Effect of displacement restraint on the collapse performance of seismically isolated buildings

This study investigates the effect of displacement restraint on the collapse performance of seismically isolated buildings. The displacement restraints considered are stiffening triple Friction Pendulum (FP) bearings and moat walls. The study is based on 6-story perimeter frame seismically isolated buildings designed with special concentrically braced frames (SCBF) and special moment resisting frames (SMF) for a location in California using the minimum criteria of ASCE/SEI 7-10 and ASCE/SEI 7-16 and also using enhanced designs. Results from pushover analysis and nonlinear response history analysis demonstrate that proper designs require a balance between the value of R_I for the design of the superstructure and the displacement capacity of the isolators. The paper shows that isolation systems with sufficient displacement capacity before engaging the displacement restraint and a R_I factor consistent to that displacement capacity may have an acceptable collapse risk. Values of the design parameters for the superstructure and the displacement capacity and behavior of the isolation system for achieving acceptable collapse risk are presented.