Centrifuge modeling of energy dissipation characteristics of mid-rise buildings with raft foundations on dense cohesionless soil

The nonlinear behaviour of shallow foundations on competent soil during large earthquakes provides a mechanism for energy dissipation and improved performance of buildings. To investigate this, centrifuge experiments were undertaken at the University of Dundee, Scotland, using a range of equivalent single degree of freedom (SDOF) building models resting on a layer of dense, dry sand. The models were comprised of shallow raft foundations of identical size, and superstructures sized to give equivalent 3, 5, and 7 storey buildings. Ricker wavelets were applied as a ground motion to capture the free-vibration responses of the soil-structure systems. Representative recordings from the Christchurch Earthquake of February 22, 2011 were also applied to the models in separate tests. It was found that significant energy was dissipated between the soil, foundation and structure, particularly when the models were subjected to high amplitude input motions. The dominant energy dissipation mechanism appeared to be uplift of the foundation from the supporting soil. The large raft in conjunction with dense sand meant significant energy could be dissipated through nonlinear soil-foundation-structure interaction (SFSI) without the detrimental effects of significant permanent soil deformation. Ricker wavelets were found to be suitable in determining the SFSI parameters appropriate for use in earthquake analysis.