Within the Performance Based Approach for assessing the seismic vulnerability of the Egyptian Obelisk in Piazza S. Giovanni in Laterano of Rome, Italy, the DDP- isplacement Data Processing of pull release and shaking table tests of a 1: 6 reduced scale mock-up of the obelisk has been performed, identifying three well defined RTP phases of its free oscillations governed by the Coriolis forces: Rocking, Transition and Precession. The phase R is a stable yet decaying rocking around the rotation axis (the base edges), in which the rotation is prevalent with respect to nutation and precession around the other axes. The phase T is an unstable transition, activated at a critic angular velocity, in which precession and nutation become more significant and comparable with the rocking rotation. The phase P is a table yet decaying precession, where the dynamic of the block is characterized by the prevalent recession around the vertical axis. During the phase R, the obelisk half rotates around the rocking axis, with constant decay of the maximum rotation angle after each impact. It is also notable, during phase R, the persistence level of the acceleration peak at each impact.
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