Fragility-Based Assessment of the Behaviour Factor for Eurocode 8-Designed Suspended Piping Restraint Systems

The piping systems are critical non-structural elements (NSEs) whose seismic performance directly affects the post-earthquake functionality of essential facilities. However, current seismic design provisions for such systems remain largely empirical, and behavioural factors are rarely calibrated using performance-based methods. This study implements an FEMA P695-inspired framework to calibrate the behaviour factor (qa) for the installation of sway-braced suspended piping restraint systems in following the force-based requirements specified in Eurocode 8. The representative piping archetypes were developed and analysed using non-linear time history analyses under multiple seismic intensity levels derived from the floor response spectra (FRS) of prototype-reinforced concrete buildings. Fragility curves for two limit states were derived with displacement ductility adopted as the engineering demand parameter (EDP) and peak floor acceleration (PFA) used as the intensity measure (IM). The results show that increasing (qa) systematically shifts the fragility curves towards lower median PFA values, indicating higher seismic vulnerability at larger behaviour factor values. The effect of piping layout configuration was of secondary importance compared to the applied reduction factor. The implemented approach provides a rational basis for selecting behavior factors consistent with explicit performance objectives and supports further development of performance-oriented seismic design procedures for non-structural systems. The results show that increasing the behaviour factor (qa) leads to a systematic shift in the fragility curves towards lower median PFA values and a noticeable increase in the dispersion of the response. A quantitative analysis shows that increasing the behaviour factor (qa) from 1 to 4 results in a reduction of up to approximately 60% in median PFA, highlighting a significant increase in seismic vulnerability at higher behaviour factor values.