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Journal of Civil Engineering and Architecture 14 (2020) 10-19 doi: 10.17265/1934-7359/2020.01.002
UHPFRC Folded Pavilion
Raphael Fabbri1,2, Catalina Francu3, Beatrice Gheno3, Mattia Federico Leone4 and Jenine Principe4
1. Maitre de Conference des Ecoles d’Architecture, ENSA Paris-Belleville, 60 boulevard de la Villette, Paris 75019, France
2. ATELIER MASSE, 14 rue des Jeuneurs, Paris 75002, France
3. ENSA Paris-Belleville, 60 boulevard de la Villette, Paris 75019, France
4. Department of Architecture, University of Naples Federico II, Via Toledo 402, Naples, NA 80132, Italy
Abstract: The aim of the Student Workshop “Material Optimization and Geometric Exploration” (ENSA Paris-Belleville and University of Naples Federico II) is to discover the possibilities offered by new materials, starting from their characteristics. The final goal is to build a synthetic pavilion, which—in the last session—demonstrates ultra-high performances fibre reinforced concrete (UHPFRC) capacities. Designing with UHPFRC requires thinking simultaneously about the geometry, the static, the casting (mainly precast) and the implementation process. The design of the pavilion starts with a widespread geometric exploration using a phylogenetic tree. This approach has the advantage of exploring different designs at the same time without enclosing the creative process in one path. The geometry of the final pavilion is based on a folded surface, called “Yoshimura”, made out of rows of triangles. The profile of the pavilion is bent in order to create a double curvature and so, more stability. The modules are multiplied asymmetrically to minimize the number of the moulds, having at the end just one mould for each row of triangles. The moulds are made with polyethylene terephthalate glycol (PETG) laser-cut sheets which have been folded afterwards. This process has been chosen for both the smooth finishing it delivers and the simplicity of the fabrication process.
Key words: UHPFRC, folded mould, phylogenetic tree, parametric design, design pedagogy, structuralism.
1. Introduction
1.1 “Techno-Evolution” and “Bio-Evolution”
How does technical evolution happen? Although it
uses different ways, “techno-evolution” has been often
compared to “bio-evolution” by historians and
prehistorians as André Leroi-Gourhan, or by
philosophers of techniques as Gilbert Simondon:
“If we propose to juxtapose Invention and Mutation,
Tradition and Transmission of acquired traits, it is not
to take sides, by extension from technological values
to biological values; the complexity of biological
problems is familiar enough so that we can observe
the utmost caution. Biology is going through its
puberty crisis and Technology is hardly vague, but it
is to be expected that in the future the proximity of the
two disciplines will become increasingly clear and
Corresponding author: Raphael Fabbri, architect, maitre de
conference, research fields: UHPFRC, advanced geometry, parametric design, pedagogy.
that, through the confrontation of the two series of
creations of Nature and the creations of Human
Industry, we will reach a deeper understanding of the
general phenomena of Evolution.” [1].
But both have noted the necessity to “objectify”
(“Objectiver” in French) the process of technical
evolution and not to reduce it to a purely biological
one:
“The classification is made according to specific
modalities that distinguish the genesis of the technical
object from those of other types of objects: aesthetic
object, living being. These specific modalities of
genesis must be distinguished from a static specificity
that could be established after genesis by considering
the characteristics of the various types of objects: the
purpose of using the genetic method is precisely to
avoid the use of a classifying thought occurring after
genesis to divide all objects into genera and species
appropriate to speech.” [2].
It is important to note that “techno-evolution” does
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not take place through DNA transmission but through
“structural re-organisations” [2] created by humans.
These “designers” are all “located” in the social world
of the human production. Then the selection process is
dependent on social factors.
In both cases, the evolution can be separated
conceptually in two phases: the “structural
re-organisation” and the “selection process”. In
biology, the “structural re-organisation” takes place
through the combination of alleles and through
mutations, while the “selection process” is based on
the organism’s capacity to survive and to transmit its
own genetic heritage. In the field of technical science,
the “structural re-organisation” (in its broad meaning)
is conceived by designers as a strategy to deal with
problems, while the “selection process” is a
consequence of the convergence process, which is a
progressive assimilation of all the project
requirements. It is called “Concrétisation” by
Simondon:
“Like in a phylogenetic lineage, a defined stage of
evolution contains within it dynamic structures and
patterns which are at the heart of the evolution of
forms. The technical being (l’être technique) evolves
through convergence and adaptation to oneself; it
unifies inwards according to a principle of internal
resonance.” [2].
The resulting configuration is called “technical
object”, conceptually defined by its “structural
organisation”, or using the words of the American
architect Louis I. Kahn, by its “Form” (in contrast to
its Design. “All the spoons have the same Form, but
each spoon has a different Design” [3]).
1.2 Exploration in Building and Architecture Field
In the field of building and architecture, the phrase
“technical object”, widely used in the industrial sector,
is usually replaced with “typology” or “construction
system”. When a designer (an architect, an engineer or
a craftsman) chooses a typology or a construction
system for a project, they usually work by induction
and analogy: they study something similar that has
already been done. Making a choice through analysis
and deduction, which means starting with all the
requirements of the project and ending with the
technical solution, is very unusual. This fact is due to
the time-efficiency of the “Concrétisation” process.
We can observe it in the industrial sector too: for
example, when a technician designs a motorized
vehicle, he starts from the “structural organisation” of
the existing cars or trucks, instead of defining all the
requirements and then trying to find a way to fulfil
them.
Although the induction method saves time, it has
two limitations:
Are the existing typologies the best technical
solutions available?
How to proceed with a new material or with a
new problem?
We already talk about the first limitation in a
precedent research [4]. The second one is the topic of
this research, focussing on the ultra-high performances
fibre reinforced concrete (UHPFRC). As academics
and designers, we can hardly act on the “selection
process” of “Concrétisation” (resulting from complex
social forces), but we can work on the “structural
re-organization” by questioning old configurations and
proposing new ones.
1.3 The Workshop “Material Optimisation and
Geometric Exploration”
The UHPFRC is a new material whose
characteristics allow new geometries [4]: smooth
shapes due to the absence of passive reinforcements,
precise finishing due to the ultra-thin aggregates, and
flat cross-sections due to the high strength. Designing
with UHPFRC requires the designer to think
simultaneously about the geometry, the static, the
casting process (mainly precast) and the
implementation. The aim of the workshop “Material
Optimisation and Geometric Exploration” (ENSA
Paris-Belleville & University of Naples Federico II) is
UHPFRC Folded Pavilion
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to discover the possibilities offered by new materials,
through exploring their potential [5]. During the last
session of the workshop we focussed on the UHPFRC.
After presenting the material, the work starts with a
widespread exploration, using phylogenetic trees. The
work continued by specifying the design according to
the “rules” of the material. The final goal is to build a
synthetic pavilion, which demonstrates UHPFRC
capabilities. This approach has the advantage of
exploring at the same time different designs,
questioning the “structural organisation” without
narrowing the creative process in one path.
2. Design Phase: Widespread Exploration
2.1 Organisation
The workshop is divided in two phases: the design
phase, hosted in Naples, and the building phase, in
Paris.
The design phase starts with a presentation of the
material UHPFRC: its history, its mechanical
behaviour, the casting process and the fabrication of
mould. The students are then split in 5 bi-national
teams, each of whom focused on one kind of surface:
ruled surface;
revolution surface;
reciprocal frame;
folded surface;
sweeping surface.
To promote a widespread exploration and to avoid
the connatural fascination for a specific design, each
group has to propose 24 small designs, according to a
phylogenetic diagram.
2.2 The Phylogenetic Diagram
The phylogenetic tree is firstly a tool of
classification, used in biology to show the
evolutionary relationships among various species or
other entities. Each branch split-up is based upon
similarities and differences in the physical or genetic
characteristics of the species analysed—the closer the
split between two organisms, the more related they are;
the further the split is, the less related they are. All life
on the earth is part of a single rooted phylogenetic tree,
indicating common ancestry (the tree of life). The
linguistic field defines rooted phylogenetic trees to
show the common origins of the languages (as the
well-known phylogenetic tree of Indo-European
language). Although the scientific validity of this last
diagram is largely discussed, the linguists consider it a
tool for understanding the evolution of languages.
Unrooted phylogenetic trees (without common
ancestry) are today used in the fields of logic,
computer science and taxonomy. Each branch split-up
represents a level of classification. In Architecture,
Foreign Office Architects (FOA, founded by Farshid
Moussavi and Alejandro Zaera Polo), frequently uses
phylogenetic trees to classify their own projects [6]
and to present the different structural organisation of
historical buildings [7]. In their opinion, the
phylogenetic tree is not only an ex post representation
graph, but also an ex ante generative tool. A good use
of phylogenetic trees as a generative tool was made by
the architect George L. Legendre. In his book [8],
Legendre uses a phylogenetic tree of different kinds of
pasta to determine their parametric equations. The
phylogenetic tree of pasta has four levels of
embranchments: (1) the longitudinal profile (twisted,
helicoidal, pinched, bunched, straight, sheared or
bent); (2) the cross-section (solid, hollow or
semi-open); (3) the surface (smooth or striated) and (4)
the edges (smooth or crenelated). The first level gives
the general typology of the parametric equation, and
the other three levels add more complexity to the
equation. The parametric equations might seem too
complex to be quickly understood at a first glance but
on a closer look, we understand that they are built by
the different levels of the phylogenetic tree.
From a tool of classification, the unrooted
phylogenetic trees are becoming a useful exploration
tool, able to show all the combinatorial possibilities.
In this research, the phylogenetic tree is used as a tool
for the exploration of structural re-organisations.
UHPFRC Folded Pavilion
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Using the phylogenetic tree (see Figs. 1 and 2), each
student group (see above) briefly designs 24 pavilion
proposals, one for each final branch of the tree. The
bifurcations of the phylogenetic tree are organized in
three levels: at first the “composition” (through the
“shape generation” process the pavilion can be
designed as a unique surface or as an addition of
single elements), then the “static scheme” (arch, side
wall, dome and funicular) and finally the “membrane”
(continuous, openwork or gridshell/wireframe
membrane).
Afterwards, each group decides to develop
specifically one of the final branches. As we do not
have the space to comment all 120 (24 × 5 groups),
only the five pavilions that were developed are placed
at the end of the phylogenetic tree (see Fig. 2). For
each of them, the morphology, the static scheme, the
assemblies and the implementation have been defined.
3. Building Phase: Synthetic Pavilion
3.1 Morphogenesis
The final pavilion incorporates principles from
every group and puts the UHPFRC’s capacities to the
test. The first group, “Rositalian Spiral”, offered the
form of two spirals entwined in plane—a kind of
“rolling in itself” effect—cited in the synthetic
pavilion’s tendency to turn inwards. The “FRA NA”
group’s design is responsible for the folding pattern as
well as for the casting process. “Pentathing” inspired
the polygonal division of the initial surface as well as
the manner of component assembly. The
function—seating with sunshade incorporated—was
added into the final design from the concept of the
group “Micro Cosmos” while the group “Spritz”
offered the idea of using adaptive moulds, as well as
the courtyard implementation. Fig. 2 showcases each
of the five designs and their relationship on the
branches of the phylogenetic tree for a better
understanding of the final pavilion as well as out of a
need for transparency in terms of the design process.
The geometry of the final pavilion is based on a
folded surface, called “Yoshimura folded” or
“Whirlpool”, made with rows of triangles. The profile
of the pavilion is bent in order to give it a double
curvature and so, more stability. The modules are
multiplied in axisymmetric rotation to minimize the
number of the moulds, having at the end just one
mould for each row of triangles (see Fig. 3).
The vertices of the triangles are cut to avoid sharp
angles. The centre of the element is open, for both
light and weight reasons.
Figs. 4 and 5 present the main steps of the
morphogenesis:
(1) The 10 basic triangles generated by the bending
of the Yoshimura folding pattern;
(2) The cut of vertices of the triangles;
(3) The contact surfaces between blocks;
(4) The internal void of the blocks;
Fig. 1 The three levels of bifurcations in the phylogenetic tree.
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Fig. 2 The whole phylogenetic tree with the five projects explored by each team.
UHPFRC Folded Pavilion
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Fig. 3 Repetitive triangles in the “basic” Yoshimura folded (left) and in the “bent” one (right).
Fig. 4 Morphogenesis: (1) basic triangles, (2) cut of vertices, (3) contact surfaces between blocks, (4) internal voids.
Fig. 5 Morphogenesis: (5) holes for the bolts, (6) axisymmetric rotation, (7) mirror and trimming.
(5) Holes for the bolts;
(6) Axisymmetric rotation;
(7) Mirror and trimming.
3.2 Casting Process
The moulds are made out of laser-cut polyethylene
terephthalate glycol (PETG) sheets which have been
folded into the necessary shape (Figs. 6 and 7). This
process has been chosen for both the finishing and the
simplicity of fabrication. The PETG sheets are easy to
fold and clean, but they have weak bending stiffness,
so they had to be reinforced by wood boards cut to
size. The internal void in the overall shape is made
with the help of a polystyrene block. The structural
UHPFRC Folded Pavilion
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strength of the pavilion lies in the contact surface
between elements, necessary to sustain load forces. To
ensure the stability of the aforementioned connection,
we used (8Φ × 130 mm) bolts that traversed both
pieces and were fixed into place by nuts (Fig. 8). The
mould required us to protect the mobility of the bolt
while still casting its void in the piece; therefore, we
chose to use a Vinyl/PVC flexible tube (as long as the
thickness of the element) to protect it.
The UHPFRC used for the casting is DUCTAL
NAW3 from LafargeHolcim. The mould was
externally watertight, but sometimes concrete flowed
between polystyrene and PETG. To solve this issue,
we added a compressed foam-joint in-between. The
mould has been slightly improved during the 5 days of
casting, but the general concept has been maintained for
Fig. 6 Pictures of the moulds.
Fig. 7 First cast elements.
Fig. 8 Pictures of the cast elements and the assembly.
UHPFRC Folded Pavilion
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its efficiency.
3.3 Implementation
The pavilion was implemented in April 2019 during
the second phase of the workshop with the help of the
students. After the realization of the wood base, the
construction started from the pre-assembly of the
triangles which would have been anchored to the
ground. They were fixed together using two bolts. A
cork sheet was placed in between the connecting
surfaces, which were folded to block the shear and to
guarantee good contact. The actual implementation
had to proceed symmetrically, in order to conclude the
building process with the keystone (also to exploit the
scenic effect). After setting the first pieces of the
principal arch and the double triangles immediately
near them, the construction started to become more
complex. Despite it, it was possible to build it without
any temporary support elements, besides some
movable wood trusses. Immediately before putting the
keystone, the smaller pieces without any structural
function were rapidly installed. After removing the
temporary supports, the pavilion had a small
adjustment, followed by an uneasy but harmless
creaking. Without considering the wooden base
(whose designing and building process took two days),
the construction of the pavilion, pre-assembly
included, lasted for 12 hours with a maximum of 8
people who worked on it.
4. Final Pavilion and Future Works
The pavilion was built in the interior garden of
Ecole Nationale Supérieure d’Architecture de
Paris-Belleville (Figs. 9 and 10). The experience made
us think further, to what future research might
uncover, and a few ideas that seemed important are
building methods that do not involve
shoring—through a design in which the gravity centre
is always kept inside the cupola-shaped structure’s
projection on the ground. Nowadays, repetitive
geometries are used for reducing the moulds’ cost
in precast building [9] so, an important issue to further
Fig. 9 Render of the final pavilion (left) and picture in May 2019 (right).
Fig. 10 Pictures of the final pavilion in May 2019.
UHPFRC Folded Pavilion
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explore could be the optimisation of adaptive PETG
folded moulds to meet the requirements of both
geometry and cost optimisation. In other words, the
aim is to achieve the optimal balance between variety
and practicality in the building process, because the
first one makes way for innovation while the latter
makes it possible.
UHPFRC has a huge shaping capacity, as its liquid
form and the absence of passive reinforcements permit
a large degree of imagination. One of its biggest
advantages is its high load-bearing capacity, even
when cast in thin dimensions. This, together with its
relatively light weight, makes it much easier to shape
than stone, both in its liquid and precast form; even if
we must remember that the issue of contact surface has
to be further developed. This need emerges from the
necessity to fix the degrees of liberty in order to
better control the global shape. The precision and the
strength of the connections are crucial for this kind of
pavilion.
The pedagogical methods and the research carried
out during the workshop “Material Optimization and
Geometric Exploration” are both experimental and
structuralist. Since the 2000s, experimental
pedagogical methods are spreading in architecture and
engineering universities, not only because of the
development of digital fabrication, but also because
they provide an important complement to other kinds
of teaching. The students are involved in collaborative
research leading to a final collective production.
These new teaching processes must be completed by
theoretical background and analytical feedbacks,
producing real experimentation and not only a simple
experience. Although structuralism is not as studied as
during the 60s and the 80s, it is an effective method of
exploration and creation. By focusing on the
structures, the student develops a creativity that
touches the essence of the technical objects and opens
up to possibilities for evolution.
Last but not least, we would like to touch upon the
new directions UHPFRC might open in the realm of
building and architecture. It is important to note that
with each new discovery we are bound to develop a
way of using it without falling into the mannerism of
rebuilding canonical shapes with materials that offer a
much wider spectrum of possibilities. We are firmly
advising against building with concrete following the
logic of the brick: we suggest that architects, as well
as engineers, would have a lot to gain from
approaching this new material through a critical and
curious lens that will most certainly unleash much
more richness than if they stick to the known. Today
we find ourselves in the same position of Louis I.
Kahn when he asked the brick what it wanted to be,
more than half a century ago: “You say to a brick,
‘What do you want, brick?’ And brick says to you, ‘I
like an arch’.” We have to understand this material
and know its answer to our question.
Acknowledgements
We would like to express our gratitude to Ductal
Team, to the ENSA Paris-Belleville, to the
Department of Architecture of the University of
Naples Federico II and to the French Ministry of
Culture for their support.
Special thanks to all the students and all the
teachers of this workshop:
Nunzia Ambrosino, Ata Gun Aksu, Iris Andreadis,
Maher Ben Hamed, Enrico Corvi, Thibaud de Zuttere,
Davide Ercolano, Olmo Galletti, Martin Gatto, Sarah
Husein, Elioth Jeantet, Daniele Lancia, Simona
Makoski, Simone Muscio, Aurora Naddeo, Giovanni
Nocerino, Bianca Pagano, Arianna Palumbo, Simone
Piccolo, Manuele Puopolo, Martina Pizzicato, Sergio
Pone, Alexandra Runcan, Edoardo Schettino,
Mariagrazia Serafino, Camille Vouin, William
Wattequant.
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