UCLA

Seismic isolation systems are becoming more common in the construction of a variety of critical buildings/facilities, such as hospitals and data centers, that require more stringent seismic performance levels. The Triple Friction Pendulum (TFP) isolation bearing systems offer arguably the highest performance among seismic hazard mitigation devices/solutions. TFP bearings, which exhibit highly nonlinear and history-dependent responses, dissipate the seismic energy through friction. While there are numerous models available to simulate the cyclic responses of TFP bearings, most either lack several key features, such as coupled biaxial or triaxial reactions or account for these effects in a phenomenological manner. The present study tackles these issues by implementing a physics-based, extendable, and numerically robust model, which is packaged into a novel macroelement that can be used in nonlinear time-history analyses that are required for performance-based seismic assessment and design.

The aforementioned macroelement model is based on a mechanically consistent multi-surface plasticity approach that can simulate the triaxial hysteretic responses of TFP bearings. The macroelement model is developed and implemented in ABAQUS as a User-defined ELement (UEL). It is validated using experimental data from component-scale laboratory and full-scale shake table tests carried out at the E-Defense facility.

The experimentally validated biaxial and triaxial TFP models are then used in performance-based seismic assessment of a prototypical base-isolated braced frame building to examine the effects of modeling errors on the estimated seismic losses. While the scope of this case study was limited to one building, findings indicated that differences between the basic (i.e., uncoupled biaxial) and the more advanced (i.e., coupled biaxial and triaxial) approaches are non-negligible, warranting their use in practice as well as future studies.