During seismic events, structures often undergo nonlinear deformations, resulting in hysteresis cycles that minimize force transfer to the superstructure while dissipating significant seismic energy. This nonlinear behavior is characterized by sudden changes in system stiffness, leading to energy redistribution across system modes. Such energy transfers can excite higher modes, potentially impacting responses like attached component behaviors during earthquakes. The energy transfer process is largely influenced by interactions between the initial and degraded modes of a nonlinear hysteretic system. While linear structural dynamics assumes mode orthogonality for simplicity, sudden nonlinearities especially during large deformations or damage disrupt this orthogonality, leading to non-zero modal interaction. This study investigates modal interaction during sudden nonlinearities at the structural base and its role in explaining energy transfer between different vibrational modes, often triggering higher mode excitation. The research also highlights the limitations of first-order perturbation theory in predicting modal interaction for severely damaged structures, emphasizing the need for a more accurate approach across varying degrees of freedom and damage levels.