Centrifuge Modeling of Rocking Foundations on Sand

Shallow foundations supporting slender structures are often subjected to extreme lateral loading such as multi-cycle wind and wave loads in offshore environments or strong seismic shaking. A number of nonlinear phenomena can occur in such conditions such as sliding on and uplifting from the supporting soil or even soil failure in the form of development of ultimate bearing capacity mechanisms. Residual settlement and rotation of the supported structural system are then unavoidable. While the principle of Performance Based Design that allows the nonlinear behavior of structural components has been applied in the superstructure design for a number of years, it was recently made clear that the application of the same concept to foundation design is perhaps the only viable alternative for the retrofit of buildings and structures. Inelastic foundation performance can provide potential benefits to the overall integrity of the structure since energy dissipation at the foundation level reaches high levels. The response of a single degree of freedom system founded on a square surface foundation on sand was explored through a series of centrifuge tests that were performed at the Center for Earthquake Engineering Simulation at Rensselaer Polytechnic Institute. The system was subjected to lateral monotonic loading till overturn and lateral slow cyclic loading. Different soil conditions were tested to capture the rocking response and a tactile pressure sensor was placed at the soil-foundation interface to capture the evolution of the foundation contact area and the vertical stress distribution during cyclic loading.