Centrifuge investigation comparing the rocking response of two soil-structure systems

Seismic protection of structures by means of rocking isolation is becoming increasingly popular, because allowing uplift is an inexpensive way to reduce structural demand. However, understanding the role of soil–structure interaction in the response of rocking systems is important to define what type of rocking system might be most effective. To address this challenge, a campaign based on centrifuge modelling and testing is currently ongoing. The primary objective is to assess the force demand that rocking systems experience during their motion. Flexible structures that rock while stepping on discrete footings (structural rocking) and flexible structures with discrete footings rocking on soil (foundation rocking) are both considered. Following this distinction, two building models were designed with the only difference being the connectivity of the columns to the footings. For structural rocking, columns were designed to detach and step on their footings, while for foundation rocking the footing-column connection was designed to be rigid. The two building models were tested side-by-side in a centrifuge. A second test was also conducted, where thin steel “fuses” were installed in the interface of structural rocking, to further study the allocation of energy dissipation between structural elements and fuses, and soil medium. The building models were placed on the surface of dense sand and then tested using sinusoidal ground motions which caused a combination of sliding and rocking. The global response of the models in terms of overturning moment and storey shear was investigated and back validated by obtaining directly the internal loads, which were found capped regardless of the extent of rotation. More-over, the base isolation effect was evident during large amplitude resonant excitations, whereas during a low frequency low amplitude excitation there was no clear benefit of rocking. Finally, no significant effect was observed in limiting the base shear demand by using the steel fuses