Seismic energy (mechanical energy) is dissipated around and within the SSI system, mostly in the form of heat, during irreversible dissipative processes. Energy dissipation in soil structure interaction (SSI) system is related to inelastic behavior of materials (soil, rock, structural components, energy dissipation devices), viscous coupling between solid and fluid phases, frictional dissipation in contact zones, and seismic energy radiation. Based on principles of thermodynamics, an energy dissipation analysis framework for elastic-plastic materials is proposed. A common misconception of plastic dissipation and plastic work is addressed and corrected using proper formulation of thermomechanics. The nature and computation approach of plastic free energy in solid and structural element is discussed. The proposed methodology is illustrated through several finite element (FE) simulations. It is shown that the consideration of plastic free energy is necessary to correctly evaluate energy dissipation in elastic-plastic solid and structural elements. Results of energy analysis indicates that the different between plastic work and plastic dissipation could be significant, and the ratio between them evolves with time thus should not be assumed constant.
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