Soil behaviour beneath buildings with structural and foundation rocking

Abstract

Structural or foundation rocking are effective ways to prevent the development of large force demands in building systems experiencing ground shaking. In practice, structural rocking may result in large displacements and therefore is often accompanied with dampers, while residual and differential settlements are sometimes a barrier for utilisation of foundation rocking. This paper presents a novel approach to test simultaneously in a centrifuge the performances of a building model rocking above its foundation level (structural rocking) and of a dynamically equivalent building rocking below its foundation level (foundation rocking). These tests are used to explore the role of the foundation and soil response when considering the relative trade-offs between the two building types. In the experiments, dry sand was used in both dense and loose states and a series of earthquake excitations were applied. Results demonstrate that the rocking motion of the buildings is evident in the soil response beneath the structures, and foundation rocking causes larger dynamic differential settlements than structural rocking for a given rocking amplitude. However, these differential settlements may still be small enough to be tolerated from a serviceability limit state point of view.