Shell Structures: Lessons for Sustainable Construction in Developing Countries, Esquemas y mapas conceptuales de Derecho

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Shell Structures from

Catalan to

Mapungubwe

Lessons from Structural Efficiency for Sustainable Construction in

Developing Countries

Kavinda Isuru Nanayakkara

1. INTRODUCTION

In a world moving towards a sustainable earth, the developing world is faced with the dilemma of rapid expansion of housing and infrastructure needs on the one hand and the constraints of sustainability on the other. However, a closer look at local strengths and technology elsewhere can lead to creative solutions. Shells are a more efficient structural form than the widely used column-beam frames, which make use of bending strength and hence underutilize the structural capacity of materials. Superior structural efficiency allows for shell structures to be lightweight and thus reduce the material demand. The wide range of possible material solutions – from compressed earth to concrete - allow for an appropriate local material to be used in the realization of the structural form. Shell structures are by no means a modern invention. Evidence of the earliest vaulted structures come from Mesopotamia in 3000BC; a 5000-year-old Mesopotamian burial chamber having a barrel vault of approximately 1 m span is in display at the Berlin Museum of Prehistory and Ancient History (Kurrer, 2008). The Roman arch, the bridges and cathedrals in Europe built during the renaissance, the modernisme movement in Barcelona and Guastavino vaulting, which spread in the east coast of the USA, have all left us with a rich collection of form-resistant structures. The more modern inclusions to this collection are Hassan Fathy’s reinvigoration of Nubian technique, Heinz Isler, Frei Otto and Luigi Nervi’s compression only shells followed by Jacque Heyman’s safe theorem giving a systematic approach to design compression only shells. The current study looks at both the traditional technologies (and adaptations thereof) and explores new frontiers in lightweight shell construction to scope out potential future growth. An understanding of socio-cultural impacts of these structures, technologies and materials give a better perspective on how technology can be appropriated to different local contexts. This brief report includes knowledge gathered from travels to India, Europe and the USA; the former two being funded by the Pai Lin Li Travel Award presented by the Education Trust of the Institution of Structural Engineers, UK. The travels relevant to this report include visits to the following places.

2. DESIGN PHILOSOPHY: A CASE FOR SHELL STRUCTURES

Arch as a structural form was necessitated when beams were no longer able to bridge increasingly longer spans. Vaults and domes too may have been evolved due to such needs, but some historians and architects suggest that domical roofs used in cathedrals are suggestive of heaven or the realm of gods. Nonetheless, vaults and domes (the most common shell geometries from early days) were used for different functions and out of different materials in different places across the globe. 2.1. Nubian Technique The tradition of earthen structures as practiced by the Auroville Earth Institute (AVEI) is not necessarily a traditional Indian technology but rather a mindful adoption of the Nubian technique, as popularized by Egyptian architect Hasan Fathy. However, significant improvements to design methodology, production of material and construction has taken place at AVEI during its 30 years of existence. Nubian technique has originated from Nubia in south of Egypt and the famous vaults of the granaries of the Ramesseum at Gourna, Egypt are testament to the success of this technique. The basis of the Nubian technique is that the blocks adhere to each other with an earthen binder (Figure 2. 1 ). The adhesion is achieved when the dryer blocks draws in water by capillary suction and the clay components of the soil acts as an adhesive to bind the blocks. Traditionally, the Nubian technique requires a back-wall to mark the curve and ‘lean’ the first course of blocks. The vault is built as a sequence of arches slightly leaning on each other. The binder is a silty-clayey soil (from the Nile) and a binder layer of 10 – 15 mm is used with sun dried blocks. Figure 2. 1 - Nubian vaulting technique. [Image source: Davis & Maini, 2016]

Figure 2. 2 - Auroville Earth Institute. (^) Figure 2. 3 - Auroville Visitor Centre. Nubian technique can also be used to build circular domes with a compass to guide the geometry. At Auroville they have developed a series of compasses to be used with various geometries. A further development at Auroville is the ‘free-spanning’ technique. The premise here is to determine the sequence of construction in such a way that partially built structure always has a safe load path. This is further discussed in Section 4.2. The designs and constructions done by AVEI include buildings at Auroville Earth Institute (Figure 2. 2 ), Auroville Visitor Centre (Figure 2. 3 ), Gayathri Dome in Auroville, Dhyanalinga dome and Sharanam conical vault. 2.2. Catalan Vaulting In contrast to the heavy and thick masonry shells following from Nubian technique, Catalan vaulting (or Guastavino vaulting as referred to in the USA) uses multiple layers of very thin tiles (usually 3 layers of 15 - 20 mm thick tiles- see Figure 2. 4 ). Catalan vaulting too is a free spanning technique, using guides to define the geometry in space. This makes it an interesting technique to be used with free-form shells such as the one built in Valldaura Labs (Figure 2. 5 ), by a group of students from the Polytechnic University of Catalonia, Barcelona. The first layer of Catalan vaults is built in space with a fast setting gypsum mortar. The subsequent layers are built with the first layer acting as the form work. There are many examples of Catalan vaulting in both Barcelona and in the USA. The examples in Barcelona includes Teatre La Massa (Rafael Guastavino – Figure 2. 6 ), factory building in Terrassa (Lluís Muncunill i Parellada – Figure 2. 7 ), Palau de la

Figure 2. 7 - Catalan vaulted roof of the factory building at Terrassa (now Museu de la Ciència i de la Tècnica de Catalunya) designed by Lluís Muncunill i Parellada. Figure 2. 8 - Catalan vaulted ceilings of the Palau de la Música Catalana designed by Lluís Domènech i Montaner. Figure 2. 9 - Catalan vaulted roof of the Restaurant en Ville, Barcelona designed by Rafael Guastavino. The image on the left is an early example of the herringbone pattern being used in doubly curved Catalan vaults.

Figure 2. 10 - Exposed and unexposed vaulted ceiling / floors around the city of Barcelona. Figure 2. 11 - Guastavino vaulted (Catalan vaulting) ceiling/ slab system in Boston Public Library.

Figure 2. 15 - Guastavino vaulted ceiling at New York Chamber Street City Hall Building. Figure 2. 16 - Guastavino vaulting in the Queensboro Bridge, New York City. Figure 2. 17 - Guastavino vaulted ceiling at the Oyster Bar in the Grand Central Station. This survived a major fire in 1997 with delamination of some tiles being the only damage caused.

Figure 2. 18 - Guastavino vaulted walkway in a building in Vesey Street New York City. This structure is directly opposite to the World Trade Centre and survived the impact from debris during the collapse of the twin towers in September 2001. 2.3. Gaudi’s forms following forces With an understanding of flow of forces, gained from his physical models, Antonio Gaudi was able to use the full canvas of the three dimensional space and produced some wonderful structures in doing so. Park Güell houses simple examples of forms following forces (Figure 2. 19 ), whereas La Sagrada Familia (Figure 2. 20 ), Colonia Güell (Figure 2. 21 ), Casa Milà (Figure 2. 22 ) and Casa Batlló (Figure 2. 23 ) depicts more elaborate expressions of forms following forces. Figure 2. 19 - (a) a domed roof slab, (b) a vaulted viaduct and (c) tilted columns - all forms following forces- at Park Güell by Antonio Gaudi. (a) (b) (c)

Figure 2. 21 - Ribbed and vaulted roofs of Catalan tiles at the crypt in Colonia Güell, designed by Antonio Gaudi. Figure 2. 22 - Ribbed and vaulted roof structure at the attic of Casa Milà, designed by Antonio Gaudi. Figure 2. 23 - Ribbed arches in Casa Batlló, designed by Antonio Gaudi.

2.3. Similar yet different All three types of technologies of shell structures discussed above does the same fundamental thing; they carry loads primarily in compression. However, there are interesting differences in (i) how they account for variable loading and (ii) how the lateral thrusts at supports are resisted. 2.3.1. Accounting for variable load The heavy Nubian vaults have a much higher self-weight in comparison to variable loads. Also, these shell structures are typically used as roof structures rather than slab systems. Thus, the self-weight itself is the significant loading and the effects of variable action can be reasonably accounted for by having a safety margin on the thickness of the shell. Figure 2. 24 - (a) Catalan vaulted slab system in an old weaving mill (currently being renovated as a museum) in Vilassar de Dalt, (b) a cross section of the Catalan vaulted slab, and (c) (d) a partially demolished part of the slab showing the vertical stiffeners in the hollow slab. Catalan vaults are used as slab systems (Figure 2. 24 ) and have a much thinner shell. As such the variable loading is a significant factor for the safety of the structure. It is observed that the Catalan vaulted floor slabs account for the variable loading by having vertical stiffeners (see Figure 2. 24 c and d). Furthermore, Rafael Guastavino has extensively used doubly curved thin shells as slab systems (Figure 2. 11 ) to give (c) (a) (b) (d)

Figure 2. 26 - (a) Stuttgart SmartShell and (b) its actuator system, constructed at ILEK, University of Stuttgart. 2.3.2. Resisting lateral thrust The heavy masonry structures observed in Auroville (Nubian technique) and Barcelona use masonry buttresses ( Figure 2. 28 ) to safely carry the large horizontal thrusts created. In contrast, light weight Catalan vault systems use steel tie rods (see Figure 2. 24 and Figure 2. 27 ) to carry the horizontal thrusts. Figure 2. 27 - Steel rods taking the horizontal thrust of Catalan vaults in a restaurant in Vilassar de Dalt. Figure 2. 28 - Making use of buttressing to resist the horizontal thrust (in absence of tie rods) of Catalan vaulted structure, at University of Massachusetts. These tie-back techniques are observed in more modern projects done by BRG. The Armadillo Vault uses steel support plates tied back with steel rods (Figure 2. 29 ) so as not to damage the historical floor of the exhibition hall. The ETH Zurich Pavilion for the 2015 Ideas City festival in New York did not use any tie back (Figure 2. 30 ). The lighter (a) (^) (b)

weight of the vault (due to it being built of hollow blocks made from compressed tetra pack panels) meant that the stability of the stack of timber pallets supporting the vault can be guaranteed by weighing down the timber pallets with ballast loads. Additionally, the pallets were bound together to act as a single unit. Figure 2. 29 - Armadillo Vault designed by BRG. [Image source: BRG http://block.arch.ethz.ch/brg/content/project/armadillo-vault-venice-italy] Figure 2. 30 - Pavilion designed by BRG for the Ideas City Festival in New York 2015. [Image source: BRG http://block.arch.ethz.ch/brg/project/eth-ideas-city-pavilion-new-york-ny-usa].

would always give a lighter weight solution than a compression only solution (e.g. compression shell) although the latter still gives a positive Bic value. This stand to show that compression-only shells are not the end of the path for optimizing material usage- there can be lighter weight solutions if one intends to look for. However, considering the material at hand (e.g. materials with low tensile capacity) or other constraints, compression-only solution will be the best one can aim for.

3. DESIGN METHODOLOGY: FROM INTUITION TO INFORMATION

AGE

The structural analysis of compression only forms have evolved through the years. But all the methods of analysis observed during this study were based on one fundamental idea; Robert Hooke’s observation of hanging chain – “as hangs the flexible cable, so but inverted stands the rigid arch”. 3.1. Physical models 3.1.1. Antonio Gaudi Physical models are the most fundamental manifestation of Robert Hooke’s observation. Antonio Gaudi has extensively used physical models (Figure 3. 1 and Figure 3. 2 ), which are daring in their size and complexity, as are his realized structures. Hanging chain models are more complex manifestations of Robert Hooke’s hanging chain. Different weights are attached to nodes to represent the loadings on the structure, due to self-weight or otherwise. Unlike the Heinz Isler’s models described later, the hanging chain model is not rigidified, but the inversion is done on paper with geometry measured from the hanging chain model. A glass mirror was used to look at the inverted shape to get a sense of the shape generated. 3.1.2. Heinz Isler Heinz Isler’s physical models are much simpler. The scale model in Figure 3. 3 is a hanging chain model rigidified in plaster of Paris (gypsum plaster) which also includes cables to resist the horizontal thrusts. The simplicity in his models made sure that these structures can be repetitively used in different projects. The model was built as a form-finding model for the Norwich Sports Centre roof structures. This roof structure was used for many tennis court and swimming pool roof structures by the architects

Haus + Herd of Herzogenbuchsee (Chilton, 2000). The tennis court complex in Solothurn has a similar roof structure (Figure 3. 4 ). The model in Figure 3. 5 is a plastic shell prototype used as a load testing model for the design of concrete shell roof structure of Dübendorf Air Museum. The model in Figure 3. 6 is used to show the effect of shear deformable nets in giving clear doubly curved surfaces, whereas a cloth which has some shear resistance will show wrinkles. Figure 3. 1 - Hanging chain model of La Sagrada Familia. Figure 3. 2 - A replica of the hanging chain model of the crypt in Colonia Güell.