Fragility analysis of a triangular free‐form reinforced concrete shell

Abstract

AbstractConsidering the importance of deepening the knowledge of the structural behavior of free‐form shell structures with a triangular plan, this work presents the results of research on the analysis of seismic vulnerability, verified through linear time‐history analysis (NLTHA), generating fragility curves through PSDM models. The analyzes carried out are based on uncertainties regarding both the mechanical properties of the materials and the geometric characteristics of the structures, as well as the action of seismic events. Real accelerograms, compatible with the elastic response spectra for Lisbon and Ouren, Portugal given by the EC8 standard, are used to consider seismic events. In the analyses, fundamental factors are considered, such as the accumulation of damage and the degradation in the resistance of materials. The structure presents highly ductile behavior in the face of seismic loads, attributed to its rigidity, geometry, lightness, and modal behavior, with participation in the horizontal components of the mass in the first five vibration modes greater than 80% and with minimal influence of the vertical component, characteristics inherent to this type of structure. However, it should be noted that the area close to the support, in the same direction as the ground acceleration, is the most vulnerable. This occurs due to the plastic yielding of the concrete during the earthquake, which promotes the appearance of cracks and compression damage. This is verified for the structure when subjected to earthquakes with PGA in the horizontal direction between 0.01 and 0.8 g. The probability of considerable damage increases with seismic events having PGA greater than 0.6 g, which, in turn, can compromise the stability of the structure. It is, therefore, of great importance to study the seismic behavior of shell structures, especially free‐form shells, considering the variability and uncertainties related to the structural stress arising from the seismic demand.