Experimental investigation of the seismic response of a column rocking and rolling on a concave base

Abstract

Rocking modifies the seismic response of structures, because uplifting works as a mechanical fuse and limits the forces transmitted to the structure. However, the engineering community is in general reluctant to let a structure uplift because it can overturn, and, more important, an unanchored structure has no redundancy against this failure mode. Using a safety factor for the design of a flat rocking foundation (i.e. designing it larger than minimum required to prevent overturning) goes against the essence of the rocking seismic isolation method, as the structure would end up behaving as fixed to the ground. To protect against overturning but preserve the ability to uplift we propose to extend the flat rocking foundation using curved wedges at its ends. This paper presents the results of dynamic tests of small bodies rocking on curved foundations. The results compare relatively well with the analytical solutions, but they are shown to be very sensitive to the coefficient of restitution.