Seismic fragility of nonstructural elements modelled as nonlinear single-degree-of-freedom systems

The seismic behaviour of nonstructural elements (NEs) is typically extremely critical in terms of seismic risk. As a matter of fact, these elements are often highly vulnerable to dynamic actions and they are associated with high importance/costs, especially for critical and strategic facilities. NEs that are sensitive to the accelerations are often modelled as elastic single-degree-of-freedom (SDOF) systems, for both seismic design and assessment purposes. However, in many cases, these elements can exhibit a nonlinear response even under relatively frequent earthquake events. Previous studies often assessed the seismic capacity of NEs considering specific case studies and configurations, but these findings cannot be generally extended to other case studies or applications. The present study aims at addressing the two abovementioned issues not adequately investigated in the literature: (a) nonlinear behaviour of NEs and (b) generalizability of the seismic capacity estimations. In particular, incremental dynamic analyses are carried out considering (a) a wide range of seismic floor motions recorded in instrumented buildings, (b) a lumped plasticity nonlinear model of NEs, and (c) a wide range of NEs, with frequencies within the typical range of real NEs. Seismic fragility curves are estimated according to a multiple damage state approach, also referring to the regulation performance levels and limit states. The study provides both methodological and quantitative contributions to the literature and practice. In particular, (a) the methodological framework can be referred to for extending the assessment of other case studies and (b) the fragility curves can be used for expeditious assessment of the seismic capacities of NEs that can be modelled by nonlinear SDOF systems.