other projects, known for his assemblies of shells of eggs and mussels.

In this post, I briefly describe the history of civil shell design and construction in Belgium in the 20th century and in particular I focus on the work of the civil engineer Andre Paduart (1914-1985), who operated in the same time and geographical space as Marcel Broodthaers.

armoire blanche
White Cabinet and White Table, Marcel Broodthaers, 1965

The early shell period 1912-1940:  utilitarian cylindrical shells in the Port of Antwerp

The initial shell designs were entirely envisaged, analyzed and built by engineers, interested in spanning large spaces without intermediate supports in the most material efficient manner.  The German contractor firm Dyckerhoff and Widmann AG first developed analytical theories to analyze shapes, related to domes (spheres) and vaults (cylinders).  Utilitarian spaces such as warehouses and aircraft hangars were roofed with these shells.  A fine example of such shells can still be found on Kaai 105, 107 and 109 at the Albert Dock in Antwerp, a port city in the North of Belgium.  The fast port reconstruction after the destruction of the Second World War demanded warehouse structures and construction techniques that were cost-effective.  The Belgian structural engineer Andre Paduart designed and built  465m of such warehouse sheds along the Docks in Antwerp. Each shed has 31 bays, covered with a reinforced concrete 8 to 12cm thin cylindrical shell. The shell had a transverse span of 15m and a rise of 3m.  To allow daylight to flood the shed, a rectangular opening (40m x 3m) ran along the crown of the cylindrical shell in the longitudinal direction. To economize, the formwork was re-used each week to build another bay.  These shells still exist today and are structurally significant because they have no edge beams and no permanent tie rods to resist the transverse shell trust.

A few international other significant shells of that period include MarketHall Leipzig (Germany, 1927 – 1930, Dyckerhoff and Widmann AG), Orly Hangar (,France, 1921, Eugene Freyssinet)

Cylindrical Shells in the Port of Anwerp designed by Andre Paduart


Second Period 50’s and 60’s: Iconic shells realized for their visual expressiveness at Expo ’58, Brussels

The increasing body of knowledge in shell theory and construction, initially led the formal language for shells. Internationally, the richness of shells from that era have widely been showcased by the ribbed spherical and cylindrical shell forms of Pier Luigi Nervi (1891-1979) and the hyperbolic paraboloid (hypar for short) thin shells of Felix Candela (1920-1997).  In 1958 Candela built his masterpiece Los Manantiales, a radially arranged assembly of expressive hypars.  In the same year the capital of Belgium, Brussels, held Expo ’58, the first major World’s Fair after World War II.  Iconic pavilions and installations, built for this grand event, included the Atomium and the Philips Pavilion, an arrangement of nine hypars designed by Le Corbusier. Lesser known are the other shells that populated the Expo’58 site including the hypar information kiosk (designed by J.P. Blondel, the vaulted United Nations Pavilion and the semi-spherical Tuilier restaurant.

In 1957,  Broodthaers was a manual laborer on the construction site of the Expo 58 “Avec l’intention de [se] rapprocher des hommes qui la construisent ” [“to get closer to the people that are physically making the Expo”]. In 1958, he published “Another World,” an essay on The Atomium published in Le Patriote illustré, vol. 74, No. 10, Brussels, 9 March 1958, p. 389.

Top Row: Atomium, Philips Pavilion, Information Kiosk, Bottom Row: United Nations Pavilion and Tuilier Restaurant
Marcel Broodthaers as a construction worker on Expo ’58 site, 1957
Marcel Broodthaers, “Another World”, an essay on the Atomium, 1958

Our attention goes out to a more sculptural shell “the Arrow” which dominated the Expo ’58 site. Andre Paduart received from the Belgian government a commission to design and construct a symbol exemplifying the “victory of civil engineering over nature”. The Arrow, a thin reinforced concrete thin folded plate cantilevered 80m and was balanced by a thin 29m span shell on three supports. The folded plate had a tickness of only 4 cm at its tip and the shell on three supports had a thickness of only 6cm.  The cantilever supported a pedestrian bridge that overlooked a scale map of Belgium.  This map showed civil engineering works!  For this incredible engineering tour de force, Andre Paduart and the architect of the project received the 1962 Construction Practice Award of the American Concrete Institute.

In 1964, Marcel Broodhaerts showcased his work “Casserole and closed mussels” and stated  ’The bursting out of the mussels from the casserole does not follow the laws of boiling, it follows the laws of artifice and results in the construction of an abstract form’

Andre Paduart (with glasses and hat) in front of architectural model of the Arrow


Postcard showing the Arrow with suspended footbridge, Andre Paduart, 1958
Casserole and Closed Mussels 1964 by Marcel Broodthaers 1924-1976
Casserole and Closed Mussels, Marcel Broodthaers, 1966


Third Phase 70’s and 80’s: Decline of shell structures and folded plates at the Groenendael Hippodrome

In the 70’s the architectural interest in the expressiveness of shells faded. At the same time, the cost of labor involved in constructing shells, became uneconomic and other long-span structural solutions were favored.  To cover the grandstand of a hippodrome near Brussels, Andre Paduart designed and constructed a 13.5m cantilevering folded plate with a thickness ranging from 7 to 12cm only.  The roof had a width of 106m and no expansion joints. The roof is reminiscent of Eduardo Torroja’s (1891-1961) Zarzuela hippodrome and Hilario Candela’s Miami Marine Stadium.  In 2012, these folded plates were demolished.

In 1976, Marcel Broodthaers is buried at the cemetery of Ixelles, Brussels at a distance of 100m to the University Libre de Bruxelles where Andre Paduart taught thin shell theory.

Folded Plate Roof at Groenendael Hippodrome, Andre Paduart, 1980
Tombstone Marcel Broodthaers, Ixelles Cemetary, 1976.

Author:  Sigrid Adriaenssens

I would like to thank Joe Scanlan for co-constructing the storyline and Paul Van Remoortere for providing valuable information.


Espion, B., Halleux, P., & Schiffmann, J. (2003). Contributions of André Paduart to the art of thin concrete shell vaulting. Proc. of the 1st Int. Congr. on Construction History, 829-838.

What I am thinking: Bill Baker at SOM

William F. Baker, also known as Bill Baker, is one of the leading structural engineers of our generation. Baker was the principal engineer of many buildings including the Burj Khalifa (Dubai, 2004)  and the Broadgate Exchange House (London, 1990) and can be considered as the exponent of the innovative structural engineering  tradition cultivated at Skidmore, Owings & Merrill.

Sigrid Adriaenssens: What is the SOM approach to design?

Bill Baker: I’m a structural engineer within an architectural engineering firm, and that makes my position at SOM a bit unusual. Many of the structural engineering firms out there are consultancy firms, whereas SOM does both. SOM is special in the emphasis on integrated design where the architects and the engineers work together from the very beginning before there is any kind of solution or scheme. This process enables us to develop things that work with SOM’s philosophy of design. The interpretation of that philosophy will keep morphing over time, but essentially what one would expect in an SOM building would be three attributes: simplicity, structural clarity, and sustainability. It’s great when a building has all three of those attributes. Those values naturally align with our philosophy as structural engineers as well. We prefer a simple solution to a complex one. We design structures that clearly express their function and have efficient structural systems that minimize the use of materials and minimize embodied carbon. Our aesthetic values and our technical values are the same. It’s not just engineering, it’s an engineering philosophy.

Bill Baker collaborating with architects and engineers on the Burj Khalifa at SOM
Bill Baker collaborating with architects and engineers on the Burj Khalifa at SOM. Photo ©SOM

How do you situate yourself in the tradition of North American Engineering?

I don’t really think of myself as a North American engineer, although I am based in North America. I look around the world for my inspiration. As far as role models, one of the greatest structural engineers that I’ve ever met is Jörg Schlaich, an engineer from Germany. I’ve had the opportunity to work under Fazlur Khan for a brief time, and I’ve studied his work in-depth. The people who I’ve found helpful in my career are both engineers and architects within SOM including Myron Goldsmith, Hal Iyengar, Stan Korista, John Zils, and Jin Kim. Jin Kim was an architect who, on my very first project, came to me and was very upset with something I had designed because I had created a stair that was very ugly. He had admonished me that my job is to design structures that architects would feel bad to cover up. He was a very important mentor to me.

SOM Colleague (Left), Fazlur Khan (middle), and Hal Iyengar (right) in the office
SOM Colleague (Left), Fazlur Khan (middle), and Hal Iyengar (right) in the office. Photo ©SOM

I’ve always had mentors from other firms. Bill LeMessurier was a great mentor to me. I spent time with him at several conferences and would call him when I needed advice on ideas related to the industry. I’ve always had a great relationship with Les Robertson, and I was fortunate enough to work with him when he was a peer reviewer on an early project of mine. We had some very interesting conversations.

However, a lot of my mentors are not necessarily designers. In the UK there is Stuart Lipton, a developer, and Peter Roger, his partner who works on the constructability of a project. They’ve been very influential on my work.

From academia, the writings and lectures of Princeton’s David Billington are very important to me.

As far as what perhaps sets me apart is that I’m a great believer in research. It is very important to me to use research to explore new structural concepts that can lead to new architecture. SOM is very active and consistent with that idea, and we have innovated new technologies and concepts that were not previously known in the profession because of our research. We’ve discovered new understandings of the way structures work, and this enables us to design in different ways. That’s something about SOM that sets us apart from other engineering firms.

Bill Baker in SOM_s Wind Tunnel
Bill Baker in SOM’s Wind Tunnel. Photo © SOM

What is your greatest professional achievement and why?

That’s a tough question. When you say “greatest”, it makes other things secondary. I have a lot of things I’m very proud of, and just like you don’t rank your children, I don’t want to rank my achievements. There are some buildings I’ve been involved in that I’m very proud of, like the General Motors entry pavilion in Detroit; the Exchange House in London that spans the tracks at the Liverpool street station; and the Burj Khalifa of course. I’m also very proud of some buildings that were never built, like 7 South Dearborn, because of the interesting concepts we used to design them.

Broadgate Exchange House
Broadgate Exchange House. Photo © Richard Waite
Burj Khalifa
Burj Khalifa. Photo © Nick Merrick | Hedrich Blessing

I greatly enjoy working with artists. They can table our technical input and use it to inform their art. Our work with Inigo Manglano-Ovalle, James Carpenter, and James Turrell was very satisfying to me.

Gravity is a Force to be Reckoned With by Inigo Manglano-Ovalle
Art Installation by Inigo Manglano-Ovalle titled “Gravity is a Force to be Reckoned With”.

That’s on the project side. On the professional side, I think I’ve been helpful in moving the profession towards a more creative way to design. By explaining what it is we do as far as research and discovering new ideas, I believe we’ve helped the profession to keep moving forward.

Within the profession, it is very important for us to promote a technology-based creative process that leads to new architecture. I’ve worked very hard at that by using the soap box here at SOM to share this knowledge in order for the profession to rise to a new level.

What is your favorite structure and why? Could it be improved and how?

The John Hancock Center in Chicago is my favorite structure because of its clarity, the simplicity, and sophistication. The way it meets the ground, the way it tells its story. How would I improve it? I’d improve it by making the floor-to-floor height a little better. The apartments are a little tight! But overall, it’s a great building. My improvements to it would be fairly secondary.

John Hancock Center
John Hancock Center. Photo © Ezra Stoller

What are Maxwell diagrams and Mitchell frames? Why are they important to you and your work?

For me, Maxwell diagrams (Graphic Statics) help the engineer visualize the forces in a way that no other methodology allows. You can visualize the forces much more clearly. Mitchell frames help you find benchmarks so you know if your solution is efficient by comparing it against a Mitchell structure. They also provide structural geometrics that one may not find using a traditional approach. They are both very important and they both lead to a creative process because they give you feedback that you can, through your intuition, create something new. I don’t think intuition comes from nothing, it is an accumulation of knowledge and experience that leads to new ideas. Having that knowledge can lead you to intuitions that you wouldn’t have otherwise.

What would you change in the education of the next generation of structural engineers?

I would put more emphasis on the theory of structures, engineering mechanics, and the behavior of materials: the true technology of our discipline. These are things that will not change unless you invent new materials. A building code has the shelf life of a banana: it’s going to change and it’s going to morph into something different. However, the underlying physics will stay the same.

What is the use of the future structural engineer? If you go back a long time, you had to understand theory because you could not calculate very much. Today, we’re in a computational age where we use a tremendous amount of brain power to manipulate the “box”.  In the future, computation will be so trivial, where it almost becomes unimportant, but the theory will be the paramount thing that the engineer will bring to design.

Bill Baker studying Burj Khalifa model
Bill Baker studying Burj Khalifa model. Photo: Courtesy of SOM

What question are you never asked and would like to be asked? What would be the answer?

If you had not become an engineer, what would you have become?

An auto-mechanic. Fixing something that’s broken is quite satisfying.


We would like to thank Bill for taking the time to answer our questions, as well as Danielle Campbell of SOM for transcribing the interview. Questions by Sigrid Adriaenssens, further editing by Tim Michiels.

What to see when visiting Cambridge, UK

Our Princeton alum, Anjali Mehrotra, is currently pursuing a PhD in historic masonry structures at the University of Cambridge, UK. We asked Anjali to take us on a campus tour in search of structural surfaces. This is what she showed us.

King’s College Chapel,  1446 – 1515

There is an abundance of vaulted structures in Cambridge, including the main gates of Corpus Christi College, Trinity College and St John’s College, which are also examples of fan vaults and are each adorned with the respective college’s crest.

Corpus Christi College 1353  and St John’s College 1511 gates

Other vaulted structures in St John’s include the cloisters of the neo-Gothic New Court, which were designed by Thomas Rickman and Henry Hutchinson between 1826 and 1831. Around the same time, another architect, William Wilkins, designed the Great Hall and Gatehouse of King’s College.

St John College Cloisters and detail Gatehouse King’s College

Professor Jacques Heyman, former Head of the Cambridge University Engineering Department, is widely considered to be one of the world’s leading experts in cathedral and church engineering. He revolutionized the analysis of masonry structures by translating plastic theory developed for steel design into theorems which could be used for stone as well. His book The Stone Skeleton: Structural Engineering of Masonry Architecture is the seminal work in this matter. His theories have been used for the analysis of various types of masonry structures including arches, spires and vaults, with the latter including Gothic style fan vaults, with perhaps the most famous example being the vault of King’s College Chapel in Cambridge. Built between 1512 to 1515 by John Wastell, the fan vault is 88 m long and 12 m in span, making it the world’s largest.

Professor Jacques Heyman and interior view of King’s College Chapel 1512-1515.

Author: Anjali Mehrotra