Marisela Mendoza and Juan Ignacio del Cueto Ruiz-Funes

Preservation and conservation of Felix Candela’s historic concrete shell: Los Manantiales restaurant.

Marisela Mendoza1 and Juan Ignacio del Cueto Ruiz-Funes2 1. Course Leader MArch, School of Architecture Design and Built Environment, Nottingham Trent University; 2. Professor in Architecture, Faculty of Architecture, Universidad Nacional Autónoma de México

Introduction

Félix Candela Outeriño was born in 1910 in Madrid. Candela studied architecture at Escuela Superior de Arquitectura, Madrid and completed his studies in 1935. It was during his time at school that he became acquainted with thin-shell concrete structures. During the Spanish Civil War (1936-1939), he enrolled in the Republican Army as a volunteer [1] and in 1939 he fled to Mexico as a political refugee. Almost ten years after his arrival in Mexico, Candela co-founded the construction company Cubiertas Ala. During the tenure of Cubiertas Ala Candela mastered the design and construction of thin-shell concrete structures, in particular the hyperbolic paraboloid concrete shells or commonly known as ‘hypars’. The use of the hyperbolic paraboloid geometry to design concrete shells was not new in the realm of engineering and architecture and Candela had researched the work of other experts in the field to inform the design and structural analysis of his shells [2]. However, what can be attributed to Candela is the ingeniousness and inventiveness in the construction process of ‘hypar’ concrete shells . Once the geometry of the shell was determined and the structural analysis verified, its construction techniques and construction management required a skillful group of workers to place the formwork, lay out the steel work, pour the concrete by hand and the careful formwork removal.

In 1958, and commissioned by the Joaquín Álvarez Ordóñez, Candela built Los Manantiales restaurant, one of his most famous thin-shell concrete structures on the banks of the Xochimilco canals. To this date Xochimilco is primarily a recreational area in the Southern part of Mexico City and in 1987 it was listed as UNESCO World Heritage Site. Formed by an eight-sided groined vault, Los Manantiales concrete shell covers an area of 900 square meters, and which represents the best of many examples of ‘free edge’ concrete shells built by Cubiertas Ala.

Design and construction of Los Manantiales

Lake Xochimilco was one of the five pre-Hispanic lakes in the ancient valley of Mexici City was the core of the chinampa agriculture site (man-made floating agricultural gardens built during the Aztec ruling). However, destruction of dams and gates after the Spanish conquest of Mexico led to the decline of agriculture and Lake Xochimilco gradually dried. Although on a smaller scale, agriculture activities continued on the banks of the remaining canals and by the mid-twentieth Century the canals became an important recreational site for trajineras

577 Preservation and conservation of Felix Candela’s historic concrete shell: Los Manantiales restaurant (gondola-like) weekend rides [3]. To service the recreational site a wood-built restaurant on the banks of Lake Xochimilco was constructed in 1938 (Fig.1).

Figure 1. Los Manantiales wood-built restaurant, 1938. Courtesy of Archivo de Arquitectos Mexicanos (AAM-FA UNAM)

In 1957, the wood-built restaurant was destroyed in a fire and the owners asked the architect Joaquín Álvarez Ordóñez to rebuild it using non-flammable materials. The young architect Álvarez Ordóñez (25 years old at the time) proposed a concrete roof and contacted Candela to collaborate with him. By that time Cubiertas Ala had already built experience and reputation as experts in the construction of thin-shell concrete structures in Mexico. Furthermore, Candela was very excited about this project as it was a great opportunity to put in practice one of his most recent achievements, the free-edge concrete shell. In 1953 and in collaboration with the architects Enrique de la Mora and Fernando López Carmona, Candela built his first groined vault for the Stock Exchange Market (Fig.2).

Figure 2. Stock Exchange Market, Mexico City, 1953. Courtesy of Archivo de Arquitectos Mexicanos (AAM-FA UNAM).

578 Marisela Mendoza and Juan Ignacio del Cueto Ruiz-Funes

In this groined vault Candela achieved the most-desired smooth surface that the architects were looking for by concealing the border-beams. However, Candela was convinced that border beams could be omitted, and he began working on different structural design solutions and construction strategies to achieve a free-edge-beam hypar groined vault. Three years later, in 1956, Candela built his first free-edge ‘hypar’ concrete shell for the church of San Antonio de las Huertas in 1956 also in collaboration with De la Mora and López Carmona (Fig.3).

Figure 3. San Antonio de las Huertas Church, Mexico City, 1956. Courtesy of Archivo de Arquitectos Mexicanos (AAM-FA UNAM).

Although Candela was not able to provide a full structural analysis for this free-edge hypar concrete shell, the built structure demonstrated that Candela’s success was a combination of his vast knowledge and intuition [4]. Another example of free-edge hypar shells built by Candela in 1957 was at Hotel Presidente in Acapulco and in collaboration with the architect Juan Sordo Madaleno [5].

579 Preservation and conservation of Felix Candela’s historic concrete shell: Los Manantiales restaurant The shape for Los Manantiales restaurant followed the trend of the recently developed groin vaults built by Candela and was conceived as an octagonal groined vault composed of four intersecting hypars (Fig.4).

The groined vault covered a span of 32.4 meters and the groins were stiffened using V-beams. These V-beams were specially designed to integrate smoothly and to follow the slenderness and curves of the concrete shell. The free edge form was achieved by ‘cutting in outward-tilting planes and the resulting perimetral arches have the shape of hyperbolas’ (Fig.4), [6].

Figure 4. Felix Candela’s architectural drawing for Los Manantiales restaurant. Source: Colin Faber, The Shell Builder.

The site where the thin-shell concrete for ‘Los Manantailes’ restaurant was built sits on the Lake Zone of Mexico’s City Seismic Hazard Maps. Mexico City is well known for its high seismic activity, those originated in the subduction zone of the Pacific Ocean, where the Cocos plate subducts the North America plate [7]. Although the epicentres of some of these earthquakes have originated at a distance of more than 250 km far away they have been disastrous to the city’s built environment. The apparent reason for this seems to be ‘a combination of frequency content, regional geological and structural features which can produce huge amplifications and very long-time durations in Mexico City’ [8]. The seismic hazard maps of Mexico City divide the basin in three zones: The Lake Zone (I), the Transition Zone (II) and the Hill Zone (III) of which the Lake Zone is at greatest risk due to the presence of lacustrine clays. The mapping of Candela’s structures developed by Mitchels [9] against the three basin zones of Mexico City demonstrates that Los Manantiales thin-shell concrete was built in Zone I (Fig.5).

580 Marisela Mendoza and Juan Ignacio del Cueto Ruiz-Funes

Figure 5: Map of Félix Candela’s structures in Mexico City against the three seismic hazard zones of Mexico City. Image courtesy of T. Michiels.

The shell formwork was made with 1.27cm wide tongue-and-groove timber boards and placed according to one generating system. At the time Candela built Los Manantiales, he had already established a standard thickness of 4cm for shells: ‘The Standard thickness of 1½ inches has been found the most convenient for these shells, since its concreting does not require special care, and ordinary gravel, up to 1 inch, can be employed in the mix.’ [10]. Surveys conducted of most groined shells that candela built at that time showed that they were built with a thickness of at least 5cm.

581 Preservation and conservation of Felix Candela’s historic concrete shell: Los Manantiales restaurant Steel reinforcement consisted of a 5/16-inch-diameter mesh of steel bars spaced at 10 centimeters (Fig 6). The five-centimeter-thick edge of each intersecting hypar was reinforced with two 16 mm (5/8 in) bars following the sinuous perimeter of the shell.

Figure 6. Los Manantiales during construction, steel reinforcement. Image courtesy of Archivo de Arquitectos Mexicanos (AAM-FA UNAM).

Concrete pouring of Los Manantiales shell was made by hand using buckets (Fig.7). The shell’s foundation consisted of umbrella footings that were linked with 1-inch-diameter steel tie-bars to resists lateral thrusts [11]. Umbrella footings had been pioneered by Candela, first used in 1953 at Las Aduanas project (Fig.7). Furthermore, and to secure the continuous curvature, the original sharp v-shape of the supports (where the groins met) was modified to integrate into the curve of the shell [12].

Figure 7. Umbrella footings, Las Aduanas project, Mexico City, 1953. Image Courtesy of Department of Rare Books and Special Collections, Princeton University Library

582 Marisela Mendoza and Juan Ignacio del Cueto Ruiz-Funes

Figure 8. Los Manantiales during construction, concrete pouring. Image courtesy of Archivo de Arquitectos Mexicanos (AAM-FA UNAM).

Current state of the shell, conservation and preservation.

The 7.1 magnitude earthquake that shook Mexico on September 19th, 2017 had devastating effects in the central and south areas of Mexico City including Xochimilco borough where Los Manantiales restaurant was built. As illustrated in Fig. 9 Los Manantiales concrete shell was significantly affected, buckling occurred on one the eight hypars composing the groined shell and altering its form, thus compromising the structural behaviour of the shell (structural integrity of hypar shells is by and large dependent on the integrity of their form).

Figure 9. Buckling on the intrados of Los Manantiales concrete shell after the 2017 earthquake. Image Courtesy of J.I. del Cueto Ruiz Funes.

583 Preservation and conservation of Felix Candela’s historic concrete shell: Los Manantiales restaurant The survey conducted in April 2017 also confirmed that the damages of the structure had not only been caused by the effects of the 2017 earthquake but also due to the progressive and differential subsidence of the site’s soil.

As illustrated in Fig. 10 differential subsidence have affected the footings of the shell and at least one cable-tie connecting the footings is believed to have been broken before the 2017 earthquake.

Figure 10. Damage to the groins and foundations of Los Manantiales concrete shell.

A team of expert-volunteers from the Faculty of Architecture and Institute of Engineering at Universidad Nacional Autónoma de México are currently working on a repair and conservation management plan. Unfortunately, the lack of funds has delayed the repair to the structure, thus leaving it vulnerable and at risk of loss.

Other shells around the world

Candela’s work influenced and inspired other architects further afield and many of his design and construction solutions also inspired further research and construction technologies. Los Manantiales hypar shell was used as inspiration to build almost- identical copies in different parts of the world including Ecuador, Azerbaijan and Germany. Candela’s posthumous work was an eight-sided groined vault almost identical to that built for Los Manantiales restaurant in Mexico City. This last commission that Candela undertook in 1994, he was 84 years

584 Marisela Mendoza and Juan Ignacio del Cueto Ruiz-Funes old, was to contribute to the iconic buildings of the Oceanographic Park at Valencia. Candela had been asked to design and built two buildings; the first, the underground aquarium, was to be inspired by the San Jose Obrero Church he built in Monterrey (1959) and the second, the aquarium’s restaurant, was to be inspired by Los Manantiales restaurant built in Mexico City (1958). Unfortunately, Candela passed away in 1997 and left the project unfinished. The structural analysis and construction were then carried out by the architects Alberto Domingo and Carlos Lázaro.

Conclusions

Los Manantiales hypar concrete shell bears witness to the fruitful collaboration that Candela established with the architects Enrique de la Mora and Fernando Lopez Carmona. The structural and constructional strategies that Candela applied to design and built Los Manantiales were informed by the knowledge and experience that he gained during the design and construction of other important commissions such as the Stock Exchange and San Antonio de las Huerts church. In 2017 the earthquake that shook Mexico City caused severe damages to many significant buildings including Los Manantiales restaurant in Xochimilco. However, the survey and analysis conducted by a team of experts at UNAM revealed that the structural damages presented on the concrete shell had not only been caused by the effect of the earthquake but by the progressive differential subsidence of the site as well as inadequate interventions and lack of systematic maintenance and repair. Finally, this paper has also demonstrated the importance of documenting the construction process of Los Manantiales to assist in developing an effective plan to repair and preserve it.

References

[1] Félix Candela, Unpublished Autobiography, Manuscripts Division, Department of Rare Books and Special Collections, Princeton University Library, ‘Félix and Dorothy Candela Manuscripts, 1960s–1993’, Félix Candela Papers (C1455), Box 25, Folder 11. [2] M.E Garlock and D. Billington, Félix Candela: Engineer, Builder, Structural Artist, New Haven: Yale University Press, 2008, p.76. [3] Historic Centre of Mexico City and Xochimilco. United Nations Educational, Scientific and Cultural Organisation Website, https://whc.unesco.org/en/list/412/ [4] M. Mendoza, Felix Candela’s first European project: The John Lewis Warehouse Stevenage New Town, Architectural Research Quarterly, Vol. 19, Issue 02, 2015, pp. 149-169. [5] J.I. Del Cueto & A. Hernandez, Setting the Edge Free: Candela’s shells in San Antonio de las Huertas Church. Geometry and Construction. In: Proceedings of the IASS Annual Symposia, IASS 2017: Interfaces - Architecture. Engineering. Science. HafenCity University Hamburg, Hamburg, Germany, 25-28 September 2017. Madrid: International Association for Shell and Spatial Structures. [6] C. Faber, Candela: The Shell Builder, London: The Architectural Press, 1963, p. 196. [7] H. Flores-Estrella., S. Yussim & C. Lomnitz, Seismic response of the Mexico City Basin: A review of twenty years of research, Natural Hazards, 2007; 40; pp. 357-372. [8] ibid. [9] T. Michiels., M. Garlock & S. Adriaenssens, Seismic assessment of Félix Candela’s concrete shells and their behavior during the 1985 Mexico City earthquake. A case study on the Church of our Lady of the Miraculous Medal. Structural Analysis of Historical Constructions: Anamnesis, diagnosis, therapy, controls. CRC Press, 2016, pp. 1544-1549. [10] F. Candela, ‘Structural Applications of Hyperbolic Paraboloidical Shells’, Journal of the American Concrete Institute, 26, no. 5, January, 1935, p. 414.

585 Preservation and conservation of Felix Candela’s historic concrete shell: Los Manantiales restaurant [11] M.E. Garlock and D. Billington, Félix Candela: Engineer, Builder, Structural Artist, New Haven: Yale University Press, 2008, p. 146. [12] A. Basterra & E. Valero, La aventura mexicana, Entrevista con Félix Candela, Arquitectura Viva 58, January – February,1998.

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