To illustrate this methodology, a variety of shapes are generated based on a set of parameters including boundary conditions and net stiffness. Through the application of an inversed hanging chain model subjected to lateral loading in a dynamic relaxation solver, shell forms are generated for which it can be ensured that such a load path exists. Therefore, for masonry shells subjected to both vertical gravity and horizontal seismic loading, a compression-only load path (in 2D often referred to as a thrust line) should be present within the thickness of the shell to avoid collapse mechanisms. The form finding approach examined here is based on the generally accepted assumption that masonry structures cannot resist tensile stresses. Currently available form finding techniques for shells, however, rely solely on gravity loads for the generation of their shape and do not account for seismic loading. Additionally, there is a renewed interest in constructing masonry shells because of their low carbon impact, spurring the need to understand how such shells should be designed in seismic areas. Earlier studies have shown that continuous shells behave well during earthquakes due to their high stiffness and low mass. ![]() Through a parametric study, this method is illustrated for a wide variety of boundary conditions and leads to a set of shapes for double layer thin shells. In this paper, a form finding approach is presented that allows for the shape generation of masonry shells in seismic areas. 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. Perhaps more significantly, a better under-standing of why Candela’s concrete shells performed well during the 1985 earthquake could also inform the development of further earthquake-resistant shell structures. An in-depth examination of their perfor-mance under earthquake loading would enable professionals to develop a more effective conservation ap-proach, if necessary to protect them against future earthquakes. 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. The horizontal forces induced by earthquakes could thus create unanticipated bending stresses in the structure, which could lead to damage. However, shell structures are typically designed to perform optimally under gravity loads, carrying the loads to the foundations mainly through membrane action. Because of their lightweight nature, the induced earthquake forces are relatively low. They are characterized by a high mechanical efficiency and thus can be made very thin. Concrete shell structures are generally believed to inherently perform well during earthquakes. Although Candela’s shells have been extensively discussed in literature for their elegance and efficiency, in-depth anal-yses of their dynamic performance is lacking. Candela’s structures, characterized by their hyperbolic paraboloid geometric forms (also referred to as hypars), survived several major earthquakes without significant damage. ![]() Félix Candela designed and built a series of emblematic concrete shell structures in and around Mexico City during the 1950s and 1960s.
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