Quantifying Friction Effects on Floor Rotations During Moat Wall Pounding of Base-Isolated Structures

Abstract

Seismic isolation effectively protects structures by decoupling them from ground motion. However, large isolation displacements may induce pounding against adjacent retaining walls, amplifying displacement and shear demands on the superstructure. Although moat-wall pounding has been extensively addressed numerically and experimentally, the tangential frictional component at the impact interface has received comparatively less attention, particularly regarding its isolated contribution to floor rotations and perimeter engineering demand parameters in base-isolated buildings. This study numerically evaluates the effect of friction during moat-wall pounding on the response of a symmetric base-isolated prototype building with a 2:1 plan aspect ratio, uniformly distributed identical lead rubber bearings, and no intentional mass or stiffness eccentricity to isolate the rotational effects induced by frictional impact from other sources of torsional response. For the considered prototype, results indicate that including friction has a negligible effect on normal impact forces but significantly increases floor rotations and perimeter demands relative to the center of mass. Frictional impact increases perimeter interstory drifts to approximately twice the value observed at the center of mass, while perimeter accelerations increase by approximately 15% relative to the center. Results show that the frictional component of moat-wall pounding alone can induce non-negligible rotational response, highlighting the importance of including friction in simulations of potential impact in seismically isolated buildings.