Performance-based determination of optimal slip force of Pall friction dampers for multiple seismic hazard levels using endurance time method

The incorporation of friction damper devices mitigates damage to primary structural members by dissipating seismic energy through controlled frictional mechanisms. Among the earliest and most extensively implemented friction-based devices are Pall friction dampers (PFDs). The endurance time method (ETM) reduces the computational effort required for obtaining structural responses and enables their estimation across multiple seismic hazard levels through a single analysis. The optimal slip force of PFDs is a key design parameter of these dampers. However, the optimal slip force determined for a specific seismic hazard level does not necessarily ensure satisfactory performance of structures equipped with these dampers across multiple seismic hazard levels. Hence, in this study, using ETM, a practical procedure is suggested for obtaining the optimal slip force of PFDs at multiple hazard levels. To this end, cases including 3-, 6-, 9-, and 12-story moment-resisting frames are considered. Then, the performance of structures with optimal PFDs and without PFDs is compared at different hazard levels. A comparison between the results of the ETM and conventional nonlinear time-history analysis using far-field ground motion records of FEMA P695 revealed a discrepancy of approximately 10%, indicating that the ETM predicts structural responses with acceptable accuracy. The investigation of PFDs' hysteretic behavior showed a more significant contribution by dampers located on the lower stories.