Seismic assessment of Felix 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

Felix Candela designed and built a series of emblematic concrete shell structures in and around Mexico City during the 1950s and 1960s. Candela's structures, characterized by their hyperbolic paraboloid geometric forms (also referred to as hypars), survived several major earthquakes without significant damage. Although Candela's shells have been extensively discussed in literature for their elegance and efficiency, in-depth analyses of their dynamic performance is lacking. Concrete shell structures are generally believed to inherently perform well during earthquakes. They are characterized by a high mechanical efficiency and thus can be made very thin. Because of their lightweight nature, the induced earthquake forces are relatively low. However, shell structures are typically designed to perform optimally under gravity loads, carrying the loads to the foundations mainly through membrane action. The horizontal forces induced by earthquakes could thus create unanticipated bending stresses in the structure, which could lead to damage. Thus, while several factors indicate that Candela's shells might be intrinsically at a low risk for earthquake damage, the reasons for their good behavior are not yet understood. An in-depth examination of their performance under earthquake loading would enable professionals to develop a more effective conservation approach, if necessary to protect them against future earthquakes. Perhaps more significantly, a better understanding of why Candela's concrete shells performed well during the 1985 earthquake could also inform the development of further earthquake-resistant shell structures. This research presents a map which details the earthquake hazard of Candela's structures in Mexico City based on their subsoil conditions as well as introduces an in-depth case study of the performance during the 1985 Mexico City earthquake of the 1953 Church of our Lady of the Miraculous Medal, one of Candela's most emblematic structures.