Scale and Heating Effects on Mechanical Behavior of Friction Pendulum Bearings under Short-duration Loading

Scaling seismic isolators for laboratory testing remains practical necessity due to the high costs and limited availability of full-scale dynamic testing facilities. Although current design guidelines permit scaled-down dynamic testing under specific conditions, a robust framework is still required to ensure accurate interpretation of the resulting data. This research introduces a scaling methodology based on two intuitive dependency assumptions: (I) maintaining similar vertical compressive stress applied and (II) maintaining both similar vertical compressive stress and average horizontal rate applied. This methodology facilitates accurate interpretation of mechanical behavior and proper design of dynamic loading protocols for friction pendulum bearings (FPBs) at different scales. A scaled-down FPB specimen and its full-scale counterpart—manufactured using identical materials and processes—were tested with varying horizontal displacement amplitudes in a bi-axial dynamic testing facility. Both FPB specimens experimentally exhibit stable and anticipated hysteretic behavior. Overall, the test results indicate that applying dependency assumption (II) provides a reliable foundation for developing short-duration loading protocols and interpreting mechanical behavior of reduced-scale FPBs. To further validate these experimental outcomes, a simplified analytical model incorporating bilinear hysteretic behavior and a friction model is employed. The strong agreement observed between the derived and experimentally determined scale factors further confirms the validity of dependency assumption (II). Additionally, this agreement highlights the necessity of considering heating effects and loading rates to ensure reliable interpretation of reducedscale FPB test data.