Impact model for simulation of base isolated buildings impacting flexible moat walls

Base isolated buildings subjected to extreme earthquakes can exceed their design displacements and impact against the surrounding moat wall. To better understand the consequences of impact on the superstructure, an impact element considering moat wall flexibility is proposed based on impact theory and observations during experimental simulations. It is demonstrated that numerical simulations using the proposed impact element can capture the dominant characteristics of the contact force observed in experiments of base isolated buildings impacting various moat wall configurations including concrete walls with soil backfill and rigid steel walls. The contact force is dependent on impact velocity, geometry, and material properties at the contact surface, and the global dynamic characteristic of the moat wall. Properties of the moat wall impact element are derived based on mechanics‐based models considering material properties and geometric measurements of the experimental setup. For this purpose, the moat wall is modeled as a flexural column with a concentrated nonlinear hinge at its base and soil backfill considered through a damped elastic foundation then generalized into a single degree of freedom system. The resulting impact element is shown to accurately capture both local deformation and the vibration aspects of impact observed in experiments and the effects of impact on superstructure response. Copyright © 2012 John Wiley & Sons, Ltd.