Keywords: XY-friction pendulum (XY-FP) bearings. Seismic isolation. Truss-bridge models. Numerical analyses. Harmonic simulations. Earthquake simulations. Flat sliding (FS) bearings. Seismic performance. Dampers. Near-field ground motion.
Abstract: The XY-FP Friction Pendulum (XY-FP) bearing is a modified Friction Pendulum (FP) bearing that consists of two perpendicular steel rails with opposing concave surfaces and a connector. The connector intends to resist tensile forces and to provide both independent sliding in the isolator’s principal directions and free-rotation capacity. Numerical and experimental studies on an XY-FP isolated truss-bridge model were conducted to study both the response under three-directional excitations and applications to bridges. An XY-FP isolated truss-bridge model was tested on a pair of earthquake simulators using harmonic and near-field earthquake histories. The experimental results demonstrated the effectiveness of the XY-FP bearings as an uplift-prevention isolation system. The construction detail of the small-scale connector of the XY-FP bearings and misalignment of the isolators on the test fixture did not permit fully uncoupled orthogonal responses. Numerical analyses on an XY-FP isolated bridge with different isolation periods in the principal directions subjected to near-field ground motions demonstrated the effectiveness of the XY-FP bearings to limit displacements in either the longitudinal or the transverse direction. Numerical analyses that investigated the sensitivity of the XY-FP isolation system response to differences in the bearings’ coefficients of friction demonstrated that bounding analysis using uniform upper and lower estimates of the coefficient of friction will generally provide conservative estimates of displacements and shear forces for isolation systems with non-uniform isolator properties.