Experimental and Numerical Simulation of Limit States in Base Isolated Buildings Including Pounding

Base isolated buildings are typically important facilities expected to remain functional after a major earthquake. However, their behavior under extreme ground shaking is not well understood. A series of earthquake simulator experiments were performed to assess performance limit states of seismically isolated buildings under strong ground motions, including pounding against a moat wall. The test setup consists of a quarter scale three-story frame isolated at the base with Friction Pendulum Bearings (FPS) and a simulated moat wall. The building model is scaled from a professionally designed isolated three-story steel Intermediate Moment Resisting Frame (IMRF). An effort was made to properly scale the strength and stiffness of the frame relative to the bearings properties so that realistic yielding mechanisms can be obtained. The moat wall was modeled as either a rigid triangle steel stopper or a concrete wall of various thicknesses with soil backfill. The moat wall gap was set to various displacement increments to examine the sensitivity of this parameter and also to assess the effects of impact on the superstructure at different velocities. The test results indicate that pounding can induce yielding in the superstructure and is largely dependent on the gap distance and wall flexibility. Numerical model is proposed that can capture the nonlinear structural response and pounding interface behavior. The pounding interface is modeled by two spring elements in series that separately account for the material response at the contact interface and the flexibility of the moat wall.