Within the Performance Based Approach for assessing the seismic vulnerability of the  Egyptian Obelisk in Piazza S. Giovanni in Laterano of Roma, Italy, the DDA - Displacement Data Analysis of pull release and shaking table tests of a 1:5 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 (Rocking) is a stable yet decaying rocking motion, in which the rotation around Y axis (Rot_y),  is prevalent with respect to the rotation around X axis (Rot_x).  The phase T (Transition) is a chaotic transition phase from Rocking to Precession, activated at a critic angular velocity, in which Rot_y become comparable with Rot_x. The phase P (Precession)  is a stable yet decaying Precession, where the dynamic of the obelisk is characterized by the prevalent precession around Z axis (Rot_z).  During the phase R, the obelisk half rotates around Y axis, with constant decay of the  maximum peak values of the rotation angle after each impact.  It is also notable, during phase R,  the persistence level of the  acceleration peak at each impact.

Keywords: Obelisk, Coriolis, Gyroscope, RTP - Rocking To Precession