Unbiased Simplified Seismic Fragility Estimation of Non-Ductile Infilled RC Structures

Infilled reinforced concrete (RC) buildings represent a prevalent taxonomy class in the Mediterranean region. Many were constructed before proper seismic provisions and detailing were enforced meaning they typically possess non-ductile failure mechanisms. Therefore, their simple but adequate seismic fragility estimation remains a challenge for the research community and practitioners. Moreover, their performance quantification can typically require characterisation via detailed numerical models that capture salient behaviour features, which involves extensive non-linear dynamic analyses with large computational burden. In this regard, an unbiased seismic fragility estimation methodology for the simplified assessment of infilled RC frame structures is described for both collapsing and non-collapsing scenarios. Its development is using extensive cloud analyses carried out with a large set of oscillators representative of the infilled RC frame's structural behaviour to permit the well-established pushover-based methods to be adopted in practice. The result is a novel set of empirical relationships relating the seismic behaviour of these typologies to their pushover curve parameters to allow practitioners to perform an accurate risk assessment and verification in an expedited manner. The choice of average spectral acceleration as the intensity measure used to characterise the fragility parameters for these relationships is shown to present notable advantages in reducing bias compared with other existing approaches. The results are validated via comparison with a detailed hazard-consistent assessment of case studies from a database of three-dimensional archetype building models. These were also developed here to capture the temporal evolution of building codes and architectural features of the building class in Italy.